Foliar application of allantoin and serotonin mitigates salinity stress in bitter melon (Momordica charantia L.)

Masoomeh Amerian; Gholamreza Gohari; Saeid Jalalihonarmand; Sima Panahirad; Georgia Ntatsi

doi:10.1038/s41598-026-52357-2

. 2026 May 9;16:24983. doi: 10.1038/s41598-026-52357-2

Foliar application of allantoin and serotonin mitigates salinity stress in bitter melon (Momordica charantia L.)

Masoomeh Amerian ^1,^✉, Gholamreza Gohari ², Saeid Jalalihonarmand ³, Sima Panahirad ⁴, Georgia Ntatsi ⁵

PMCID: PMC13463000 PMID: 42106488

Abstract

Bitter melon (Momordica charantia L.) is a climbing species frequently employed in traditional medicine to treat a wide number of diseases. Soil salinity represents a primary abiotic constraint on plant growth, impacting nearly 50% of irrigated farmland and constantly increasing. Previous studies revealed the individual benefits of allantoin and serotonin, in mitigating abiotic stresses. Therefore, in the current study, we investigated their ability, both individually and combination, ameliorating the damaging consequences of salt stress on the development and physiological and biochemical attributes of bitter melon. A factorial experiment arranged within a completely randomized design, replicated three times, was performed. Two variables were examined: (a) three salinity levels (0, 50 and 100 mM NaCl) and (b) foliar application treatments (control (distilled water), allantoin (1000 µmol), serotonin (100 µmol) and allantoin (1000 µmol) +serotonin (100 µmol)). At the end of the experiment, critical parameters related to morphology, biochemistry, and physiology were measured from leaf and root tissues, and fruit secondary metabolites was extracted. Vegetative traits (plant height, number of leaves, leaf area), and fruit-related parameters (fruit mean weight and yield) of bitter melon were suppressed under increasing salinity stress. Exposure to 100 mM NaCl reduced photosynthetic efficiency (SPAD (soil-plant analysis development), Fv/Fm), relative content of water and potassium and phosphorus concentration in bitter melon leaf, while increasing electrolyte leakage, proline, sodium, chloride, hydrogen peroxide, malondialdehyde and antioxidant enzyme activities. However, the combined application of allantoin and serotonin alleviated these effects by increasing antioxidant enzyme activity, proline accumulation, total soluble sugar, total protein, ascorbic acid, relative content of water, potassium and phosphorus, while decreasing malondialdehyde and hydrogen peroxide and sodium and chloride accumulation. In fruit, the content of p-coumaric acid (14.64%), ferulic acid (10.48%), caffeic acid (15.74%), gallic acid (22.04%), and cinnamic acid (37.77%) increased in plants treated with allantoin + serotonin compared to the control. The highest amount of phenolic acids was produced by plants treated with allantoin and serotonin. The application of allantoin and serotonin had a positive effect on the quality characteristics and yield of bitter melon fruit compared to the control. In summary, the findings suggest that treating bitter melon with of allantoin and serotonin, particularly in combination, effectively alleviated the adverse impacts of salinity by inducing critical modifications in bitter melon’s physiological and biochemical processes. Further investigation might be useful for translating these results to other salt-stressed crops.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-026-52357-2.

Keywords: Antioxidant enzymes, Plant hormone, Salt stress, Secondary metabolites

Subject terms: Biochemistry, Physiology, Plant sciences

Introduction

Salinity, an important environmental stress, significantly affects many plant physiological functions resulting in impaired development, and subsequently yield and quality losses¹. The plant’s response to salinity is species, developmental stage, and stress severity and duration depended². At cellular level salinity decreases membrane stability, inhibits the activity of photosynthetic enzymes and impairs the overall photosynthetic mechanism³. These disruptions coupled with reduced biomass accumulation and compromised leaf expansion alongside the impaired water and nutrient uptake contribute to reduced vegetative growth and yield with subsequent economic losses⁴. Furthermore, the negative effect of salinity could be linked to a decreased osmotic potential in the root environment and higher ionic toxicity resulting from the excessive accumulation of sodium (Na⁺) and chloride (Cl⁻) ions in the leaves and nutritional imbalance that impair the absorption and/or translocation of vital nutrients to the shoots⁵. In order to maintain the cellular turgor and prevent water efflux, plants accumulate compatible osmolytes like soluble sugar and protein and proline⁶. To counteract these effects several management practices have been employed⁷. Among them, exogenous plant hormone application is widely used to improve plant stress resilience. Exogenous jasmonic acid⁸ and melatonin (150 µM)⁹ increased salt stress tolerance of bitter melon through metabolism modifications, while melatonin, increased key fruit compounds (charantin, momordicin, cucurbitacin) and antioxidant capacity¹⁰. Chitosan–selenium nanoparticle (CTS-Se NPs at 20 mg L^− 1) significantly enhanced salinity tolerance of bitter melon, by increasing antioxidant enzyme activity, proline, relative content of water (RWC), and potassium (K), while decreasing malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and Na accumulation, resulting in improving yield and essential oil production¹¹. CTS-Se NPs also improved growth, photosynthesis, nutrient balance, and stress gene expression under salinity³. Recently, allantoin and serotonin have gained attention as compounds that contribute to enhanced stress resistance in various plants species^12,13.

Bitter melon (Momordica charantia L.), from the Cucurbitaceae family, is native in subtropical and tropical regions, with its main cultivation areas being East Africa, Asia and South America¹⁴. Phytochemical compounds found in different parts of bitter melon plant (i.e., fruit, seed, leaf and root) are used to treat diabetes, cancer, AIDS, high blood pressure, obesity and viral and bacterial infections. The insulin-like compounds found in bitter melon fruit and seeds are particularly significant for managing of type 2 diabetes. In terms of its nutritional value, bitter melon is a rich source of carbohydrates, proteins, minerals, vitamins (e.g. vitamin C) and dietary fiber¹⁵. The medicinal properties of bitter melon could be attributed to triterpenoids, saponins, phenols, flavonoids, tannins and other phenolic compounds¹⁶. Quarantin and momordicin are two triterpenoid compounds found in the plant with strong antidiabetic properties¹⁷. Xanthine oxidase, a key enzyme in the inducing gout and cancer, is significantly inhibited by cucurbitacin present in bitter melon¹⁰. All the above emphasize the importance of this plant in human diet and highlight the necessity for special attention on its production particularly, especially under stress conditions.

Allantoin (N-(2,5-Dioxo-4-imidazolidinyl) urea), a heterocyclic N-containing compound and intermediate product of purine catabolism, and its hydrolyzed form (allantoate) are collectively known as ureides¹⁸. Allantoin is a well-established commercial substance with numerous uses in the pharmaceutical and cosmetic sectors¹⁹. Known to be involved in nitrogen (N) metabolism in plants, mainly increases the activity of enzymes related to seed germination and photosynthetic intensity, improves germination speed and chlorophyll content and prevents aging²⁰. Allantoin improves crop yield²¹ and tolerance to drought stress²², salinity²³, high light intensity²⁴ and heavy metals²⁵. Currently, two primary functions for allantoin in plant abiotic stress responses have been propped including a possible role as a ROS protectant²⁶ and/or an abscisic acid (ABA) metabolism activator²⁷. External application of allantoin increases ABA levels in Arabidopsis by stimulating its biosynthesis and the hydrolysis of ABA-glucose conjugates²⁷. Despite these benefits, the mechanisms of exogenous allantoin in stress mitigation remain under investigation²⁸.

Serotonin (5-hydroxytryptamine) is an indoleamine with antioxidant effects²⁹ playing a major role in plant development, phytohormonal status, gene regulation, morphogenesis, flowering and stress adaptation under various environmental challenges³⁰. Primarily known as a neurotransmitter in the animal kingdom, serotonin has been detected in more than 90 plant species across 37 families. Its structural similarities to auxin, suggest a possibility to interact with the auxin receptors and transport mechanisms in plants³¹. As a pseudo-hormone, serotonin plays a role similar to that of cytokinin, influencing lateral root growth, cell division and differentiation, biomass production, seed germination, somatic embryogenesis, and aging. During the germination stage, serotonin increased coleoptile weight and hypocotyl length of soybean (Glycine max L.)³². In Arabidopsis, serotonin concentrations of 10 to 160 µmol increased lateral root formation, while the reverse was the case 160 µmol³³ emphasizing its dose-dependent behavior. Serotonin increased the growth of primary roots by 20% in sunflower (Helianthus annuus L.) under salt stress conditions³⁴. According to the results obtained in tomato (Solanum lycopersicum L.), serotonin (5 µM) reduced the effects of salinity stress (200 mM NaCl) and increased the antioxidant capacity³⁵. In Ethiopian mustard (Brassica carinata L.), foliar application of serotonin (200 mmol L^− 1) improved gas exchange, chlorophyll levels, photosystem II efficiency, antioxidant activities, proline content, nitrate reductase activity, water use efficiency, and growth metrics across a range of salinity levels (0, 50, 100 and 150 mM)³⁰.

Serotonin is a well-studied plant hormone that, in plants, it plays a pivotal role in plant growth and development, phytohormonal crosstalk, gene modulation, morphogenesis, flowering and stress responses and adaptability under various uncertain conditions. Serotonin shares structural similarities with auxin, which brings the possibility to surrogate the auxin receptors and transport in plants. Under conditions of salinity stress, serotonin antioxidant metabolism, chlorophyll biosynthesis, osmolyte production, and defense-related genes that ultimately result in better growth and productivity. Allantoin plays multifaceted roles in purine metabolism, nitrogen storage/utilization, and stress protection. With the goal of developing an eco-friendly strategy to enhance salinity tolerance bitter melon a study was designed to investigate the synergistic potential of foliar-applied allantoin (1000 µmol), serotonin (100 µmol) individually and in combination, to mitigate salt stress (0–100 mM NaCl) in this economically important crop by evaluating their effects on morpho-physiological traits (growth, yield, photosynthesis), biochemical responses (antioxidant activity, osmolyte accumulation, oxidative stress markers), and ion homeostasis. Taking all the above into consideration, along with the increasing need for food production, a research was designed to assess the impact of the foliar-applied serotonin and allantoin, both separately and in combination, on the salinity tolerance of bitter melon. In this study, the combined use of allantoin and serotonin in the bitter melon plant was performed for the first time.

Materials and methods

Plant material and treatments

An experiment was carried out in 2024 in the research greenhouse of Razi University in the city of Kermanshah at 47 º 4ˈ minutes east and 19º 34ˈ north, and altitude of 1,200 m above sea level. The experimental design was a complete randomized factorial with three replicates. Prior to sowing, bitter melon seeds, obtained from Fardin Kasht Company (Product ID: FK14456), were surface-sterilized by immersion in a 1% sodium hypochlorite solution for a duration of 5 min. Sowing took place in seedling trays containing perlite and cocopeat (1:1) and fertigated every other day by applying a half-strength Hoagland nutrient solution. After two weeks, seedlings were transplanted to 7-L pots containing equal proportions of agricultural soil, sand, and well-rotted manure. Prior to the experiment initiation, soil samples were and collected their physical and chemical characteristics were recorded (Table 1). One week after transplanting the salt stress treatments (0, 50 and 100 mM NaCl were applied via irrigation water and continued until harvest. Foliar spraying of allantoin and serotonin (allantoin (1000 µmol)²², serotonin (100 µmol)³³ and allantoin (1000 µmol) +serotonin (100 µmol)), as moderators, was carried out in two stages: one week after stress initiation and one week after the first foliar spray, both in the evening. Control plants were cultivated under non-saline conditions and foliar spayed with distilled water in the same manner (two stages).

Table 1.

Physico-chemical characteristics of soil used in pots.

Soil texture	pH	Organic matter (%)	Electrical conductivity (dS m^− 1)	N (%)	Na (meq.l^− 1)	Calcium (g Kg^− 1)		Chloride (meq.l^− 1)
Silty-Loamy	7.4	0.94	1.49	0.07	1.18	0.12		0.96

Open in a new tab

The growth stages of bitter melon plant included vegetative growth (Fig. 1S), fruit set (Fig. 2S), immature fruits (Fig. 3S), ripe fruits (Figs. 4S and 5S), and seed ripening (Fig. 6S).

Morphometric parameters, yield, firmness, TSS and stomatal resistance

Two weeks after the second foliar spraying, several morphological and physiological traits were measured. The morphological characteristics examined were plant height, number of lateral branches, leaf number and area, fresh weight of root, shoot and fruit, fruit number, plant yield (Kg), and total yield (Kg m^− 2). About 50 days after sowing, the first fruits were harvested, and subsequent harvests occurred weekly (5 times in total). At the end of the growing season, yield and yield components ((fruit number, fresh and dry weight across all 5 harvests) were examined. The number of seeds per fruit, seed dry weight, and weight of 1000 seeds were also examined.

Key fruit quality parameters were measured using specialized instruments: firmness with an XTPlus-TA tester, dimensions with a digital caliper (Model NO: 41050, Germany), and total soluble solids (TSS) with a hand-held refractometer. (Atago 0–32 ºBrix Refractometer - Japan). Prior to harvest, stomatal resistance was assessed on the abaxial side of leaves between the hours of 11 a.m. and 1 p.m. using a steady-state porometer (model EA 540 − 026 AP4).

Physiologic parameters

Photosynthetic pigments, SPAD, performance index (PI_ABS) and chlorophyll fluorescence parameter (Fv/Fm)

Following a 14-day period after the second foliar application, leaf photosynthetic pigments were analyzed using the protocol established by Lichtenthaler³⁶. A SPAD-502 m was used to record chlorophyll content (Minolta Camera Co. Ltd., Japan). Chlorophyll fluorescence parameters (Fv/Fm, PI_ABS) were quantified with a Dual-PAM-100 fluorometer following a 20-minute dark adaptation period for the leaf samples (Heinz Walz, Efeltrich, Germany)³⁷.

Relative water content (RWC) and electrolyte leakage (EL)

RWC was determined following the protocol of Schonfeld et al³⁸., while Electrolyte Leakage (EL) was assessed according to the method described by Ben Hamed et al³⁹..

Measurement of biochemical properties

Proline according to Irigoyen et al.⁴⁰, total soluble sugar according to Paquin and Lechasseur⁴¹, ascorbic acid in leaf and fruit according to Bor et al.⁴²,, total anthocyanin according to Masukasu et al.⁴³, total flavonoids according to Bor et al.⁴², and total alkaloid according to Shamsa, et al.⁴⁴. Total phenol content was measured using Folin-Ciocalteau reagent⁴⁵. The antioxidant capacity of leaf samples was evaluated using the 2-2-diphenyl-1-picrylhydrazyl (DPPH) measurement method⁴⁶. The phenolic acids profile (p-coumaric acid, ferulic acid, gallic acid and caffeic acid) in leaf and fruit⁴⁷, ABA in leaf⁴⁸, secondary metabolites and associated compounds (charantin, momordicin, momordicozide and momordin) in fruit⁴⁹ were determined by HPLC.

The leaf content of H₂O₂ was determined using the trichloroacetic acid (TCA) precipitation protocol described by Velikova and Loreto⁵⁰. To assess oxidative membrane damage, lipid peroxidation was measured by quantifying the amount of malondialdehyde (MDA), a breakdown product, following the methodology of Heath and Packer⁵¹.

To determine the activity of catalase (CAT), peroxidase (POX), superoxide dismutase (SOD), and ascorbate peroxidase (APX) enzymes, extracts were prepared from frozen tissue, and the corresponding reactions were monitored via spectrophotometry. To prepare the enzyme extract, 100 mg of fresh bitter melon leaves were weighed and mixed with 1 mL of extraction buffer containing 100 mM potassium phosphate (K₂HPO₄/KH₂PO₄) with pH 7.8, 0.1 mM EDTA and 1% PVP in a cold porcelain mortar and homogenized on ice. Then, the resulting extracts were centrifuged at 13,000 rpm and at a temperature of 4 °C for 30 min and the resulting supernatant was collected. The resulting supernatant was used as enzyme extract to measure the activity of antioxidant enzymes. Total soluble protein content was quantified utilizing the Bradford⁵² method, employing bovine serum albumin (BSA) for the standard curve. Catalase (CAT) activity was measured by the Bergmeyer method⁵³ based on the disappearance of H₂O₂ at a wavelength of 240 nm. The activity of ascorbate peroxidase (APX) enzyme were measured according to Nakano and Asada⁵⁴ and peroxidase (POX) enzyme activity according to Herzog and Fahimi⁵⁵. Superoxide dismutase (SOD) activity was measured by measuring its ability to prevent the photoreduction of nitroblutotetrazolium using the method of Dhindsa et al⁵⁶. The 200 µL assay mixture consisted of 25 mM K₂HPO₄/KH₂PO₄ buffer (pH 7.0), 0.1 mM EDTA, 10 mM H₂O₂, and 10 µL of plant extract.

Leaf mineral concentrations

For the analysis of leaf nutrient concentrations, samples were oven-dried at 75 °C for 72 h and subsequently ground. Following a wet digestion process with concentrated nitric acid (65%), K⁺ and Na⁺ levels were quantified using a flame photometer (Kruse, model G 405, Germany). Cl⁻ and P contents were determined colorimetrically according to Munns et al⁵⁷. and Adesanwo et al⁵⁸, respectively, while N content was assessed via the Kjeldahl method⁵⁹.

Statistical analysis

The experiment employed a two-factorial design combining three salinity levels with four biostimulant treatments, each replicated three times. Data were analyzed using factorial ANOVA. In cases where a main effect was significant but the interaction was not, means for salt stress levels and/or biostimulants were compared using Duncan’s multiple range test (P < 0.05). When the interaction was significant, the same test was applied to separate the means of all treatment combinations. All analyses were performed with SAS software, version 9.01 (SAS Institute Inc., Cary, NC, USA).

Results

Growth characteristics of bitter melon plant

The results revealed a significant effect of both treatments and their interaction on plant height, number of lateral branches, number of leaves and leaf area (Table S1). A significant reduction in bitter melon growth was observed under salt stress. However, the application of allantoin and serotonin effectively mitigated this reduction, significantly improving growth characteristics under salinity. (Table 2; Fig. 1). The most favorable results were achieved by the combined application of allantoin + serotonin under control conditions (0 mM NaCl). The highest plant height (186.66 cm), plant fresh weight (694.67 g), plant dry weight (209.00 g), number of lateral branches (22.00), number of leaves (74.00), leaf area (65.13 cm²) were observed in the later mentioned treatment (allantoin + serotonin under control condition) (Table 2). In all three salinity levels, foliar applications improved the growth characteristics of bitter melon (Table 2).

Table 2.

The effect of different levels of salt stress (0, 50 and 100 mM NaCl), foliar applications (allantoin, serotonin, allantoin+serotonin) and their interaction on growth characteristics of bitter melon.

Treatment	Plant height (cm)	Number of lateral branches (-)	Number of leaf (-)	Plant fresh weight (g)	Plant dry weight (g)	Leaf area (cm²)
S₁M₁	144.66 ± 1.50^cd	18.00 ± 0.00^c	63.00 ± 1.00^c	450.00 ± 3.33^d	119.66 ± 0.83^cd	52.60 ± 0.69^d
S₁M₂	152.66 ± 2.11^c	19.33 ± 0.19^b	67.00 ± 0.33^bc	489.67 ± 8.44^c	132.33 ± 1.34^c	56.26 ± 0.51^c
S₁M₃	171.00 ± 0.57^b	20.33 ± 0.19^b	70.00 ± 0.00^ab	605.67 ± 16.98^b	155.33 ± 4.55^b	60.66 ± 0.19^b
S₁M₄	186.66 ± 3.15^a	22.00 ± 0.33^a	74.00 ± 1.00^a	694.67 ± 12.89^a	209.00 ± 9.61^a	65.13 ± 1.00^a
S₂M₁	100.33 ± 2.16^f	13.66 ± 0.19^ef	37.33 ± 0.83^f	333.33 ± 9.62^f	92.33 ± 2.26^ef	43.26 ± 0.38^g
S₂M₂	109.33 ± 0.38^f	14.33 ± 0.19^e	48.00 ± 2.02^e	359.00 ± 3.38^f	102.00 ± 0.33^de	44.87 ± 0.16^fg
S₂M₃	125.66 ± 4.03^e	15.66 ± 0.19^d	55.00 ± 0.00^d	402.00 ± 4.70^e	109.00 ± 1.20^de	47.22 ± 0.15^ef
S₂M₄	137.00 ± 0.33^d	17.00 ± 0.33^c	58.33 ± 0.50^d	427.67 ± 1.67^de	116.33 ± 0.38^cd	49.51 ± 0.55^e
S₃M₁	65.33 ± 0.19ⁱ	9.33 ± 0.19^h	16.00 ± 0.33ⁱ	206.67 ± 2.83^h	65.66 ± 1.17^h	28.73 ± 0.84^k
S₃M₂	75.00 ± 2.02^h	10.00 ± 0.00^vh	22.00 ± 1.2^h	256.67 ± 1.92^g	73.33 ± 1.17^gh	31.74 ± 0.21^j
S₃M₃	81.33 ± 0.38^gh	11.33 ± 0.19^g	29.33 ± 0.38^g	273.67 ± 4.29^g	80.00 ± 0.66^fgh	36.10 ± 0.11ⁱ
S₃M₄	86.33 ± 0.96^g	12.66 ± 0.19^f	34.00 ± 0.33^f	293.33 ± 1.92^g	83.66 ± 0.38^fg	40.12 ± 0.41^h

Open in a new tab

Statistical separation of means (n = 3) was performed using Duncan’s multiple range test at a 5% significance level; means followed by the same letter do not differ significantly. S₁, S₂ and S₃ are 0, 50 and 100 mM NaCl; M₁, M₂, M₃ and M₄ are control, allantoin (1000 μM), serotonin (100 µM) and allantoin+serotonin.

Fig. 1 — The effect of allantoin, serotonin and their combination on the leaf growth of bitter melon under salt stress conditions (0, 50 and 100 mM).

Salt stress, foliar applications and their interaction also had a significant effect on fruit number, fresh and dry, firmness, soluble solids (TSS), length and width, yield, seed number, dry weight and weight of 1000 seeds (p ≤ 0.01) (Table S2). Yield and yield components of bitter melon decreased with increasing salinity stress. The highest fruit number of (19.66), fresh fruit weight (150.66 g), dry fruit weight (8.49 g), firmness (14.78 N), TSS (5.82 ºBrix), fruit length (19.57 cm), fruit width (9.13 cm) and plant yield (2972.0 g plant^− 1) were observed in bitter melon treated with allantoin + serotonin under control conditions. Conversely, the lowest yield and yield components were observed in bitter melon grown under 100 mM NaCl. Under salinity stress conditions, combined application of allantoin and serotonin was the most effective in improving yield and yield components of bitter melon (Table 3).

Table 3.

The effect of different levels of salt stress (0, 50 and 100 mM NaCl), foliar applications (allantoin, serotonin, allantoin+serotonin) and their interaction on quantitative and qualitative characteristics of yield and yield components of bitter melon plant.

Treatment	Number of fruits (-)	Fresh fruit weight (g)	Dry fruit weight (g)	Firmness (N)	TSS (ºBrix)	Fruit length (cm)	Fruit width (cm)	Plant yield (g plant^− 1)	Number of seed (-)	Dry seed weight (g)	Weight of 1000 grains (g)
S₁M₁	16.66 ± 0.19^c	91.00 ± 0.49^bc	5.71 ± 0.38^c	8.77 ± 0.02^d	5.17 ± 0.01^c	15.96 ± 0.05^d	5.43 ± 0.01^cd	1517.0 ± 22.87^bc	30.66 ± 0.19^d	5.27 ± 0.04^d	8325.4 ± 28.15^b
S₁M₂	17.33 ± 0.19b^c	98.47 ± 0.49^b	6.43 ± 0.06^b	10.07 ± 0.15^c	5.24 ± 0.01^c	17.20v0.18^c	5.66 ± 0.09^c	1707.3 ± 25.33^b	33.00 ± 0.33^c	5.87 ± 0.10^c	8362.2 ± 39.20^b
S₁M₃	18.33 ± 0.19^b	101.43 ± 0.48^b	7.00 ± 0.09^b	11.23 ± 0.19^b	5.58 ± 0.02^b	18.80 ± 0.14^b	7.11 ± 0.29^b	1860.2 ± 27.37^b	36.66 ± 0.50^b	7.03 ± 0.01^b	8456.5 ± 60.54^b
S₁M₄	19.66 ± 0.19^a	150.66 ± 11.10^a	8.49 ± 0.10^a	14.78 ± 0.37^a	5.82 ± 0.03^a	19.57 ± 0.15^a	9.13 ± 0.05^a	2972.0 ± 39.21^a	40.33 ± 0.07^a	7.74 ± 0.18^a	9812.4 ± 81.82^a
S₂M₁	10.66 ± 0.19^f	71.42 ± 0.46^de	3.20 ± 0.03^efg	7.14 ± 0.05^gh	4.30 ± 0.02^f	14.16 ± 0.01^fg	4.90 ± 0.00^ef	762.3 ± 18.39^efg	24.66 ± 0.19^f	2.91 ± 0.00^g	5810.3 ± 44.94^d
S₂M₂	12.00 ± 0.33^e	73.55 ± 0.25^cde	3.36 ± 0.11^e	7.43 ± 0.00^fg	4.60 ± 0.03^e	14.60 ± 0.08^f	4.96 ± 0.01^def	883.1 ± 27.17^def	25.00 ± 0.00^f	3.55 ± 0.18^f	5814.0 ± 35.85^d
S₂M₃	14.00 ± 0.00^d	77.38 ± 0.66^cd	3.77 ± 0.02^e	7.95 ± 0.13^ef	4.86 ± 0.03^d	15.10 ± 0.00^e	5.10 ± 0.03^de	1083.4 ± 9.32^de	25.33 ± 0.19^f	4.36 ± 0.03^e	7145.9 ± 2.87^c
S₂M₄	14.33 ± 0.19^d	85.05 ± 1.57^bcd	4.55 ± 0.01^d	8.57 ± 0.06^de	5.07 ± 0.01^cd	15.43 ± 0.05^e	5.30 ± 0.03^cde	1220.7 ± 38.20^cd	28.33 ± 0.69^e	4.89 ± 0.06^d	8232.3 ± 44.75^b
S₃M₁	5.66 ± 0.38^h	44.18 ± 1.57^g	2.55 ± 0.04^g	5.61 ± 0.02^j	3.36 ± 0.13^h	12.16 ± 0.06^j	4.23 ± 0.01^g	253.1 ± 24.91^h	20.00 ± 0.00ⁱ	2.05 ± 0.06^h	5212.5 ± 34.51^d
S₃M₂	9.00 ± 0.00^g	50.57 ± 0.76^fg	2.69 ± 0.00^fg	5.88 ± 0.04^ij	3.98 ± 0.01^g	12.76 ± 0.01ⁱ	4.46 ± 0.01^fg	455.1 ± 6.78^gh	21.00 ± 0.33hⁱ	2.55 ± 0.02^g	5213.6 ± 61.34^d
S₃M₃	9.00 ± 0.00^g	55.66 ± 1.01^efg	2.76 ± 0.00^fg	6.45 ± 0.03^hi	4.10 ± 0.01^fg	13.26 ± 0.08^h	4.53 ± 0.01^fg	501.0 ± 9.16^fgh	22.33 ± 0.19^gh	2.68 ± 0.03^g	5622.6 ± 32.51^d
S₃M₄	10.00 ± 0.00^fg	67.21 ± 0.51^def	2.91 ± 0.00^fg	6.75 ± 0.05^gh	4.17 ± 0.01^fg	13.83 ± 0.09^g	4.80 ± 0.00^ef	672.1 ± 5.10^fg	23.66 ± 0.19f^g	2.83 ± 0.00^g	5784.3 ± 52.09^d

Open in a new tab

Physiological characteristics

Photosynthetic pigments

Analysis of variance revealed that the main effects of salt stress, foliar application, and their interaction significantly influenced all measured photosynthetic parameters. This included chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, the fluorescence parameter Fv/Fm, and performance index (PI_ABS) (all at p ≤ 0.01), as well as the SPAD index (p ≤ 0.05) (Table S3). Salt stress decreased the amount of chlorophyll a, chlorophyll b and total chlorophyll in bitter melon leaves. The highest amount of chlorophyll a (19.99 mg g^− 1 FW), chlorophyll b (8.62 mg g^− 1 FW), total chlorophyll (28.61 mg g^− 1 FW), carotenoid (5.35 mg g^− 1 FW), Fv/Fm (0.84), PI (17.93) and SPAD (34.10) was observed in the treatment of allantoin + serotonin under control conditions. The combined foliar application of allantoin and serotonin resulted in a significant increase in photosynthetic pigments, performance index (PI_ABS), SPAD values, and the Fv/Fm ratio across all salinity stress levels when compared to the untreated control (Table 4).

Table 4.

The effect of different levels of salt stress (0, 50 and 100 mM NaCl), foliar applications (allantoin, serotonin, allantoin+serotonin) and their interaction on chlorophyll a, chlorophyll b and total chlorophyll, carotenoid, chlorophyll fluorescence parameter (Fv/Fm), PI_ABS and SPAD of bitter melon leaves.

Treatment	Chlorophyll a (mg g FW^− 1)	Chlorophyll b (mg g FW^− 1)	Total chlorophyll (mg g FW^− 1)	Carotenoid (mg g FW^− 1)	Chlorophyll fluorescence (Fv/Fm)	PI_ABS (-)	SPAD (-)
S₁M₁	15.38 ± 0.13^d	5.51 ± 0.03^cd	20.90 ± 0.17^d	3.73 ± 0.07^d	0.79 ± 0.00^cd	12.29 ± 0.08^d	30.76 ± 0.16^d
S₁M₂	16.99 ± 0.23^c	5.93 ± 0.06^c	22.92 ± 0.30^c	4.14 ± 0.05^c	0.81 ± 0.00^bc	13.68 ± 0.17^c	31.96 ± 0.16^c
S₁M₃	18.34 ± 0.16^b	7.08 ± 0.16^b	25.42 ± 0.32^b	4.42 ± 0.01^b	0.82 ± 0.00^b	16.50 ± 0.27^b	33.03 ± 0.17^b
S₁M₄	19.99 ± 0.22^a	8.62 ± 0.24^a	28.61 ± 0.46^a	5.35 ± 0.01^a	0.84 ± 0.00^a	17.93 ± 0.23^a	34.10 ± 0.13^a
S₂M₁	12.87 ± 0.03^fg	4.71 ± 0.00^fg	17.58 ± 0.04^fg	3.00 ± 0.00^g	0.74 ± 0.00^e	9.29 ± 0.10^fg	28.03 ± 0.05^g
S₂M₂	13.13 ± 0.01^fg	4.82 ± 0.01^efg	17.96 ± 0.03^fg	3.10 ± 0.00^fg	0.77 ± 0.00^d	9.98 ± 0.04^f	28.80f ± 0.03^g
S₂M₃	13.52 ± 0.09^ef	4.98 ± 0.04^ef	18.50 ± 0.13^ef	3.17 ± 0.00^f	0.78 ± 4.53^d	10.92 ± 0.16^e	29.10e ± 0.06^f
S₂M₄	13.91 ± 0.04^e	5.22 ± 0.01^de	19.13 ± 0.05^e	3.41 ± 0.00^e	0.78 ± 0.00^d	11.75 ± 0.08^d	29.80 ± 0.14^e
S₃M₁	10.45 ± 0.18^j	4.02 ± 0.04ⁱ	14.47 ± 0.22^j	2.14 ± 0.01^k	0.60 ± 0.00ⁱ	6.20 ± 0.14^j	23.03 ± 0.16^k
S₃M₂	11.61 ± 0.09ⁱ	4.20 ± 0.00^hi	15.81 ± 0.09ⁱ	2.36 ± 0.02^j	0.62 ± 0.00^h	7.34 ± 0.07ⁱ	24.33 ± 0.24^j
S₃M₃	12.04 ± 0.06^hi	4.37 ± 0.02^ghi	16.41 ± 0.09^hi	2.60 ± 0.00ⁱ	0.68 ± 0.00^g	8.42 ± 0.02^h	25.56 ± 0.12ⁱ
S₃M₄	12.55 ± 0.07^gh	4.60 ± 0.04^fgh	17.16 ± 0.12^gh	2.78 ± 0.03^h	0.79 ± 0.00^f	8.69 ± 0.04^gh	27.06 ± 0.26^h

Open in a new tab

Relative water content (RWC), electrolyte leakage (EL) and stomatal resistance

According to the analysis of variance (Table S4), salt stress, foliar applications and their interaction had a significant effect on RWC, EL and stomatal resistance of bitter melon leaves (p ≤ 0.01). Based on the results obtained, salinity decreased RWC of the leaves. The highest amount of RWC (80.40%) was recorded in bitter melon treated with allantoin + serotonin under salt stress conditions. In contrast to salinity, allantoin and serotonin decreased the rate of EL and stomatal resistance. The highest EL and stomatal resistance were observed in 100 mM NaCl treated bitter melons. The lowest EL (33.52%) and stomatal resistance (6.13 mmol/m²s) were recorded in allantoin + serotonin-treated plants under control conditions (Table 5).

Table 5.

The effect of different levels of salt stress (0, 50 and 100 mM NaCl), foliar applications (allantoin, serotonin, allantoin+serotonin) and their interaction on RWC, EL and stomatal resistance of bitter melon leaves.

Treatment	RWC (%)	EL (%)	Stomatal resistance (mmol/m²s)
S₁M₁	67.67 ± 0.11^cd	43.51 ± 0.11^e	8.03 ± 0.11^ghi
S₁M₂	69.80 ± 0.92^c	40.11 ± 0.06^f	7.53 ± 0.03^hij
S₁M₃	74.64 ± 0.85^b	37.88 ± 0.34^g	6.83 ± 0.05^ij
S₁M₄	80.40 ± 0.73^a	33.52 ± 0.72^h	6.13 ± 0.12^j
S₂M₁	61.57 ± 0.47^ef	48.86 ± 0.34^d	11.00 ± 0.00^de
S₂M₂	63.38 ± 0.05^e	47.89 ± 0.00^d	9.83 ± 0.09^ef
S₂M₃	65.84 ± 0.11^d	47.49 ± 0.08^d	9.33 ± 0.01^fg
S₂M₄	66.58 ± 0.04^d	44.76 ± 0.17^e	8.80 ± 0.08^fgh
S₃M₁	52.17 ± 0.05ⁱ	60.48 ± 0.59^a	19.96 ± 1.00^a
S₃M₂	57.47 ± 0.05^h	56.60 ± 0.40^b	15.03 ± 0.10^b
S₃M₃	58.96 ± 0.32^gh	55.04 ± 0.01^b	13.53 ± 0.15^bc
S₃M₄	60.19 ± 0.08^fg	50.69 ± 0.06^c	12.53 ± 0.16^cd

Open in a new tab

Antioxidant compounds and capacity, compatible metabolites, ascorbic acid, ABA and soluble proteins

Proline and total soluble sugar content were significantly affected by salt stress, foliar application, and their interaction), total phenols and flavonoids, anthocyanins (antioxidant compounds), antioxidant capacity, ascorbic acid, ABA and soluble proteins (Table S5). Proline, total soluble sugars, soluble protein, total phenols and flavonoids, anthocyanins and antioxidant capacity content in the leaves of bitter melon increased with increase in salinity level, reaching the highest contents at 100 mM NaCl. The application of allantoin and serotonin positively influenced proline, total soluble sugars, soluble proteins, total phenols and flavonoids, anthocyanins and antioxidant capacity content of bitter melon under salt stress conditions. In specific, the highest amount of proline (28.38 μm g^− 1), total soluble sugars (6.39 mg g^− 1), soluble proteins (6.83%), total phenols (33.91 mg g^− 1 FW), total flavonoids (10.01 mg g^− 1 FW), anthocyanins (1.97 mg g^− 1 FW), antioxidant capacity (44.85%) and ABA (55.34 ng g^− 1 FW) content were recorded in allantoin + serotonin treated plants under 100 mM NaCl (Table 6). Salinity reduced ascorbic acid content while allantoin and serotonin reversed the effect. The highest amount of ascorbic acid (22.49 mg 100 g^− 1) was observed in the allantoin + serotonin-treated plants under control conditions. In addition, allantoin + serotonin increased the amount of ascorbic acid in bitter melon leaves in all three levels of salinity stress (Table 6).

Table 6.

The effect of different levels of salt stress (0, 50 and 100 mM NaCl), foliar applications (allantoin, serotonin, allantoin+serotonin) and their interaction on proline, total soluble sugars, soluble proteins, total phenols, total flavonoids, anthocyanins, antioxidant capacity based on DPPH, ascorbic acid and ABA of bitter melon leaves.

Treatment	Proline (µm g^− 1)	Total soluble sugars (mg g^− 1)	Soluble protein (%)	Total phenol (mg g^− 1 FW)	Total flavonoid (mg g^− 1 FW)	Anthocyanin (mg g^− 1)	DPPH (%)	Ascorbic acid (mg 100 g^− 1 FW)	ABA (ng g^− 1)
S₁M₁	14.54 ± 0.11^j	3.06 ± 0.03^l	4.11 ± 0.02ⁱ	16.19 ± ± 0.10ⁱ	5.34 ± 0.08^k	1.08 ± 0.02^j	27.84 ± 0.24ⁱ	16.46 ± 0.06^d	30.10 ± 0.07ⁱ
S₁M₂	15.17 ± 0.10^j	3.54 ± 0.01^k	4.56 ± 0.11^h	16.99 ± 0.09^hi	5.81 ± 0.04^j	1.20 ± 0.00ⁱ	28.87 ± 0.13^hi	18.35 ± 0.20^c	31.81 ± 0.07^h
S₁M₃	15.65 ± 0.06^ij	3.83 ± 0.03^j	5.06 ± 0.01^g	17.55 ± 0.07^ghi	6.11 ± 0.03ⁱ	1.28 ± 0.01^h	30.03 ± 0.24^h	20.12 ± 0.32^b	32.51 ± 0.15^h
S₁M₄	16.66 ± 0.01^hi	4.12 ± 0.03ⁱ	5.17f ± 0.00^g	18.04 ± 0.02^fgh	6.64 ± 0.07^h	1.38 ± 0.00^g	32.10 ± 0.21^g	22.49 ± 0.10^a	33.52 ± 0.05^gh
S₂M₁	17.37 ± 0.17^gh	4.54 ± 0.03^h	5.33 ± 0.02^ef	18.44 ± 0.07^fgh	7.02 ± 0.04^g	1.42 ± 0.00^g	33.26 ± 0.11^g	14.72 ± 0.06^gh	34.25 ± 0.09^g
S₂M₂	18.45 ± 0.25^fg	4.78 ± 0.00^g	5.50 ± 0.03^e	19.10 ± 0.07^efg	7.41 ± 0.04^f	1.48 ± 0.00^f	34.51 ± 0.21^f	15.14 ± 0.08^fg	36.63 ± 0.42^f
S₂M₃	19.75 ± 0.13^ef	5.01 ± 0.01^f	5.86 ± 0.02^d	19.77 ± 0.07^def	7.87 ± 0.03^e	1.53 ± 0.00^e	36.21 ± 0.28^e	15.60 ± 0.03^ef	41.46 ± 0.37^e
S₂M₄	20.92 ± 0.17^de	5.22 ± 0.03^e	6.06 ± 0.00^cd	20.33 ± 0.03^ed	8.11 ± 0.03^e	1.57 ± 0.00^e	37.78 ± 0.29^d	16.05 ± 0.07^de	42.95 ± 0.16^de
S₃M₁	22.17 ± 0.22^cd	5.47 ± 0.03^d	6.16 ± 0.03^c	21.02 ± 0.15^d	8.65 ± 0.07^d	1.64 ± 0.01^d	40.02 ± 0.10^c	13.08 ± 0.03^k	44.30 ± 0.34^d
S₃M₂	23.45 ± 0.06^bc	5.88 ± 0.03^c	6.44 ± 0.01^b	26.79 ± 1.00^c	9.03 ± 0.04^c	1.74 ± 0.01^c	41.07 ± 0.26^c	13.50 ± 0.08^jk	49.28 ± 0.66^c
S₃M₃	24.60 ± 0.24^b	6.11 ± 0.05^b	6.56 ± 0.03^b	31.66 ± 0.19^b	9.39 ± 0.03^b	1.83 ± 0.01^b	43.28 ± 0.37^b	13.91 ± 0.06^ji	52.22 ± 0.29^b
S₃M₄	28.38 ± 0.77^a	6.39 ± 0.03^a	6.83 ± 0.03^a	33.91 ± 0.34^a	10.01 ± 0.10^a	1.97 ± 0.01^a	44.85 ± 0.11^a	14.37 ± 0.02^hi	55.34 ± 0.45^a

Open in a new tab

Antioxidant enzymes (CAT, POX, SOD, APX), MDA and H₂O₂

Our data demonstrate a significant effect of salt stress, the application of biostimulants (the moderator), and the interaction between these factors on key oxidative stress parameters in bitter melon leaves, including the activities of catalase (CAT), peroxidase (POX), superoxide dismutase (SOD), and ascorbate peroxidase (APX), as well as malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content (p ≤ 0.01) (Table S6). Allantoin and serotonin application mostly enhanced the enzymes activities under control and salinity conditions. As the salinity level increased from 0 to 100 mM NaCl concentrations, the activity of catalase (CAT), peroxidase (POX), superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzymes increased. The highest activity levels of catalase (CAT) (10.09 IU g^− 1), peroxidase (POX) (4.83 IU g^− 1), superoxide dismutase (SOD) (6.20 IU g^− 1) and ascorbate peroxidase (APX) (3.90 IU g^− 1) were observed in allantoin + serotonin treated plants under the highest salinity level (Fig. 2a). According to the obtained results, unlike allantoin and serotonin, salinity increased the content of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) with the highest content of malondialdehyde (MDA) (8.77 µ mol g^− 1) and hydrogen peroxide (H₂O₂) (5.40 µ mol g^− 1) to be recorded at 100 mM NaCl. Allantoin, serotonin and their combined application reduced malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) under control and salinity conditions and their lowest content was obtained in allantoin + serotonin treated plants under control conditions (Fig. 2b).

Fig. 2 — The effect of different levels of salt stress (0, 50 and 100 mM NaCl), foliar applications (allantoin, serotonin, allantoin+serotonin) and their interaction on CAT. POX, SOD, APX (a), MDA, H₂O₂ (b). S₁, S₂ and S₃ are 0, 50 and 100 mM NaCl; M₁, M₂, M₃ and M₄ are control, allantoin (1000 µM), serotonin (100 µM) and allantoin+serotonin.

Leaf K, Na, P and Cl concentration

The results indicated that both salt stress and foliar application significantly influenced the concentration of nutritional elements (i.e., K, Na, P, Cl and N) of bitter melon leaf (p ≤ 0.01) (Table S7). Likewise, the interaction effect was significant on all mentioned elements; K, P and Cl⁻ (p ≤ 0.01), Na and N (p ≤ 0.05) (Table S7). The results indicated that leaf potassium (K) and phosphorus (P) concentrations decreased progressively with increasing salinity. However, the application of allantoin and serotonin significantly increased the content of these elements under salt stress conditions. The highest amounts of Na (51.61 mg 100 g DW^− 1) and Cl (8.49 mg g DW^− 1) in leaf were observed in 100 mM NaCl. On the other hand, the highest amount of K (2015.7 mg 100 g^− 1) and P (980.00 mg 100 g DW^− 1) was found in allantoin + serotonin treated plants under control conditions. Unlike salt stress that reduced N content, the application of modifiers increased the amount of N under control and salinity conditions reaching the highest amount (4459.0 mg 100 g DW^− 1) in allantoin + serotonin treated plants under control conditions (Table 7).

Table 7.

The mean comparison of the effect of different levels of salt stress (0, 50 and 100 mM NaCl), foliar applications (allantoin, serotonin, allantoin+serotonin) and their interaction on leaf K⁺, Na⁺, P, Cl⁻ and N content of bitter melon leaf.

Treatment	K (mg 100 g DW^− 1)	Na (mg 100 g DW^− 1)	P (mg 100 g DW^− 1)	Cl (mg g DW^− 1)	N (mg 100 g DW^− 1)
S₁M₁	1279.0 ± 15.58^cd	36.83 ± 0.12^h	765.67 ± 4.85^d	5.36 ± 0.06^g	3277.3 ± 10.67^d
S₁M₂	1490.3 ± 12.07^bc	35.93 ± 0.18^hi	841.67 ± 6.66^c	4.94 ± 0.09^h	3511.7 ± 42.41^c
S₁M₃	1617.3 ± 23.62^b	35.05 ± 0.04^ij	900.00 ± 6.42^b	4.54 ± 0.02ⁱ	3995.3 ± 24.94^b
S₁M₄	2015.7 ± 16.48^a	33.96 ± 0.28^j	980.00 ± 4.05^a	4.17 ± 0.02^j	4459.0 ± 59.07^a
S₂M₁	982.3 ± 0.83^efg	42.17 ± 0.18^e	613.00 ± 3.92^g	6.87 ± 0.01^d	2600.7 ± 38.20^ef
S₂M₂	999.3 ± 3.33^efg	41.16 ± 0.08^ef	651.33 ± 6.71^f	6.59 ± 0.01^d	2713.0 ± 9.83^e
S₂M₃	1109.7 ± 31.62^def	40.11 ± 0.20^f	705.67 ± 4.85^e	6.21 ± 0.07^e	2805.3 ± 34.92^e
S₂M₄	1217.3 ± 0.76^de	38.21 ± 0.23^vg	730.67 ± 3.00^e	5.83 ± 0.02^f	3083.0 ± 42.24^d
S₃M₁	826.7 ± 8.38^g	51.61 ± 0.58^a	410.67 ± 3.67^k	8.49 ± 0.09^a	1579.7 ± 99.68ⁱ
S₃M₂	884.7 ± 1.17^fg	48.17 ± 0.39^b	478.00 ± 15.67^j	8.03 ± 0.03^b	20.65.0 ± 17.03^h
S₃M₃	903.3 ± 5.09^fg	46.12 ± 0.16^c	523.00 ± 0.33ⁱ	7.80 ± 0.01^b	2282.0 ± 17.92^g
S₃M₄	948.0 ± 3.52^efg	43.83 ± 0.14^d	570.67 ± 6.00^h	7.30 ± 0.07^c	2393.3f ± 9.37^g

Open in a new tab

Secondary metabolites content

Salt stress and foliar applications significantly influenced on the secondary metabolites of bitter melon fruit (p ≤ 0.01), alkaloid, ascorbic acid, saponin, momordicin, momordicozide and momordin (p ≤ 0.01), total soluble sugars and charantin (p ≤ 0.05) (Table S8). Contrary to salinity, foliar spraying of modifiers positively affected on alkaloid, ascorbic acid, saponin, momordicin, momordicozide and momordin content of bitter melon fruit. The highest amount of alkaloid (139.33 mg 100 g^− 1), total soluble sugar (29.47 mg g^− 1), saponin (160.37 mg 100 g^− 1), were observed in the highest concentration of salinity treated with allantoin + serotonin (Table 8). The highest amount of charantin (795.10 µg 100 g^− 1), momordicin (526.60 µg 100 g^− 1), momordicozide (349.00 µg 100 g^− 1) and momordin (488.33 µg 100 g^− 1) were observed in allantoin + serotonin treated plants under 50 mM NaCl. At the concentration of 100 mM salt stress, the amount of secondary compounds of bitter melon fruit decreased reaching lower content than the control (Table 8). In the present study, a significant decrease in the amount of ascorbic acid in bitter melon was observed with increasing NaCl. Foliar application of modifiers increased the amount of ascorbic acid when bitter melon fruit was exposed to 100 mM NaCl (Table 8).

Table 8.

The effect of different levels of salt stress (0, 50 and 100 mM NaCl), foliar applications (allantoin, serotonin, allantoin+serotonin) and their interaction on alkaloid, ascorbic acid, saponin, total soluble sugars and charantin, momordicin, momordicozide and momordin of bitter melon fruit.

Treatment	Alkaloid (mg 100 g^− 1)	Ascorbic acid (mg 100 g^− 1)	Saponin (mg 100 g^− 1)	Total soluble sugar (mg g^− 1)	Charantin (µg 100 g^− 1)	Momordicin (µg 100 g^− 1)	Momordicozide (µg 100 g^− 1)	Momordin (µg 100 g^− 1)
S₁M₁	89.84 ± 0.51^l	93.24 ± 0.19^c	106.13 ± 1.79^h	10.49 ± 0.08ⁱ	658.31 ± 1.23^g	428.00 ± 0.033^g	263.33 ± 1.17^g	386.00 ± 1.52^e
S₁M₂	94.20 ± 0.52^k	95.28 ± 0.41^b	110.60 ± 0.36^gh	11.03 ± 0.07ⁱ	673.62 ± 2.94^f	431.33 ± 1.07^g	273.00 ± 2.02^f	397.00 ± 0.88^e
S₁M₃	97.52 ± 0.60^j	97.77 ± 0.16^a	114.10 ± 0.48^g	11.40 ± 0.03ⁱ	692.77 ± 1.89^e	430.00 ± 0.33^f	290.00 ± 0.13^e	413.33 ± 0.76^d
S₁M₄	102.24 ± 0.66ⁱ	98.64 ± 0.11^a	118.74 ± 0.48^f	12.91 ± 0.19^h	704.85 ± 1.76^e	449.00 ± 0.57^e	306.66 ± 1.92^d	426.66 ± 1.07^c
S₂M₁	107.90 ± 0.19^h	82.98 ± 0.24^g	122.24 ± 0.32^f	16.05 ± 0.66^g	722.92 ± 2.85^d	484.33 ± 1.34^d	318.00 ± 2.08^c	432.00 ± 0.33^c
S₂M₂	112.46 ± 0.88^g	84.81 ± 0.22^f	128.26v0.46^e	17.78 ± 0.15^f	737.17 ± 2.07^c	495.81 ± 1.75^c	324.00 ± 0.57^c	453.33 ± 2.83^b
S₂M₃	119.10 ± 0.35^f	87.51 ± 0.33^e	131.29 ± 0.49^e	19.47 ± 0.18^e	773.12 ± 5.46^b	515.8 ± 1.40^b	337.66 ± 2.91^b	477.66 ± 0.38^a
S₂M₄	125.21 ± 0.90^e	90.33 ± 0.31^d	136.49 ± 0.92^d	21.99 ± 0.18^d	795.10 ± 0.94^a	526.60 ± 2.02^a	349.00 ± 1.20^a	488.33 ± 3.02^a
S₃M₁	129.74 ± 0.55^d	71.92 ± 0.56^k	141.45 ± 0.70^c	23.71 ± 0.25^c	602.63 ± 0.70^j	405.65 ± 1.68ⁱ	224.33 ± 3.28ⁱ	310.00 ± 3.33ⁱ
S₃M₂	132.72 ± 0.33^c	75.26 ± 0.27^j	145.63 ± 0.64^c	24.84 ± 0.11^c	611.86 ± 1.01^ij	410.81 ± 0.20ⁱ	234.66 ± 0.38^h	325.66 ± 1.34^h
S₃M₃	136.29 ± 0.55^b	77.73 ± 0.30ⁱ	153.77 ± 1.04^b	27.12 ± 0.20^b	622.96 ± 2.14ⁱ	411.53 ± 0.07ⁱ	243.00 ± 2.02^h	342.66 ± 3.74^g
S₃M₄	139.33 ± 0.21^a	80.34 ± 0.39^h	160.37 ± 1.52^a	29.47 ± 0.25^a	635.43 ± 2.53^h	421.83 ± 0.55^h	256.00 ± 0.57^g	373.00 ± 3.05^f

Open in a new tab

Coumaric acid, furic acid, caffeic acid, gallic acid and cinnamic acid content

The data of the present study demonstrated a highly significant effect (p ≤ 0.01) of the main factors—salinity, biostimulant application—and their synergistic interaction on the accumulation of specific phenolic compounds in the fruit, including p-coumaric, ferulic, caffeic, gallic, and cinnamic acids (Table S9). The results of the present study clearly indicated that salinity enhanced the phenolic content; the higher salinity levels the higher phenolic acids concentrations, compared to the control. Application of allantoin and serotonin increased the amount of phenolic acids (Table 9). In fruit, the highest amount of p-coumaric acid (24.01 µg g DW^− 1), ferulic acid (11.72 µg g DW^− 1), caffeic acid (17.22 µg g DW^− 1), gallic acid (9.85 µg g DW^− 1) and cinnamic acid (8.76 µg g DW^− 1) was observed in allantoin + serotonin treated plants under the highest concentration of salinity (100 mM) (Table 9). In the leaf and fruit, at all three salinity levels, the modifiers increased the amount of phenolic acids (Table 9).

Table 9.

Results of comparison of the average effect different levels of salt stress and coumaric acid, ferulic acid, caffeic acid, gallic acid and cinnamic acid.

Treatment	p-coumaric acid (µg g DW^− 1)	Ferulic acid (µg g DW^− 1)	Caffeic acid (µg g DW^− 1)	Gallic acid (µg g DW^− 1)	Cinnamic acid (µg g DW^− 1)
			Leaf
S₁M₁	6.28 ± 0.06^k	11.16 ± 0.04^j	6.16 ± 0.01ⁱ	8.21 ± 0.09ⁱ	3.15 ± 0.05^k
S₁M₂	6.61 ± 0.01^j	11.66 ± 0.07ⁱ	6.33 ± 0.02ⁱ	8.82 ± 0.04^h	3.67 ± 0.03^j
S₁M₃	6.95 ± 0.05ⁱ	12.04 ± 0.03^h	6.77 ± 0.07^h	9.53 ± 0.09^g	4.00 ± 0.06ⁱ
S₁M₄	7.20 ± 0.01^h	12.33 ± 0.03^g	7.13 ± 0.03^h	10.02 ± 0.05^fg	4.34 ± 0.03^h
S₂M₁	7.50 ± 0.01^g	12.76 ± 0.03^f	7.3 ± 0.03^g	10.53 ± 0.10^f	4.53 ± 0.03^g
S₂M₂	7.74 ± 0.02^f	13.04 ± 0.02^e	7.70 ± 0.05^f	11.28 ± 0.10^e	4.89 ± 0.00^f
S₂M₃	7.86 ± 0.02^f	13.32 ± 0.05^d	8.08 ± 0.02^e	11.79 ± 0.03^de	5.03 ± 0.01^ef
S₂M₄	8.11 ± 0.02^e	13.54 ± 0.01^d	8.21 ± 0.00^e	11.97 ± 0.02^d	5.12 ± 0.02^de
S₃M₁	8.36 ± 0.05^d	13.94 ± 0.05^c	8.56 ± 0.07^d	12.28 ± 0.05^d	5.30 ± 0.02^d
S₃M₂	8.85 ± 0.02^c	14.15 ± 0.03^c	9.00 ± 0.06^c	13.14 ± 0.21^c	5.53 ± 0.04^c
S₃M₃	9.05 ± 0.01^b	14.55 ± 0.07^b	9.45 ± 0.06^b	13.79 ± 0.01^b	5.76 ± 0.03^b
S₃M₄	9.31 ± 0.05^a	15.10 ± 0.03^a	9.77 ± 0.03^a	14.52 ± 0.18^a	5.96 ± 0.01^a
			Fruit
S₁M₁	14.21 ± 0.09^k	5.31 ± 0.03^k	7.78 ± 0.77ⁱ	4.10 ± 0.00^l	4.03 ± 0.01^j
S₁M₂	14.77 ± 0.07^j	5.82 ± 0.04^j	9.67 ± 0.06^h	4.50 ± 0.04^k	4.44 ± 0.07ⁱ
S₁M₃	15.24 ± 0.06ⁱ	6.17 ± 0.04^j	10.40 ± 0.11^gh	5.02 ± 0.07^j	5.03 ± 0.04^h
S₁M₄	15.71 ± 0.04^h	6.76 ± 0.05ⁱ	11.03 ± 0.01^fg	5.67 ± 0.07ⁱ	5.28 ± 0.03^h
S₂M₁	16.09 ± 0.01^h	7.34 ± 0.03^h	11.87 ± 0.06^ef	6.17 ± 0.04^h	5.67 ± 0.08^g
S₂M₂	16.76 ± 0.18^g	8.11 ± 0.12^g	12.33 ± 0.07^ed	6.64 ± 0.03^g	6.22 ± 0.08^f
S₂M₃	17.68 ± 0.06^f	8.56 ± 0.06^f	13.08 ± 0.04^cde	7.06 ± 0.05^f	6.65 ± 0.03^e
S₂M₄	18.38 ± 0.05^e	9.14 ± 0.06^e	13.56 ± 0.03^bcd	7.76 ± 0.07^e	6.94 ± 0.02^d
S₃M₁	19.57 ± 0.06^d	9.74 ± 0.06^d	14.10v0.07^bc	8.12 ± 0.02^d	7.18 ± 0.09^d
S₃M₂	20.48 ± 0.07^c	10.26 ± 0.07^c	14.60 ± 0.04^b	8.55 ± 0.07^c	7.55 ± 0.00^c
S₃M₃	22.29 ± 0.12^b	10.85 ± 0.10^b	16.25 ± 0.23^a	9.22 ± 0.07^b	8.07 ± 0.04^b
S₃M₄	24.01 ± 0.02^a	11.72 ± 0.09^a	17.22 ± 0.07^a	9.85 ± 0.01^a	8.76 ± 0.03^a

Open in a new tab

Tables S10 and S11 reveals that each principal component is separately loaded with various morphological and physiochemical traits under investigation known as factor loadings. Factor loadings represent the relationship between the original variables and the principal components. These values indicate how strongly each variable contributes to or correlates with a specific principal component. Confirmation of grouping based on principal components also showed that the first and second two components contributed 86.68 and 9.14) to the confirmation of groupings, respectively.

PCA provided a comprehensive overview of the effects of biostimulants growth and biochemical characteristics activity under NaCl stress (Fig. 3). The biplot (Fig. 3) typically displays the first two principal components (PC1 and PC2) as the axes, as these components capture the most of the variability. In grouping the studied treatments based on principal component analysis, the grouping results showed that the studied treatments were placed in separate groups based on the studied traits (Fig. 3). The results of this grouping showed that, based on the principal components, traits such as stomatal resistance, Na, Cl, EL, and MDA were included in the S2M1, S2M2 and S3M1 treatment groups. Also, the fruit dry weight and carotenoids are related to treatments S1M1 and S1M2. Biochemical characteristics were in treatment group S1M3, S1M4 and S2M4 (Fig. 3).

Fig. 3 — Two-dimensional diagram of principal component analysis in grouping treatments and studied traits in bitter melon plant.

Discussion

The escalating demand for food is severely threatened by salt stress, a major issue in the world’s arid and semiarid zones⁶⁰. In this study, salt stress restricted bitter melon growth and yield. Similar results were obtained in tomato (Solanum lycopersicum L.)⁶¹, lettuce (Lactuca sativa L.)⁶² and cucumber (Cucumis sativus L.)⁶³. Salt-induced plant growth decrease could be attributed to impaired water⁶⁴ and nutrient absorption, disrupted ion homeostasis and osmotic adjustment, altered soil water potential, and inhibition of photosynthetic efficacy^62,65. Accumulation of Na in the aerial plant parts and reduced cellular turgor and cell elongation⁶⁶ contribute to reduced growth and consequential decrease in lateral branching⁶⁷. The observed reversal of salt stress effects on plant growth with the combined foliar application of allantoin and serotonin, identified as the most effective treatment, suggests a potential synergistic interaction. This positive outcome could be attributed to their combined hormonal and signaling roles in regulating growth-related processes. As a N source, allantoin may improve salt tolerance through the upregulation of reactive oxygen species (ROS) scavenging systems, the preservation of ion homeostasis, and the enhancement of osmotic adjustment^68,69. The increased accumulation of allantoin in plants during stress conditions indicates its important role in stress modulation⁷⁰. In the present study, allantoin regulated salt tolerance mechanism in bitter melon seedlings via improved growth and yield characteristics, in agreement with previous reports in sugar beet (Beta vulgaris L.), Arabidopsis (Arabidopsis thaliana L.) and rice (Oryza sativa L.)^23,26,71. A possible mechanism is the NH₄⁺ increase via allantoin catabolism that contributes to N homeostasis acting as a signaling molecule^24,72. The application of serotonin effectively mitigated the detrimental impacts of salt stress and enhanced the growth of bitter melon plants. This finding aligns with the work of Arya et al⁷³, who suggested that the underlying mechanism may involve the modulation of gene expression in auxin-responsive pathways, a concept previously supported by⁷⁴. Serotonin exhibits a cytokinin-like activity, essential for cell division promotion and antioxidative stress protection, all leading to promoted growth of salt-stressed bitter melon⁷⁵, as already found in sunflower (Helianthus annuus L.)³⁴. Our study’s positive effect of foliar serotonin application on salinity, likely via scavenging ROS and osmotic pressure regulation⁵, is further supported by its ability to mediate the influx of ions into the chloroplasts⁷⁶ and enhanced chlorophyll biosynthesis^12,31. The application of allantoin and serotonin had a positive effect on the quality characteristics and yield of bitter melon fruit compared to the control.

In this study, the content of photosynthetic pigments, chlorophyll index (SPAD) and chlorophyll fluorescence (Fv/Fm) were significantly declined under salt stress conditions, as previously found in chili pepper⁷⁷ and cucumber⁷⁸. This decline can likely be attributed to a combination of factors, including ROS accumulation, structural damage to chloroplasts and thylakoid membranes, and an energy imbalance caused by stomatal closure limiting CO₂ fixation. Furthermore, impaired water translocation, as indicated by reduced RWC, likely restricted mineral nutrient uptake, exacerbating the negative effects on the photosynthetic apparatus^{3,12,23,30,79}. The application of allantoin and serotonin, individually and in combination, led to increases in SPAD index and Fv/Fm as well as photosynthetic pigments in bitter melon leaves under salt stress conditions. Allantoin has been known to play function in N metabolism and transport¹³ therefore, its positive effect in photosynthetic pigments; SPAD and Fv/Fm could be justified. Similarly, results were found in salt-stressed zinnia (Zinnia elegans L.) plants⁶. Nitrogen serves as a fundamental constituent of nucleotides and proteins, which are essential for photosynthetic efficiency and the activity of critical enzymes⁸⁰. Research on pea chloroplasts indicates that serotonin can enhance the flux of magnesium and calcium, thereby contributing to the protection of photosynthetic tissues²⁹. As a metabolic precursor to melatonin, serotonin may improve photosynthetic performance through analogous pathways. These mechanisms include: 1) elevating photosynthetic pigment and carotenoid levels to bolster antioxidant capacity and protect photosystem II efficiency (Fv/Fm)^12,81 augmenting net photosynthetic rate (Pn) via the modulation of stomatal conductance⁸²preserving chlorophyll by suppressing the expression of genes responsible for its degradation under stress⁸³.

Salt-stressed plants commonly experience intracellular water deficit¹¹, as observed in the current study, evidenced by reduced RWC. Similar results were also observed in cucumber⁶³ and tomato⁷⁰. In the present study allantoin and serotonin application improved RWC²³, maintaining cell turgor²². Allantoin can improve osmoregulation and nutrient uptake, which helps to prevent cellular dehydration under abiotic stress¹³. Increase in RWC by serotonin application might be due to higher root growth that improves water uptake¹².

Salinity leads to enhanced EL and MDA content due to damages to membrane integrity^7,64,84. By improving osmoregulation and nutrient uptake, allantoin helps protect cells from dehydration caused by environmental stresses^12,23. Moreover, exogenous allantoin reduced EL values in salt-stressed plants in our experiment thanks to its intermediate role in ureide metabolism²².

One way to deal with salinity-induced water deficit is reduced stomatal conductance⁸⁵. Decreased stomatal conductance (increased stomatal resistance) under salt stress conditions has also been reported in maize⁸⁶ and tomato⁸⁷. In this study application of allantoin and serotonin, unlike salt stress, reduced stomatal resistance of bitter melon leaves. This could be attributed to the positive effect on N metabolism in plant root growth and water uptake⁸⁸. Increased stomatal conductance from serotonin application boosted CO₂ fixation, reducing excess energy and photoinhibition, thereby raising the Fv/Fm ratio. The current results were in line with the findings of He et al⁸⁹.. Research on rice has demonstrated that serotonin application can enhance stomatal conductance, spikelet fertility, and ultimately yield under conditions of mild drought stress⁹⁰. Furthermore, serotonin promotes lateral root formation in a dose-dependent fashion by activating the growth of pre-existing lateral root primordia⁹¹. As a result, water absorption by the root increases and stomatal resistance decreases.

Salt stress triggers osmotic accumulation (proline, soluble sugars and soluble proteins) in plants, a key strategy for osmotic adjustment⁷ and cellular protection¹¹. Our findings in bitter melon align with Janah et al⁹². for increased levels under salt stress. Ferchichi et al⁹³. reported that proline is implicated in gene expression, redox homeostasis, and membrane and protein stability. Its accumulation under salinity stress might be due to ABA-induced stomatal closure⁹⁴ and enzymes activity (NADH-dependent glutamate dehydrogenase and pyrroline-5-carboxylate synthetase), suggesting an ABA-independent synthesis of proline⁷⁴. By promoting the buildup of osmolytes like proline and soluble sugars, allantoin helps plants in preserving osmotic balance and turgor pressure, increasing their resilience to dehydration and osmotic stress²⁶. External application of allantoin under salt stress conditions increased the proline content of bitter melon leaves, consistent with the results of Irani and Todd²⁴. Exogenous application of allantoin increased the mRNA levels of the proline biosynthesis enzyme, P5CS (pyrroline-5-carboxylate synthase), in wild-type Arabidopsis under abiotic stress conditions^26,27. In this study, exogenous application of serotonin also increased the content of proline, total soluble sugars and proteins under salinity, consistent with the results of Liu et al⁵. in Rapeseed (Brassica napus L.) seedlings. Serotonin increased soluble protein contents under salt stress condition possibly because serotonin acts as a reactive oxygen species (ROS) scavenger to reduce excess intracellular ROS and repair protein damage under the stress due to structural similarities to melatonin and potential related roles.

To protect against oxidant damage, plants utilize enzymatic and non-enzymatic antioxidants to remove ROS⁹⁵. Key non-enzymatic compounds include phenolic compounds, flavonoids, ascorbate, glutathione, carotenoids, and α-tocopherols⁹⁶. Under salinity stress, oxidative stress emerges as a secondary effect, where accumulated ROS cause oxidative damage to proteins and lipids, leading to cell death⁶³. Under salinity, increase in phenolic compounds observed in some plants including sweet basil⁹⁷. Anthocyanins and flavonoids play a protective role for the photosynthetic system by absorbing surplus light energy, thereby mitigating photoinhibition under environmental stresses. Furthermore, phenolic substances aid in preserving the structure and function of cellular membranes when plants face adverse conditions. As a result, these metabolites are crucial for safeguarding plant tissues against injury from salinity⁶⁴. In bitter melon, salt stress leads to a reduction in ascorbic acid content. This occurs due to an overproduction of ROS that overwhelms the plant’s detoxification capabilities, causing ascorbate to be depleted faster than it can be regenerated⁹⁸.

The phytohormone ABA, synthesized from isoprenoid precursors, is a key regulator of numerous plant functions. It controls stomatal aperture, modulates gene expression, and facilitates adaptation to abiotic challenges like drought, salinity, and low temperatures. ABA also serves as an essential signaling molecule that coordinates a plant’s physiological adjustments to diverse environmental constraints⁹⁹. Salinity stress in tomato increased ABA concentration that then accompanied by stomatal closure of¹⁰⁰, in line with our findings. In our experiment, secondary metabolites and non-enzymatic antioxidants such as ascorbic acid, anthocyanins and flavonoids were higher in allantoin and serotonin treated bitter melon plants under salt stress conditions²⁶. Ascorbic acid is a potent ROS scavenger¹⁰¹, and the stimulation of ascorbic acid by allantoin under salinity conditions (100 mM NaCl) may be due to the effect of allantoin on increasing the levels of antioxidant compounds under salt stress conditions. The allantoin-induced increase in anthocyanin may be due to a stronger antioxidant defense system and exogenous allantoin increases ABA content in Arabidopsis plant, thereby enhancing stress tolerance in plants^26,27. Since ABA enhances anthocyanin biosynthesis¹⁰², there is a high possibility that ABA produced by allantoin stimulates anthocyanin biosynthesis in bitter melon leaf.

This study demonstrated that bitter melon plants exposed to high salinity exhibited significantly greater activity of POD, SOD, APX, and CAT compared to unstressed controls, a finding consistent with reports in other species such as red beet¹⁰³. This can be considered as a sign of the increased ROS generation and a common protective mechanism to mitigate oxidative damage induced by salinity⁷. Plants use antioxidant systems to eliminate ROS. In line with our results, other studies have shown that the application of allantoin and serotonin enhanced antioxidants levels in plants^73,104 probably be triggered by increased ROS production or as a protective mechanism adopted by bitter melon plants against oxidative damage. Ureides, which are nitrogen-rich intermediates generated from purine catabolism, represent a class of metabolites that help shield plants from oxidative injury caused by various stresses. These compounds play vital roles in growth, development, and nitrogen recycling. Evidence suggests ureides function as antioxidants, aiding in ROS detoxification, particularly during early growth stages²⁶. The findings of the current investigation align with prior research demonstrating that externally applied allantoin boosts salt stress tolerance in Arabidopsis seedlings by reinforcing the plant’s antioxidant defense mechanisms⁶⁸. Serotonin exhibits significant antioxidant properties, directly neutralizing ROS and influencing the phenylpropanoid pathway. This interaction involves the regulation of polyphenol oxidase (PPO) and leads to the synthesis of phenolic conjugates such as feruloylserotonin and 4-coumaroylserotonin, thereby enhancing the plant’s antioxidative capacity⁷⁵. It also serves as a precursor for the biosynthesis of various phenolic and amide-based protective compounds⁷³. Furthermore, serotonin functions as a growth regulator with cytokinin-like activity, participating in processes like cell division. Its combined antioxidative and growth-promoting actions contribute to an overall anti-stress effect, which aligns with the findings of the present study⁷³. The interplay between serotonin and phenylpropanoid metabolism, along with its inherent antioxidant power, also supports the stability of key plant pigments, including chlorophyll and anthocyanins¹⁰⁵. The combined use of allantoin and serotonin has not been studied so far, but according to the results of this study their combined application increased the antioxidant compounds of bitter melon under salt stress conditions that play an important role in plant tolerance to salt stress.

A correlative pattern was observed between MDA levels and the activities of SOD, POD, and CAT in the leaves of salt-stressed bitter melon (Fig. 2a). Exposure to 100 mM NaCl resulted in substantial elevations in reactive oxygen species (H₂O₂) and MDA content, indicating severe oxidative damage (Fig. 2b). This oxidative burst was effectively mitigated by the application of allantoin and serotonin, both individually and in combination, which significantly lowered the accumulation of H₂O₂ and MDA. This aligns with established literature on allantoin, which has been shown to preserve membrane integrity in Arabidopsis under salinity by reducing MDA, a key indicator of lipid peroxidation²⁴. This membrane-stabilizing effect, coupled with a decrease in H₂O₂, helps maintain cellular compartmentalization and reduces electrolyte leakage¹⁰⁶. A parallel effect is documented for serotonin, which alleviates salt stress by diminishing MDA content and suppressing membrane lipid peroxidation⁷⁰. Supporting this, Liu et al⁵. reported that exogenous serotonin application reduced MDA and H₂O₂ levels while concurrently restoring chlorophyll content in rapeseed under salt stress. Collectively, these previous findings are in direct concordance with the current results, highlighting the potent, synergistic capacity of allantoin and serotonin to bolster the antioxidant system, scavenge reactive oxygen species, and protect cellular membranes from oxidative degradation.

Our findings indicate a significant decline in K⁺ content under saline conditions. This reduction is likely due to the displacement of vital cations like K⁺ and calcium (Ca²⁺) by the high Na⁺ concentrations typical of saline environments. Potassium is fundamental to plant physiology, acting as a major osmoticum that maintains turgor pressure, a cofactor for enzyme activation in metabolism and synthesis, and a key regulator of stomatal aperture¹⁰⁷. Its role extends to enhancing overall stress resilience by supporting nutrient transport, optimizing photosynthetic gas exchange, and mitigating the adverse impacts of abiotic stressors⁷⁷. The observed reduction in N uptake in salt-stressed cotton plants¹⁰⁸ aligns with the nutrient deficiencies noted in our study. Consistent with these mechanisms, our results demonstrate that allantoin and serotonin counteracted the ionic imbalance caused by salinity. Both compounds increased leaf K⁺ and P concentrations while reducing Na⁺ and Cl⁻ accumulation. Furthermore, their combined application significantly enhanced N content in bitter melon leaves, corroborating previously reported findings and proposed explanations. Allantoin appears to counteract these effects through multiple mechanisms. It promotes root development, thereby expanding the surface area available for nutrient acquisition⁷, and may also upregulate genes responsible for nutrient transporter proteins, enhancing the assimilation and distribution of vital elements⁷⁰. Furthermore, its antioxidant capacity mitigates oxidative damage in root tissues, preserving their functional integrity for nutrient uptake¹⁰⁶. Our findings confirm that allantoin application improved osmoregulation and reduced oxidative injury in bitter melon under salinity. The role of allantoin in salt stress response is further supported by its identification as a key metabolic marker in the roots of rice (Oryza sativa L.), where it accumulates in salt-tolerant cultivars¹⁰⁹. It also contributes to ionic homeostasis by modulating the uptake of Na⁺, K⁺, Ca²⁺, and magnesium (Mg²⁺)⁷¹. Finally, functioning as a nitrogen source, allantoin directly increased the nitrogen content in the leaves of bitter melon subjected to salt stress^110,111. Serotonin modulates the transport of specific ions across biological membranes in plants¹¹². NR plays a key role in NO₃⁻ assimilation that catalyzes the conversion of nitrate to nitrite. The application of serotonin maximized NR activity while increasing salinity concentration hindered its activity due to the reduced uptake of nitrate under salt stress¹².

As a major secondary metabolite, secondary metabolites production is significantly affected by salt stress, which can alter its yield and composition to improve antioxidant capacity. Under favorable conditions, however, most energy is channeled into primary, not secondary, metabolism¹¹³. Increase in secondary metabolites at low levels of salinity stress was also found in bitter melon¹¹, Alcea rosea¹¹⁴ and cucumber⁶⁴. In Lamiaceae family, the quantitative and qualitative composition of the dew secondary metabolites was reduced by salinity¹¹⁵. Allantoin serves as a plant-accessible nitrogen (N) source. Since nitrogen is a critical factor affecting secondary metabolites biosynthesis, as demonstrated in E. purpurea¹¹⁶, allantoin’s role is significant. The importance of N extends to its fundamental role in building organic compounds like enzymes, proteins, and amino acids, which are essential for the formation of secondary metabolites¹¹⁷.

Exposure to environmental stressors often leads to an increase in plant alkaloid concentrations¹¹⁸. Similarly, saponins another class of secondary metabolites accumulate in reaction to biotic and abiotic challenges. For instance, Yang et al¹¹⁹. demonstrated that saponin application improved quinoa seed germination under salinity, likely due to its ROS-scavenging properties. Given that allantoin is a nitrogen-rich intermediate of purine catabolism and a key molecule in nitrogen transport¹²⁰, it could directly contribute to the synthesis of nitrogen-containing alkaloids in bitter melon fruit. In a parallel manner, serotonin—a tryptophan-derived compound—is part of a broader metabolic network involved in stress adaptation. Tryptophan serves as a precursor for a wide array of stress-responsive molecules, including auxins, alkaloids, and phytoalexins¹²¹. Therefore, the application of serotonin provides a plausible explanation for the observed increase in alkaloid content in bitter melon, linking it to the mobilization of key biosynthetic pathways under stress.

Salinity stress is known to alter fruit carbohydrate levels, though the effect is species-specific and dependent on stress intensity¹²². While data on bitter melon is limited, research on tomato has shown that salt stress can enhance fruit quality by elevating dry matter, soluble solids, amino acids, and concentrations of sugars like glucose, fructose, and sucrose¹²³. This accumulation is partly governed by the transcriptional regulation of invertases, key enzymes that modulate sugar metabolism in response to environmental challenges¹²², indicating that stress-induced changes in gene expression for these enzymes can direct sugar partitioning to the fruit. Research in wheat has demonstrated that allantoin application promotes the accumulation of osmolytes such as amino acids, soluble proteins, sugars, and proline, which contribute to osmotic adjustment and ROS scavenging¹⁰⁶. In a complementary finding, exogenous melatonin was shown to enhance plum fruit quality by modulating metabolic pathways to increase soluble sugar content and reduce organic acids¹²⁴. Given the structural and functional similarities between melatonin and serotonin, it is plausible that serotonin exerts a comparable positive influence on fruit quality. In the present study, the application of allantoin and serotonin, especially in combination, led to a significant increase in secondary Essential in bitter melon fruit under salt stress. This enhancement can be reasonably attributed to the mechanisms outlined in the aforementioned studies, collectively indicating a beneficial role in improving the qualitative attributes of bitter melon.

The concentration of phenolic acids in both the leaf and fruit of bitter melon was elevated in response to salinity and biostimulant treatments. These compounds perform diverse biological roles, including defense against ultraviolet radiation, pathogens, and the reactive oxygen species generated by environmental stresses like salinity¹¹⁴. This response is not unique to bitter melon; for instance, salt stress has been shown to enhance levels of caffeic, ferulic, and chlorogenic acids in pepper⁷³. In our study, the rise in cinnamic acid and other phenolic acids was closely associated with improved growth and physiological performance under salt stress. The significant accumulation of p-coumaric acid likely helped mitigate oxidative pressure due to its potent hydroxyl group-mediated radical scavenging capacity. The presence of ferulic acid under osmotic stress may contribute to the fortification of the plant cell wall, potentially restricting excessive cell elongation¹²⁵. Furthermore, ferulic acid is implicated in salt tolerance mechanisms by reducing lipid peroxidation through the activation of antioxidant enzymes and by promoting the accumulation of proline and soluble sugars in bitter melon leaves.

N availability is a key factor regulating the biosynthesis of phenolic compounds. For instance, nitrogen fertilization has been shown to elevate concentrations of phenolic acids like ferulic acid and vanillic acid¹²⁶. As allantoin can serve as a nitrogen source for plants, its application provides a plausible explanation for the observed increase in phenolic acids in bitter melon. A parallel mechanism exists for compounds like melatonin; in salt-stressed barley, melatonin application upregulated key phenylpropanoid pathway genes and enzymes (phenylalanine ammonia-lyase and cinnamate 4-hydroxylase), leading to a significant accumulation of phenolic acids such as ferulic acid and p-coumaric acid. Similarly, Sheikhalipour et al³. reported that melatonin treatment enhanced phenolic acid content in bitter melon under salinity. In the current investigation, the combined foliar application of allantoin and serotonin significantly boosted phenolic acid levels in both the leaves and fruits of salt-stressed bitter melon, a finding that aligns with the mechanisms and results described in these previous studies.

Conclusion

To mitigate the detrimental effects of salt stress, plants initiate a suite of intricate physiological and defensive adaptations. Allantoin has emerged as a significant compound in enhancing salinity tolerance and improving agricultural productivity. Its function as a nitrogen source, coupled with its role in stress resilience, positions it as a promising agent for boosting crop yields and supporting global food security. Exogenous serotonin has antioxidation properties, regulates osmotic activity and promotes growth, which then could effectively improve salt tolerance of plants. In the present study, allantoin and serotonin have been found to be an essential player in plant processes particularly mitigating salt stress in bitter melon as they played a role in antioxidant properties, ion homeostasis and water balance. Allantoin and serotonin exhibited the capacity to improve chlorophyll content and nutrient uptake in leaves, particularly in essential elements like P, N, and K⁺, crucial for bitter melon growth. Furthermore, the combined application of allantoin and serotonin showed a pronounced capacity to modulate the plant’s antioxidant defense system. To confirm these promising results, subsequent research should focus on field-scale trials to verify the treatment’s effectiveness in enhancing the growth of bitter melon and other economically significant crops under saline conditions. The simultaneous application of allantoin and serotonin improved the studied traits in bitter melon, which could be due to potential interference between abscisic acid (ABA) signaling (activated by allantoin) and auxin/cytokinin pathways (influenced by serotonin) or the joint effects of both compounds on ROS inhibition. The application of allantoin and serotonin in bitter melon was associated with an increase in the quantitative and qualitative characteristics of the fruit.

Supplementary Information

Below is the link to the electronic supplementary material.

Supplementary Material 1^{(1.7MB, docx)}

Acknowledgements

The authors of the article are grateful to Razi University and Agricultural University of Athens.

Author contributions

M.A. supervised the experiments, wrote and critically revised the manuscript. G.G. Project design. S.J.H. performed the experiments. S.P and G.N. contributed to project administration, investigation and revision of the manuscript. All authors have read and agreed to the published version of the manuscript.

Data availability

All data are available in the manuscript file.

Declarations

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

1.Tabassum, M. et al. Chitosan modulated antioxidant activity, inorganic ions homeostasis and endogenous melatonin to improve yield of Pisum sativum L. accessions under salt stress. Sci. Hortic.323, 112509. 10.1016/j.scienta.2023.112509 (2024). [Google Scholar]
2.Chang, B., Yang, L., Cong, W., Zu, Y. & Tang, Z. The improved resistance to high salinity induced by trehalose is associated with ionic regulation and osmotic adjustment in Catharanthus roseus. Plant Physiol. Biochem.77, 140–148. 10.1016/j.plaphy.2014.02.001 (2014). [DOI] [PubMed] [Google Scholar]
3.Sheikhalipour, M. et al. Effect of melatonin foliar sprays on morphophysiological attributes, fruit yield and quality of Momordica charantia L. under salinity stress. Plant. Physiol. Biochem.205, 108194. 10.1016/j.plaphy.2023.108194 (2023a). [DOI] [PubMed] [Google Scholar]
4.Pal, S. C. et al. Combined use of seaweed extract and arbuscular mycorrhizal fungi for alleviating salt stress in bell pepper (Capsicum annuum L.). Sci. Hortic.325, 112597. 10.1016/j.scienta.2023.112597 (2024). [Google Scholar]
5.Liu, Y. et al. Exogenous serotonin improves salt tolerance in rapeseed (Brassica napus L.) seedlings. Agronomy11(2), 1–11. 10.3390/agronomy11020400 (2021). [Google Scholar]
6.Zulfiqar, F. et al. Melatonin seed priming improves growth and physio-biochemical aspects of Zinnia elegans under salt stress. Sci. Hortic.323, 112495. 10.1016/j.scienta.2023.112495 (2024). [Google Scholar]
7.Gohari, G. et al. Characterization of Octa-aminopropyl polyhedral oligomeric silsesquioxanes (OA-POSS) nanoparticles and their effect on sweet basil (Ocimum basilicum L.) response to salinity stress. Plant Physiol. Biochem.196, 89–102. 10.1016/j.plaphy.2023.01.019 (2023). [DOI] [PubMed] [Google Scholar]
8.Alisofi, S., Einali, A. & Sangtarash, M. H. Jasmonic acid-induced metabolic responses in bitter melon (Momordica charantia) seedlings under salt stress. J. Hortic. Sci. Biotechnol.95(2), 247–259. 10.1080/14620316.2019.1663135 (2020). [Google Scholar]
9.Sheikhalipour, M. et al. Exogenous melatonin increases salt tolerance in bitter melon by regulating ionic balance, antioxidant system and secondary metabolism-related genes. BMC Plant Biol.22(1), 1–17. 10.1186/s12870-022-03728-0 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]
10.Sheikhalipour, M. et al. Seedling nanopriming with selenium-chitosan nanoparticles mitigates the adverse effects of salt stress by inducing multiple defence pathways in bitter melon plants. Int. J. Biol. Macromol.242 (3), 124923. 10.1016/j.ijbiomac.2023.124923 (2023b). [DOI] [PubMed] [Google Scholar]
11.Sheikhalipour, M. et al. Chitosan–selenium nanoparticle (Cs–Se NP) foliar spray alleviates salt stress in bitter melon. Nanomaterials11(3), 1–22. 10.3390/nano11030684 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]
12.Zahra, N. et al. Serotonin improves plant growth, foliar functions and antioxidant defence system in Ethiopian mustard (Brassica carinata A. Br). S AFR. J. BOT.170 (2), 1–9. 10.1016/j.sajb.2024.05.002 (2024). [Google Scholar]
13.Kaur, H., Chowrasia, S., Gaur, V. S. & Mondal, T. K. Allantoin: Emerging role in plant abiotic stress tolerance. Plant Mol. Biol. Rep.39(1), 648–661. 10.1007/s11105-021-01280-z (2021). [Google Scholar]
14.Abbas, M. et al. Biochemical stress markers, antioxidants, and infectious wound-healing potential of UV irradiation and salt stress effects on the pre-treated seed of bitter melon (Momordica charantia L.). Dose. Response.19(4), 1–11. 10.1177/15593258211044062 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]
15.Singla, D., Sangha, M. K., Singh, M., Pathak, M. & Bala, M. Variation of mineral composition in different fruit parts of bitter gourd (Momordica charantia L.). Biol. Trace Elem. Res.201(10), 4961–4971. 10.1007/s12011-022-03546-3 (2023). [DOI] [PubMed] [Google Scholar]
16.Alomrani, S. O. et al. Effect of sodium hydrosulfide on physicochemical characteristics and melatonin mediated stress mitigation in bitter gourd (Momordica charantia L.) grown under lead stress. Sci. Hortic.323, 112547. 10.1016/j.scienta.2023.112547 (2024). [Google Scholar]
17.Chaudhury, P. Role of secondary metabolites of Momordica charantia in combating copper induced stress. AJABTR4(1), 5–29. 10.15864/ajabtr.412 (2023). [Google Scholar]
18.Ying, S. et al. Allantoin alleviates seed germination the rmoinhibition in Arabidopsis. Phyton91(9), 1893–1904. 10.32604/phyton.2022.022679 (2022). [Google Scholar]
19.Becker, L. C. et al. Final report of the safety assessment of allantoin and its related complexes. Int. J. Toxicol.29(3), 84–97. 10.1177/1091581810362805 (2010). [DOI] [PubMed] [Google Scholar]
20.Zhang, Y. M., Chu, Z. D., Feng, X., Sun, Y. X. & Gong, Y. H. Roles of allantoin in plant defense responses. Zhiwu Shengli Xuebao/Plant Physiol. J.53 (7), 1131–1138. 10.13592/j.cnki.ppj.2016.0512 (2017). [Google Scholar]
21.Fahad, S. et al. Suppressing photorespiration for the improvement in photosynthesis and crop yields: A review on the role of S-allantoin as a nitrogen source. J. Environ. Manag. 237, 644–651. 10.1016/j.jenvman.2019.02.082 (2019). [DOI] [PubMed] [Google Scholar]
22.Raihan, M. R. H., Rahman, M., Rastogi, A., Fujita, M. & Hasanuzzaman, M. Exogenous allantoin confers rapeseed (Brassica campestris) tolerance to simulated drought by improving antioxidant metabolism and physiology. Antioxidants12(8), 1–23. 10.3390/antiox12081508 (2023). [DOI] [PMC free article] [PubMed] [Google Scholar]
23.Liu, L. et al. Exogenous allantoin improves the salt tolerance of sugar beet by increasing putrescine metabolism and antioxidant activities. Plant Physiol. Biochem.154, 699–713. 10.1016/j.plaphy.2020.06.034 (2020). [DOI] [PubMed] [Google Scholar]
24.Irani, S., Lobo, J. M., Gray, G. R. & Todd, C. D. Allantoin accumulation in response to increased growth irradiance in Arabidopsis thaliana. Biol. Plant.62(1), 181–187. 10.1007/s10535-017-0747-2 (2018). [Google Scholar]
25.Dresler, S. et al. Allantoin attenuates cadmium-induced toxicity in cucumber plants. Ecotoxicol. Environ. Saf.170, 120–126. 10.1016/j.ecoenv.2018.11.119 (2019). [DOI] [PubMed] [Google Scholar]
26.Kaur, R., Chandra, J., Varghese, B. & Keshavkant, S. Allantoin: A potential compound for the mitigation of adverse effects of abiotic stresses in plants. Plants12(17), 1–21. 10.3390/plants12173059 (2023). [DOI] [PMC free article] [PubMed] [Google Scholar]
27.Watanabe, S. et al. The purine metabolite allantoin enhances abiotic stress tolerance through synergistic activation of abscisic acid metabolism. Plant Cell Environ.37(4), 1022–1036. 10.1111/pce.12218 (2014a). [DOI] [PubMed] [Google Scholar]
28.Lu, S. et al. Combined metabolomic and transcriptomic analysis reveals allantoin enhances drought tolerance in rice. Int. J. Mol. Sci.23(22), 1–20. 10.3390/ijms232214172 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]
29.Erland, L. A., Turi, C. E. & Saxena, P. K. Serotonin in plants: origin, functions, and implications. Serotonin10.1016/B978-0-12-800050-2.00002-4 (2019). [Google Scholar]
30.Zahra, N. et al. Regulation of photosynthesis under salt stress and associated tolerance mechanisms. Plant Physiol. Biochem.178, 55–69. 10.1016/j.plaphy.2022.03.003 (2022). [DOI] [PubMed] [Google Scholar]
31.Ahmad, I. et al. Integrated approaches for increasing plant yield under salt stress. Front. Plant Sci.14, 1–11. 10.3389/fpls.2023.1215343 (2023). [DOI] [PMC free article] [PubMed] [Google Scholar]
32.Pontes, C. V. S. et al. Exogenous serotonin and 24-Epibrassinolide boost root protection and suppress oxidative damages occasioned by severe water deficit in soybean seedlings. J. Plant Growth Regul.43(6), 1–11. 10.1007/s00344-023-11220-8 (2024). [Google Scholar]
33.Wan, J. et al. Comparative physiological responses and transcriptome analysis reveal the roles of melatonin and serotonin in regulating growth and metabolism in Arabidopsis. BMC Plant Biol.18(1), 1–14. 10.1186/s12870-018-1548-2 (2018). [DOI] [PMC free article] [PubMed] [Google Scholar]
34.Mukherjee, S., David, A., Yadav, S., Baluška, F. & Bhatla, S. C. Salt stress-induced seedling growth inhibition coincides with differential distribution of serotonin and melatonin in sunflower seedling roots and cotyledons. Physiol. Plant.152 (4), 714–728. 10.1111/ppl.12218 (2014). [DOI] [PubMed] [Google Scholar]
35.Akcay, U. C. & Okudan, N. Exogenous serotonin improves drought and salt tolerance in tomato seedlings. J. Plant Growth Regul.101(1), 239–249. 10.21203/rs.3.rs-2714889/v1 (2023). [Google Scholar]
36.Lichtenthaler, H. K. Chlorophylls and carotenoids: Pigments of photosynthetic biomembranes. Methods Enzymol.148, 350–382. 10.1016/0076-6879(87)48036-1 (1987). [Google Scholar]
37.Semer, J., Navrátil, M., Špunda, V. & Štroch, M. Chlorophyll fluorescence parameters to assess utilization of excitation energy in photosystem II independently of changes in leaf absorption. J. Photochem. Photobiol. B, Biol.197, 111535. 10.1016/j.jphotobiol.2019.111535 (2019). [DOI] [PubMed] [Google Scholar]
38.Schonfeld, M. A., Johnson, R. C., Carver, B. F. & Mornhinweg, D. W. Water relations in winter wheat as drought resistance indicators. Crop Sci.28(3), 526–531. 10.2135/cropsci1988.0011183X002800030021x (1988). [Google Scholar]
39.Ben Hamed, K., Castagna, A., Salem, E. A., Ranieri, A. & Abdelly, C. Sea fennel (Crithmum maritimum L.) under salinity conditions: A comparison of leaf and root antioxidant responses. J. Plant Growth Regul.53(3), 185–194. 10.1007/s10725-007-9217-8 (2007). [Google Scholar]
40.Irigoyen, J. J., Einerich, D. W. & Sanchez-Diaz, M. Water stress induced changes in concentrations of proline and total soluble sugars in nodulated alfalfa (Medicago sativa L.) plants. Physiol. Plant.84(1), 55–60. 10.1111/j.1399-3054.1992.tb08764.x (1992). [Google Scholar]
41.Paquin, R. & Lechasseur, P. Observation sur une method de dosage de la proline libre Dans les extrats deplants. Can. J. Bot.57(18), 1851–1854. 10.1139/b79-233 (1979). [Google Scholar]
42.Bor, J. Y., Chen, H. Y. & Yen, G. H. Evaluation of antioxidant activity and inhibitory effect on nitric oxide production of some common vegetables. J. Agric. Food Chem.54, 1680–1686 (2006). [DOI] [PubMed] [Google Scholar]
43.Masukasu, H., Karin, O. & Kyoto, H. Enhancement of anthocyanin biosynthesis by sugar in radish (Raphanus sativus) hypocotyl. Plant Sci.164, 259–265. 10.1016/S0168-9452(02)00408-9 (2003). [Google Scholar]
44.Sharma, T., Gamit, R., Acharya, R. & Shukla, V. J. Quantitative estimation of total tannin, alkaloid, phenolic, and flavonoid content of the root, leaf, and whole plant of Byttneria herbacea Roxb.. AYU (An International Quarterly Journal of Research in Ayurveda)42(3), 143–147. 10.4103/ayu.AYU_25_19 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]
45.Singleton, V. L. & Rossi, J. A. Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents. Am. J. Enol. Vitic.16(3), 144–153. 10.5344/ajev.1965.16.3.144 (1965). [Google Scholar]
46.Sini, K. R., Sinha, B. N. & Karpagavalli, M. Determining the antioxidant activity of certain medicinal plants of Attapady, (Palakkad), India using DPPH assay. Curr. Bot.1(1), 13–16 (2010). [Google Scholar]
47.Chen, S. et al. Arbuscular mycorrhizal fungi (AMF) increase growth and secondary metabolism in cucumber subjected to low temperature stress. Sci. Hortic.160, 222–229. 10.1016/j.scienta.2013.05.039 (2013). [Google Scholar]
48.Li, Z., Zhao, X., Sandhu, A. K. & Gu, L. Effects of exogenous abscisic acid on yield, antioxidant capacities, and phytochemical contents of greenhouse grown lettuces. J. Agric. Food Chem.58 (10), 6503–6509. 10.1021/jf1006962 (2010). [DOI] [PubMed] [Google Scholar]
49.Singh, R., Kumar, A., Giri, D. D., Bhuvaneshwari, K. & Pandey, K. D. Gas chromatography-mass spectrometry analysis and phytochemical screening of methanolic fruit extract of Momordica charantia. J. Recent Adv. Agric.1(4), 122–127 (2012). [Google Scholar]
50.Velikova, V. & Loreto, F. On the relationship between isoprene emission and thermotolerance in Phragmites australis leaves exposed to high temperatures and during the recovery from a heat stress. Plant Cell Environ.28(3), 318–327. 10.1111/j.1365-3040.2004.01314.x (2005). [Google Scholar]
51.Heath, R. L. & Packer, L. Photo-peroxidation in isolated chloroplasts: I. Kinetics and stoichiometry of fatty acid peroxidation. Arch. Biochem. Biophys.125(1), 189–198. 10.1016/0003-9861(68)90654-1 (1968). [DOI] [PubMed] [Google Scholar]
52.Bradford, M. M. Rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem.72(1–2), 248–254. 10.1016/0003-2697(76)90527-3 (1976). [DOI] [PubMed] [Google Scholar]
53.Bergmeyer, H. U. Methods of enzymatic analysis 636–647 (Akademie Verlag, 1970). [Google Scholar]
54.Nakano, Y. & Asada, K. Hydrogen peroxide is scavenged by ascorbate-specific peroxidase in spinach chloroplasts. Plant Cell Physiol.22(5), 867–880. 10.1093/oxfordjournals.pcp.a076232 (1981). [Google Scholar]
55.Herzog, V. & Fahimi, H. D. A new sensitive colorimetric assay for peroxidase using 3,3’-diaminobenzidine as hydrogen donor. Anal. Biochem.55(2), 554–562. 10.1016/0003-2697(73)90144-9 (1973). [DOI] [PubMed] [Google Scholar]
56.Dhindsa, R. S., Plumb-Dhindsa, P. A. M. E. L. A. & Thorpe, T. A. Leaf senescence: Correlated with increased levels of membrane permeability and lipid peroxidation, and decreased levels of superoxide dismutase and catalase. J. Exp. Bot.32(1), 93–101. 10.1093/jxb/32.1.93 (1981). [Google Scholar]
57.Munns, R., Wallace, P. A., Teakle, N. L. & Colmer, T. D. Measuring soluble ion concentrations (Na, K, Cl) in salt-treated plants. In Plant Stress Tolerance, Methods in Molecular Biology Vol. 386 (ed. Sunkar, R.) 371–382 (Humana, 2010). [DOI] [PubMed] [Google Scholar]
58.Adesanwo, O. O., Ige, D. V., Thibault, L., Flaten, D. & Akinremi, W. Comparison of colorimetric and ICP methods of phosphorus determination in soil extracts. Commun. Soil Sci. Plant Anal.44(21), 3061–3075. 10.1080/00103624.2013.832771 (2013). [Google Scholar]
59.Gupta, P. k. Soil, plant, water and fertilizer analysis (2nd Ed.). Published by Agrobios (INDIA).147. (1999).
60.Zhou, H. et al. Insights into plant salt stress signaling and tolerance. J. Genet. Genomics51(1), 16–34. 10.1016/j.jgg.2023.08.007 (2024). [DOI] [PubMed] [Google Scholar]
61.Abdelkefi, N. et al. Enhanced salt stress tolerance in tomato plants following inoculation with newly isolated plant growth-promoting rhizobacteria. Sci. Hortic.328, 112921. 10.1016/j.scienta.2024.112921 (2024). [Google Scholar]
62.Shalaby, O. A. Moringa leaf extract increases tolerance to salt stress, promotes growth, increases yield, and reduces nitrate concentration in lettuce plants. Sci. Hortic.325, 112654. 10.1016/j.scienta.2023.112654 (2024). [Google Scholar]
63.Amerian, M., KhoramiVafa, M., Palangi, A., Gohari, G. & Ntatsi, G. The effect of different levels of urea and sodium selenate on the morphophysiological characteristics of garlic (Allium sativum L). Sci. Hortic.337, 1–14. 10.1016/j.scienta.2024.113469 (2024a). [Google Scholar]
64.Amerian, M., Palangi, A., Gohari, G. & Ntatsi, G. Humic acid and grafting as sustainable agronomic practices for increased growth and secondary metabolism in cucumber subjected to salt stress. Sci. Rep.14 (1), 1–18. 10.1038/s41598-024-66677-8 (2024b). [DOI] [PMC free article] [PubMed] [Google Scholar]
65.Gohari, G. et al. Titanium dioxide nanoparticles (TiO₂ NPs) promote growth and ameliorate salinity stress effects on essential oil profile and biochemical attributes of Dracocephalum moldavica. Sci. Rep.10 (1), 1–14. 10.1038/s41598-020-57794-1 (2020b). [DOI] [PMC free article] [PubMed] [Google Scholar]
66.Kanwal, R. et al. Exogenous ascorbic acid as a potent regulator of antioxidants, osmo-protectants, and lipid peroxidation in pea under salt stress. BMC Plant. Biol.24 (1), 1–16. 10.1186/s12870-024-04947-3 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]
67.Mohammadi, H. et al. Interaction of NaCl salinity and light intensity affect growth, physiological traits and essential oil constituents in Artemisia dracunculus L. (tarragon). Biochem. Syst. Ecol.107, 1–9. 10.1016/j.bse.2023.104626 (2023). [Google Scholar]
68.Irani, S. & Todd, C. D. Exogenous allantoin increases Arabidopsis seedlings tolerance to NaCl stress and regulates expression of oxidative stress response genes. J. Plant. Physiol.221, 43–50. 10.1016/j.jplph.2017.11.011 (2018). [DOI] [PubMed] [Google Scholar]
69.Wang, H. et al. Effects of salt stress on ion balance and nitrogen metabolism of old and young leaves in rice (Oryza sativa L). BMC Plant. Biol.12 (1), 1–11 (2012). http://www.biomedcentral.com/1471-2229/12/194 [DOI] [PMC free article] [PubMed] [Google Scholar]
70.Dawood, M. F., Tahjib-Ul-Arif, M., Sohag, A. A. M., Abdel Latef, A. A. H. & Ragaey, M. M. Mechanistic insight of allantoin in protecting tomato plants against ultraviolet C stress. Plants10(1), 1–23. 10.3390/plants10010011 (2020). [DOI] [PMC free article] [PubMed] [Google Scholar]
71.Chowrasia, S. et al. Allantoin improves salinity tolerance in Arabidopsis and rice through synergid activation of abscisic acid and brassinosteroid biosynthesis. Plant Mol. Biol.112(3), 143–160. 10.1007/s11103-023-01350-8 (2023). [DOI] [PubMed] [Google Scholar]
72.Casartelli, A. et al. Opposite fates of the purine metabolite allantoin under water and nitrogen limitations in bread wheat. Plant Mol. Biol.99(4–5), 477–497. 10.1007/s11103-019-00831-z (2019). [DOI] [PubMed] [Google Scholar]
73.Arya, M., Kumar, G. & Giridhar, P. Serotonin-salt-stress model-induced cell growth via promoting an antioxidant system and secondary metabolites in Capsicum annuum cell suspension culture. ACS Omega10.1021/acsomega.4c05353 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]
74.Kaur, H., Mukherjee, S., Baluska, F. & Bhatla, S. C. Regulatory roles of serotonin and melatonin in abiotic stress tolerance in plants. Plant Signal. Behav.10(11), 1–8. 10.1080/15592324.2015.1049788 (2015). [DOI] [PMC free article] [PubMed] [Google Scholar]
75.Roychoudhury, A. Multifaceted roles of serotonin in plants. Young Scientist- Tomorrow’s Science Begins Today5(1), 26–35 (2021). [Google Scholar]
76.Erland, L. A. E. & Saxena, P. K. Beyond a neurotransmitter: The role of serotonin in plants. Neurotransmitter4(5), 1–12 (2017). [Google Scholar]
77.Danish, S. et al. The role of strigolactone in alleviating salinity stress in chili pepper. BMC Plant Biol.24(1), 1–13. 10.1186/s12870-024-04900-4 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]
78.Wu, Y. et al. 5-Aminolevulinic acid (ALA) alleviated salinity stress in cucumber seedlings by enhancing chlorophyll synthesis pathway. Front. Plant. Sci.9, 11–16. 10.3389/fpls.2018.00635 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]
79.Stefanov, M. A., Rashkov, G. D., Borisova, P. B. & Apostolova, E. L. Changes in Photosystem II complex and physiological activities in pea and maize plants in response to salt stress. Plants13(7), 1–17. 10.3390/plants13071025 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]
80.Shah, I. H. et al. Exploring the role of nitrogen and potassium in photosynthesis implications for sugar: Accumulation and translocation in horticultural crops. Sci. Hortic.327, 112832. 10.1016/j.scienta.2023.112832 (2024). [Google Scholar]
81.Liang, D. et al. Exogenous melatonin promotes biomass accumulation and photosynthesis of kiwifruit seedlings under drought stress. Sci. Hortic.246, 34–43. 10.1016/j.scienta.2018.10.058 (2019). [Google Scholar]
82.Imran, M. et al. Exogenous melatonin induces drought stress tolerance by promoting plant growth and antioxidant defence system of soybean plants. AoB Plants13(4), 1–12. 10.1093/aobpla/plab026 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]
83.Yu, Y. et al. The role of phyto-melatonin and related metabolites in response to stress. Molecules23(8), 1–15. 10.3390/molecules23081887 (2018). [DOI] [PMC free article] [PubMed] [Google Scholar]
84.Shiade, S. R. G. et al. Plant metabolites and signaling pathways in response to biotic and abiotic stresses: Exploring bio stimulant applications. Plant Stress12, 1–12. 10.1016/j.stress.2024.100454 (2024). [Google Scholar]
85.Abbas, A. et al. NaCl stress, tissue specific Na⁺ and K⁺ up-take and their effect on growth and physiology of Helianthus annuus L. and Solanum lycopersicum L. Sci. Hortic.326, 1–11. 10.1016/j.scienta.2023.112454 (2024). [Google Scholar]
86.Liao, Q. et al. Stomatal conductance modulates maize yield through water use and yield components under salinity stress. Agric. Water Manag.294, 108717 (2024). [Google Scholar]
87.Li, J. et al. Heterogeneous saline water irrigation improves stomatal and nonstomatal restrictions to decrease yield reduction threshold in cherry tomato. Sci. Hortic.326, 112788 (2024). [Google Scholar]
88.Zhang, D. et al. Unraveling the impacts of nano-scale carbon exposure on nitrogen metabolism during early seedling establishment in Zea mays L. roots. Plant Soil502(1), 245–265 (2024). [Google Scholar]
89.He, H. et al. Study on the mechanism of exogenous serotonin improving cold tolerance of rapeseed (Brassica napus L.) seedlings. J. Plant Growth Regul.94(2), 161–170. 10.1007/s10725-021-00700-0 (2021). [Google Scholar]
90.Ramakrishna, A., Giridhar, P. & Ravishanker, G. A. Phytoserotonin: A review. Plant Signal. Behav.6(6), 800–809. 10.4161/psb.6.6.15242 (2011). [DOI] [PMC free article] [PubMed] [Google Scholar]
91.Dehghanian, Z. et al. Role of neurotransmitters (biomediators) in plant responses to stress. Plants (Basel)13(22), 1–31. 10.3390/plants13223134 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]
92.Janah, I., Ben-Laouane, R., Elhasnaoui, A., Anli, M. & Meddich, A. The induction of salt stress tolerance by gibberellic acid treatment in Stevia rebaudiana Bertoni plants. Int. J. Plant Biol.15(2), 505–516. 10.3390/ijpb15020038 (2024). [Google Scholar]
93.Ferchichi, S. et al. Hordeum vulgare and Hordeum maritimum respond to extended salinity stress displaying different temporal accumulation pattern of metabolites. Funct. Plant Biol.45(11), 1096–109. (2018). [DOI] [PubMed] [Google Scholar]
94.Fatma, M. et al. Ethylene and sulfur coordinately modulate the antioxidant system and ABA accumulation in mustard plants under salt stress. Plants (Basel)10(1), 1–21. 10.3390/plants10010180 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]
95.Singh, A. & Satheeshkumar, P. K. Reactive Oxygen Species (ROS) and ROS Scavengers in Plant Abiotic Stress Response. In Stress Biology in Photosynthetic Organisms: Molecular Insights and Cellular Responses 41–63 (Springer Nature Singapore, 2024). [Google Scholar]
96.Eke, P. et al. Interaction of Melatonin with Reactive Oxygen Species in Plants. In Melatonin in Plants: A Regulator for Plant Growth and Development 137–171 (Springer Nature Singapore, 2023). [Google Scholar]
97.Gohari, G. et al. Interaction between hydrogen peroxide and sodium nitroprusside following chemical priming of Ocimum basilicum L. against salt stress. Physiol. Plant.168(2), 361–373. 10.1111/ppl.13020 (2020a). [DOI] [PubMed] [Google Scholar]
98.Celi, G. E., Gratão, P. L., Lanza, M. G. & Dos Reis, A. R. Physiological and biochemical roles of ascorbic acid on mitigation of abiotic stresses in plants. Plant Physiol. Biochem.202, 107970. 10.1016/j.plaphy.2023.107970 (2023). [DOI] [PubMed] [Google Scholar]
99.Yan, F. et al. Melatonin alleviates abscisic acid deficiency inhibition on photosynthesis and antioxidant systems in rice under salt stress. Phyton.93(7), 1421–1440. 10.32604/phyton.2024.053914 (2024). [Google Scholar]
100.Liang, K., Chen, Y., Hou, J. & Liu, F. Elevated CO2-conferred sodium homeostasis is linked to abscisic acid-mediated stomatal closure and signalling pathway in tomato plants. Hortic. Plant. J.10.1016/j.hpj.2024.01.005 (2024). [Google Scholar]
101.Singh Gill, S. & Tuteja, N. Cadmium stress tolerance in crop plants. Plant Signal. Behav.6(2), 215–222. 10.4161/psb.6.2.14880 (2011). [DOI] [PMC free article] [PubMed] [Google Scholar]
102.Gu, S., Jacobs, S. & Du, G. Efficacy, rate and timing of applications of abscisic acid to enhance fruit anthocyanin contents in ‘Cabernet Sauvignon’grapes. J. Hortic. Sci. Biotechnol.86(5), 505–510. 10.1080/14620316.2011.11512796 (2011). [Google Scholar]
103.Colak, N. The effect of exogenous N-acetylcysteine on the phenolic profile and antioxidant enzyme activities in two betalainic red beet (Beta vulgaris L.) leaves under salt stress. Acta Physiol. Plant.46(9), 81. 10.1007/s11738-024-03713-0 (2024). [Google Scholar]
104.Wang, J. et al. Transcriptome and metabolome analyses reveal complex molecular mechanisms involved in the salt tolerance of rice induced by exogenous allantoin. Antioxid11(10), 2045 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]
105.Bajwa, V. S. et al. Identification and characterization of serotonin as ananti-browning compound of apple and pear. Postharvest Biol. Technol.110, 183–189. 10.1016/j.postharvbio.2015.08.018 (2015). [Google Scholar]
106.Alam, R., Rasheed, R., Ashraf, M. A., Hussain, I. & Ali, S. Allantoin alleviates chromium phytotoxic effects on wheat by regulating osmolyte accumulation, secondary metabolism, ROS homeostasis and nutrient acquisition. J. Hazard. Mater.458, 131920. 10.1016/j.jhazmat.2023.131920 (2023). [DOI] [PubMed] [Google Scholar]
107.Rahneshan, Z., Nasibi, F. & Moghadam, A. A. Effects of salinity stress on some growth, physiological, biochemical parameters and nutrients in two pistachio (Pistacia vera L.) rootstocks. J. Plant Interact.13(1), 73–82. 10.1080/17429145.2018.1424355 (2018). [Google Scholar]
108.Heng, T. et al. The effects of soil salt stress on the Nitrogen uptake, yield response and Nitrogen use efficiency of cotton in arid areas. Agronomy14(1), 1–12. 10.3390/agronomy14010229 (2024). [Google Scholar]
109.Nam, M. H. et al. Metabolite profiling of diverse rice germplasm and identification of conserved metabolic markers of rice roots in response to long-term mild salinity stress. Int. J. Mol. Sci.16(9), 21959–21974. 10.3390/ijms160921959 (2015). [DOI] [PMC free article] [PubMed] [Google Scholar]
110.Jahan, B., Al Ajmi, M. F., Rehman, M. T. & Khan, N. A. Treatment of nitric oxide supplemented with nitrogen and sulfur regulates photosynthetic performance and stomatal behavior in mustard under salt stress. Physiol. Plant.168(2), 490–510. 10.1111/ppl.13056 (2020). [DOI] [PubMed] [Google Scholar]
111.Jahan, B. et al. Coordinated role of nitric oxide, ethylene, nitrogen, and sulfur in plant salt stress tolerance. Stresses1(3), 181–199. 10.3390/stresses1030014 (2021). [Google Scholar]
112.Erland, L. A. Views and perspectives on the indoleamines serotonin and melatonin in plants: Past, present and future. Plant Signal. Behav.19(1), 2366545 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]
113.Krause, S. T. et al. The biosynthesis of thymol, carvacrol, and thymohydroquinone in Lamiaceae proceeds via cytochrome P450s and a short-chain dehydrogenase. Proc. Natl. Acad. Sci. U. S. A.118(52), 1–10. 10.1073/pnas.2110092118 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]
114.Sadeghi, A., Razmjoo, J., Karimmojeni, H., Baldwin, T. C. & Mastinu, A. Changes in secondary metabolite production in response to salt stress in Alcea rosea L.. Hortic.10(2), 1–26. 10.3390/horticulturae10020139 (2024). [Google Scholar]
115.Stefanakis, M. K. et al. The Effect of Salinity and Drought on the Essential Oil Yield and Quality of Various Plant Species of the Lamiaceae Family (Mentha spicata L., Origanum dictamnus L., Origanum onites L). Hortic10, 1–14. 10.3390/horticulturae10030265 (2024). [Google Scholar]
116.Petkova, N., Ivanova, L., Filova, G., Ivanov, I. & Denev, P. Antioxidants and carbohydrate content in infusions and microwave extracts from eight medicinal plants. J. Appl. Pharm. Sci.7 (10), 055–061. 10.7324/JAPS.2017.71008 (2017). [Google Scholar]
117.Zheng, Y., Dixon, M. & Saxena, P. Greenhouse production of Echinacea purpurea (L.) and E. angustifolia using different growing media, NO₃^–/NH₄⁺ ratios and watering regimes. Can. J. Plant Sci.86(3), 809–815 (2006). [Google Scholar]
118.Selmar, D. & Kleinwaachter, M. Stress enhances the synthesis of secondary plant products: The impact of stress-related over-reduction on the accumulation of natural products. Plant Cell Physiol.54(6), 817–826. 10.1093/pcp/pct054 (2013). [DOI] [PubMed] [Google Scholar]
119.Yang, A. et al. Saponin seed priming improves salt tolerance in quinoa. J. Agron. Crop Sci.204(1), 31–39. 10.1111/jac.12229 (2017). [Google Scholar]
120.Baral, B., Silva, J. A. T. & Izaguirre-Mayoral, M. L. Early signaling, synthesis, transport and metabolism of ureides. J. Plant Physiol.193, 97–109. 10.1016/j.jplph.2016.01.013 (2016). [DOI] [PubMed] [Google Scholar]
121.Li, J. et al. The role of melatonin in salt stress responses. Int. J. Mol. Sci.20(7), 1735. 10.3390/ijms20071735 (2019). [DOI] [PMC free article] [PubMed] [Google Scholar]
122.Mascellani, A. et al. Moderate salinity stress affects expression of main sugar metabolism and transport genes and soluble carbohydrate content in ripe fig fruits (Ficus carica L. cv. Dottato). Plants10(9), 1–10. 10.3390/plants10091861 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]
123.Saito, T. et al. Salinity stress affects assimilate metabolism at the gene-expression level during fruit development and improves fruit quality in tomato (Solanum lycopersicum L.). J. Jpn. Soc. Hortic. Sci.77(1), 61–68. 10.2503/jjshs1.77.61 (2008). [Google Scholar]
124.Xiao, Y. et al. Mechanism of induced soluble sugar accumulation and organic acid reduction in plum fruits by application of melatonin. BMC Plant Biol.24(1), 1–14. 10.1186/s12870-024-05949-x (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]
125.Valifard, M., Mohsenzadeh, S., Kholdebarin, B. & Rowshan, V. Effects of salt stress on volatile compounds, total phenolic content and antioxidant activities of Salvia mirzayanii. S. Afr. J. Bot.93(2), 92–97. 10.1016/j.sajb.2014.04.002 (2014). [Google Scholar]
126.Tian, W. et al. Accumulation of wheat phenolic acids under different nitrogen rates and growing environments. Plants11(17), 1–9. 10.3390/plants11172237 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary Material 1^{(1.7MB, docx)}

Data Availability Statement

All data are available in the manuscript file.

[CR1] 1.Tabassum, M. et al. Chitosan modulated antioxidant activity, inorganic ions homeostasis and endogenous melatonin to improve yield of Pisum sativum L. accessions under salt stress. Sci. Hortic.323, 112509. 10.1016/j.scienta.2023.112509 (2024). [Google Scholar]

[CR2] 2.Chang, B., Yang, L., Cong, W., Zu, Y. & Tang, Z. The improved resistance to high salinity induced by trehalose is associated with ionic regulation and osmotic adjustment in Catharanthus roseus. Plant Physiol. Biochem.77, 140–148. 10.1016/j.plaphy.2014.02.001 (2014). [DOI] [PubMed] [Google Scholar]

[CR3] 3.Sheikhalipour, M. et al. Effect of melatonin foliar sprays on morphophysiological attributes, fruit yield and quality of Momordica charantia L. under salinity stress. Plant. Physiol. Biochem.205, 108194. 10.1016/j.plaphy.2023.108194 (2023a). [DOI] [PubMed] [Google Scholar]

[CR4] 4.Pal, S. C. et al. Combined use of seaweed extract and arbuscular mycorrhizal fungi for alleviating salt stress in bell pepper (Capsicum annuum L.). Sci. Hortic.325, 112597. 10.1016/j.scienta.2023.112597 (2024). [Google Scholar]

[CR5] 5.Liu, Y. et al. Exogenous serotonin improves salt tolerance in rapeseed (Brassica napus L.) seedlings. Agronomy11(2), 1–11. 10.3390/agronomy11020400 (2021). [Google Scholar]

[CR6] 6.Zulfiqar, F. et al. Melatonin seed priming improves growth and physio-biochemical aspects of Zinnia elegans under salt stress. Sci. Hortic.323, 112495. 10.1016/j.scienta.2023.112495 (2024). [Google Scholar]

[CR7] 7.Gohari, G. et al. Characterization of Octa-aminopropyl polyhedral oligomeric silsesquioxanes (OA-POSS) nanoparticles and their effect on sweet basil (Ocimum basilicum L.) response to salinity stress. Plant Physiol. Biochem.196, 89–102. 10.1016/j.plaphy.2023.01.019 (2023). [DOI] [PubMed] [Google Scholar]

[CR8] 8.Alisofi, S., Einali, A. & Sangtarash, M. H. Jasmonic acid-induced metabolic responses in bitter melon (Momordica charantia) seedlings under salt stress. J. Hortic. Sci. Biotechnol.95(2), 247–259. 10.1080/14620316.2019.1663135 (2020). [Google Scholar]

[CR9] 9.Sheikhalipour, M. et al. Exogenous melatonin increases salt tolerance in bitter melon by regulating ionic balance, antioxidant system and secondary metabolism-related genes. BMC Plant Biol.22(1), 1–17. 10.1186/s12870-022-03728-0 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR10] 10.Sheikhalipour, M. et al. Seedling nanopriming with selenium-chitosan nanoparticles mitigates the adverse effects of salt stress by inducing multiple defence pathways in bitter melon plants. Int. J. Biol. Macromol.242 (3), 124923. 10.1016/j.ijbiomac.2023.124923 (2023b). [DOI] [PubMed] [Google Scholar]

[CR11] 11.Sheikhalipour, M. et al. Chitosan–selenium nanoparticle (Cs–Se NP) foliar spray alleviates salt stress in bitter melon. Nanomaterials11(3), 1–22. 10.3390/nano11030684 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR12] 12.Zahra, N. et al. Serotonin improves plant growth, foliar functions and antioxidant defence system in Ethiopian mustard (Brassica carinata A. Br). S AFR. J. BOT.170 (2), 1–9. 10.1016/j.sajb.2024.05.002 (2024). [Google Scholar]

[CR13] 13.Kaur, H., Chowrasia, S., Gaur, V. S. & Mondal, T. K. Allantoin: Emerging role in plant abiotic stress tolerance. Plant Mol. Biol. Rep.39(1), 648–661. 10.1007/s11105-021-01280-z (2021). [Google Scholar]

[CR14] 14.Abbas, M. et al. Biochemical stress markers, antioxidants, and infectious wound-healing potential of UV irradiation and salt stress effects on the pre-treated seed of bitter melon (Momordica charantia L.). Dose. Response.19(4), 1–11. 10.1177/15593258211044062 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR15] 15.Singla, D., Sangha, M. K., Singh, M., Pathak, M. & Bala, M. Variation of mineral composition in different fruit parts of bitter gourd (Momordica charantia L.). Biol. Trace Elem. Res.201(10), 4961–4971. 10.1007/s12011-022-03546-3 (2023). [DOI] [PubMed] [Google Scholar]

[CR16] 16.Alomrani, S. O. et al. Effect of sodium hydrosulfide on physicochemical characteristics and melatonin mediated stress mitigation in bitter gourd (Momordica charantia L.) grown under lead stress. Sci. Hortic.323, 112547. 10.1016/j.scienta.2023.112547 (2024). [Google Scholar]

[CR17] 17.Chaudhury, P. Role of secondary metabolites of Momordica charantia in combating copper induced stress. AJABTR4(1), 5–29. 10.15864/ajabtr.412 (2023). [Google Scholar]

[CR18] 18.Ying, S. et al. Allantoin alleviates seed germination the rmoinhibition in Arabidopsis. Phyton91(9), 1893–1904. 10.32604/phyton.2022.022679 (2022). [Google Scholar]

[CR19] 19.Becker, L. C. et al. Final report of the safety assessment of allantoin and its related complexes. Int. J. Toxicol.29(3), 84–97. 10.1177/1091581810362805 (2010). [DOI] [PubMed] [Google Scholar]

[CR20] 20.Zhang, Y. M., Chu, Z. D., Feng, X., Sun, Y. X. & Gong, Y. H. Roles of allantoin in plant defense responses. Zhiwu Shengli Xuebao/Plant Physiol. J.53 (7), 1131–1138. 10.13592/j.cnki.ppj.2016.0512 (2017). [Google Scholar]

[CR21] 21.Fahad, S. et al. Suppressing photorespiration for the improvement in photosynthesis and crop yields: A review on the role of S-allantoin as a nitrogen source. J. Environ. Manag. 237, 644–651. 10.1016/j.jenvman.2019.02.082 (2019). [DOI] [PubMed] [Google Scholar]

[CR22] 22.Raihan, M. R. H., Rahman, M., Rastogi, A., Fujita, M. & Hasanuzzaman, M. Exogenous allantoin confers rapeseed (Brassica campestris) tolerance to simulated drought by improving antioxidant metabolism and physiology. Antioxidants12(8), 1–23. 10.3390/antiox12081508 (2023). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR23] 23.Liu, L. et al. Exogenous allantoin improves the salt tolerance of sugar beet by increasing putrescine metabolism and antioxidant activities. Plant Physiol. Biochem.154, 699–713. 10.1016/j.plaphy.2020.06.034 (2020). [DOI] [PubMed] [Google Scholar]

[CR24] 24.Irani, S., Lobo, J. M., Gray, G. R. & Todd, C. D. Allantoin accumulation in response to increased growth irradiance in Arabidopsis thaliana. Biol. Plant.62(1), 181–187. 10.1007/s10535-017-0747-2 (2018). [Google Scholar]

[CR25] 25.Dresler, S. et al. Allantoin attenuates cadmium-induced toxicity in cucumber plants. Ecotoxicol. Environ. Saf.170, 120–126. 10.1016/j.ecoenv.2018.11.119 (2019). [DOI] [PubMed] [Google Scholar]

[CR26] 26.Kaur, R., Chandra, J., Varghese, B. & Keshavkant, S. Allantoin: A potential compound for the mitigation of adverse effects of abiotic stresses in plants. Plants12(17), 1–21. 10.3390/plants12173059 (2023). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR27] 27.Watanabe, S. et al. The purine metabolite allantoin enhances abiotic stress tolerance through synergistic activation of abscisic acid metabolism. Plant Cell Environ.37(4), 1022–1036. 10.1111/pce.12218 (2014a). [DOI] [PubMed] [Google Scholar]

[CR28] 28.Lu, S. et al. Combined metabolomic and transcriptomic analysis reveals allantoin enhances drought tolerance in rice. Int. J. Mol. Sci.23(22), 1–20. 10.3390/ijms232214172 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR29] 29.Erland, L. A., Turi, C. E. & Saxena, P. K. Serotonin in plants: origin, functions, and implications. Serotonin10.1016/B978-0-12-800050-2.00002-4 (2019). [Google Scholar]

[CR30] 30.Zahra, N. et al. Regulation of photosynthesis under salt stress and associated tolerance mechanisms. Plant Physiol. Biochem.178, 55–69. 10.1016/j.plaphy.2022.03.003 (2022). [DOI] [PubMed] [Google Scholar]

[CR31] 31.Ahmad, I. et al. Integrated approaches for increasing plant yield under salt stress. Front. Plant Sci.14, 1–11. 10.3389/fpls.2023.1215343 (2023). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR32] 32.Pontes, C. V. S. et al. Exogenous serotonin and 24-Epibrassinolide boost root protection and suppress oxidative damages occasioned by severe water deficit in soybean seedlings. J. Plant Growth Regul.43(6), 1–11. 10.1007/s00344-023-11220-8 (2024). [Google Scholar]

[CR33] 33.Wan, J. et al. Comparative physiological responses and transcriptome analysis reveal the roles of melatonin and serotonin in regulating growth and metabolism in Arabidopsis. BMC Plant Biol.18(1), 1–14. 10.1186/s12870-018-1548-2 (2018). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR34] 34.Mukherjee, S., David, A., Yadav, S., Baluška, F. & Bhatla, S. C. Salt stress-induced seedling growth inhibition coincides with differential distribution of serotonin and melatonin in sunflower seedling roots and cotyledons. Physiol. Plant.152 (4), 714–728. 10.1111/ppl.12218 (2014). [DOI] [PubMed] [Google Scholar]

[CR35] 35.Akcay, U. C. & Okudan, N. Exogenous serotonin improves drought and salt tolerance in tomato seedlings. J. Plant Growth Regul.101(1), 239–249. 10.21203/rs.3.rs-2714889/v1 (2023). [Google Scholar]

[CR36] 36.Lichtenthaler, H. K. Chlorophylls and carotenoids: Pigments of photosynthetic biomembranes. Methods Enzymol.148, 350–382. 10.1016/0076-6879(87)48036-1 (1987). [Google Scholar]

[CR37] 37.Semer, J., Navrátil, M., Špunda, V. & Štroch, M. Chlorophyll fluorescence parameters to assess utilization of excitation energy in photosystem II independently of changes in leaf absorption. J. Photochem. Photobiol. B, Biol.197, 111535. 10.1016/j.jphotobiol.2019.111535 (2019). [DOI] [PubMed] [Google Scholar]

[CR38] 38.Schonfeld, M. A., Johnson, R. C., Carver, B. F. & Mornhinweg, D. W. Water relations in winter wheat as drought resistance indicators. Crop Sci.28(3), 526–531. 10.2135/cropsci1988.0011183X002800030021x (1988). [Google Scholar]

[CR39] 39.Ben Hamed, K., Castagna, A., Salem, E. A., Ranieri, A. & Abdelly, C. Sea fennel (Crithmum maritimum L.) under salinity conditions: A comparison of leaf and root antioxidant responses. J. Plant Growth Regul.53(3), 185–194. 10.1007/s10725-007-9217-8 (2007). [Google Scholar]

[CR40] 40.Irigoyen, J. J., Einerich, D. W. & Sanchez-Diaz, M. Water stress induced changes in concentrations of proline and total soluble sugars in nodulated alfalfa (Medicago sativa L.) plants. Physiol. Plant.84(1), 55–60. 10.1111/j.1399-3054.1992.tb08764.x (1992). [Google Scholar]

[CR41] 41.Paquin, R. & Lechasseur, P. Observation sur une method de dosage de la proline libre Dans les extrats deplants. Can. J. Bot.57(18), 1851–1854. 10.1139/b79-233 (1979). [Google Scholar]

[CR42] 42.Bor, J. Y., Chen, H. Y. & Yen, G. H. Evaluation of antioxidant activity and inhibitory effect on nitric oxide production of some common vegetables. J. Agric. Food Chem.54, 1680–1686 (2006). [DOI] [PubMed] [Google Scholar]

[CR43] 43.Masukasu, H., Karin, O. & Kyoto, H. Enhancement of anthocyanin biosynthesis by sugar in radish (Raphanus sativus) hypocotyl. Plant Sci.164, 259–265. 10.1016/S0168-9452(02)00408-9 (2003). [Google Scholar]

[CR44] 44.Sharma, T., Gamit, R., Acharya, R. & Shukla, V. J. Quantitative estimation of total tannin, alkaloid, phenolic, and flavonoid content of the root, leaf, and whole plant of Byttneria herbacea Roxb.. AYU (An International Quarterly Journal of Research in Ayurveda)42(3), 143–147. 10.4103/ayu.AYU_25_19 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR45] 45.Singleton, V. L. & Rossi, J. A. Colorimetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents. Am. J. Enol. Vitic.16(3), 144–153. 10.5344/ajev.1965.16.3.144 (1965). [Google Scholar]

[CR46] 46.Sini, K. R., Sinha, B. N. & Karpagavalli, M. Determining the antioxidant activity of certain medicinal plants of Attapady, (Palakkad), India using DPPH assay. Curr. Bot.1(1), 13–16 (2010). [Google Scholar]

[CR47] 47.Chen, S. et al. Arbuscular mycorrhizal fungi (AMF) increase growth and secondary metabolism in cucumber subjected to low temperature stress. Sci. Hortic.160, 222–229. 10.1016/j.scienta.2013.05.039 (2013). [Google Scholar]

[CR48] 48.Li, Z., Zhao, X., Sandhu, A. K. & Gu, L. Effects of exogenous abscisic acid on yield, antioxidant capacities, and phytochemical contents of greenhouse grown lettuces. J. Agric. Food Chem.58 (10), 6503–6509. 10.1021/jf1006962 (2010). [DOI] [PubMed] [Google Scholar]

[CR49] 49.Singh, R., Kumar, A., Giri, D. D., Bhuvaneshwari, K. & Pandey, K. D. Gas chromatography-mass spectrometry analysis and phytochemical screening of methanolic fruit extract of Momordica charantia. J. Recent Adv. Agric.1(4), 122–127 (2012). [Google Scholar]

[CR50] 50.Velikova, V. & Loreto, F. On the relationship between isoprene emission and thermotolerance in Phragmites australis leaves exposed to high temperatures and during the recovery from a heat stress. Plant Cell Environ.28(3), 318–327. 10.1111/j.1365-3040.2004.01314.x (2005). [Google Scholar]

[CR51] 51.Heath, R. L. & Packer, L. Photo-peroxidation in isolated chloroplasts: I. Kinetics and stoichiometry of fatty acid peroxidation. Arch. Biochem. Biophys.125(1), 189–198. 10.1016/0003-9861(68)90654-1 (1968). [DOI] [PubMed] [Google Scholar]

[CR52] 52.Bradford, M. M. Rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal. Biochem.72(1–2), 248–254. 10.1016/0003-2697(76)90527-3 (1976). [DOI] [PubMed] [Google Scholar]

[CR53] 53.Bergmeyer, H. U. Methods of enzymatic analysis 636–647 (Akademie Verlag, 1970). [Google Scholar]

[CR54] 54.Nakano, Y. & Asada, K. Hydrogen peroxide is scavenged by ascorbate-specific peroxidase in spinach chloroplasts. Plant Cell Physiol.22(5), 867–880. 10.1093/oxfordjournals.pcp.a076232 (1981). [Google Scholar]

[CR55] 55.Herzog, V. & Fahimi, H. D. A new sensitive colorimetric assay for peroxidase using 3,3’-diaminobenzidine as hydrogen donor. Anal. Biochem.55(2), 554–562. 10.1016/0003-2697(73)90144-9 (1973). [DOI] [PubMed] [Google Scholar]

[CR56] 56.Dhindsa, R. S., Plumb-Dhindsa, P. A. M. E. L. A. & Thorpe, T. A. Leaf senescence: Correlated with increased levels of membrane permeability and lipid peroxidation, and decreased levels of superoxide dismutase and catalase. J. Exp. Bot.32(1), 93–101. 10.1093/jxb/32.1.93 (1981). [Google Scholar]

[CR57] 57.Munns, R., Wallace, P. A., Teakle, N. L. & Colmer, T. D. Measuring soluble ion concentrations (Na, K, Cl) in salt-treated plants. In Plant Stress Tolerance, Methods in Molecular Biology Vol. 386 (ed. Sunkar, R.) 371–382 (Humana, 2010). [DOI] [PubMed] [Google Scholar]

[CR58] 58.Adesanwo, O. O., Ige, D. V., Thibault, L., Flaten, D. & Akinremi, W. Comparison of colorimetric and ICP methods of phosphorus determination in soil extracts. Commun. Soil Sci. Plant Anal.44(21), 3061–3075. 10.1080/00103624.2013.832771 (2013). [Google Scholar]

[CR59] 59.Gupta, P. k. Soil, plant, water and fertilizer analysis (2nd Ed.). Published by Agrobios (INDIA).147. (1999).

[CR60] 60.Zhou, H. et al. Insights into plant salt stress signaling and tolerance. J. Genet. Genomics51(1), 16–34. 10.1016/j.jgg.2023.08.007 (2024). [DOI] [PubMed] [Google Scholar]

[CR61] 61.Abdelkefi, N. et al. Enhanced salt stress tolerance in tomato plants following inoculation with newly isolated plant growth-promoting rhizobacteria. Sci. Hortic.328, 112921. 10.1016/j.scienta.2024.112921 (2024). [Google Scholar]

[CR62] 62.Shalaby, O. A. Moringa leaf extract increases tolerance to salt stress, promotes growth, increases yield, and reduces nitrate concentration in lettuce plants. Sci. Hortic.325, 112654. 10.1016/j.scienta.2023.112654 (2024). [Google Scholar]

[CR63] 63.Amerian, M., KhoramiVafa, M., Palangi, A., Gohari, G. & Ntatsi, G. The effect of different levels of urea and sodium selenate on the morphophysiological characteristics of garlic (Allium sativum L). Sci. Hortic.337, 1–14. 10.1016/j.scienta.2024.113469 (2024a). [Google Scholar]

[CR64] 64.Amerian, M., Palangi, A., Gohari, G. & Ntatsi, G. Humic acid and grafting as sustainable agronomic practices for increased growth and secondary metabolism in cucumber subjected to salt stress. Sci. Rep.14 (1), 1–18. 10.1038/s41598-024-66677-8 (2024b). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR65] 65.Gohari, G. et al. Titanium dioxide nanoparticles (TiO₂ NPs) promote growth and ameliorate salinity stress effects on essential oil profile and biochemical attributes of Dracocephalum moldavica. Sci. Rep.10 (1), 1–14. 10.1038/s41598-020-57794-1 (2020b). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR66] 66.Kanwal, R. et al. Exogenous ascorbic acid as a potent regulator of antioxidants, osmo-protectants, and lipid peroxidation in pea under salt stress. BMC Plant. Biol.24 (1), 1–16. 10.1186/s12870-024-04947-3 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR67] 67.Mohammadi, H. et al. Interaction of NaCl salinity and light intensity affect growth, physiological traits and essential oil constituents in Artemisia dracunculus L. (tarragon). Biochem. Syst. Ecol.107, 1–9. 10.1016/j.bse.2023.104626 (2023). [Google Scholar]

[CR68] 68.Irani, S. & Todd, C. D. Exogenous allantoin increases Arabidopsis seedlings tolerance to NaCl stress and regulates expression of oxidative stress response genes. J. Plant. Physiol.221, 43–50. 10.1016/j.jplph.2017.11.011 (2018). [DOI] [PubMed] [Google Scholar]

[CR69] 69.Wang, H. et al. Effects of salt stress on ion balance and nitrogen metabolism of old and young leaves in rice (Oryza sativa L). BMC Plant. Biol.12 (1), 1–11 (2012). http://www.biomedcentral.com/1471-2229/12/194 [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR70] 70.Dawood, M. F., Tahjib-Ul-Arif, M., Sohag, A. A. M., Abdel Latef, A. A. H. & Ragaey, M. M. Mechanistic insight of allantoin in protecting tomato plants against ultraviolet C stress. Plants10(1), 1–23. 10.3390/plants10010011 (2020). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR71] 71.Chowrasia, S. et al. Allantoin improves salinity tolerance in Arabidopsis and rice through synergid activation of abscisic acid and brassinosteroid biosynthesis. Plant Mol. Biol.112(3), 143–160. 10.1007/s11103-023-01350-8 (2023). [DOI] [PubMed] [Google Scholar]

[CR72] 72.Casartelli, A. et al. Opposite fates of the purine metabolite allantoin under water and nitrogen limitations in bread wheat. Plant Mol. Biol.99(4–5), 477–497. 10.1007/s11103-019-00831-z (2019). [DOI] [PubMed] [Google Scholar]

[CR73] 73.Arya, M., Kumar, G. & Giridhar, P. Serotonin-salt-stress model-induced cell growth via promoting an antioxidant system and secondary metabolites in Capsicum annuum cell suspension culture. ACS Omega10.1021/acsomega.4c05353 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR74] 74.Kaur, H., Mukherjee, S., Baluska, F. & Bhatla, S. C. Regulatory roles of serotonin and melatonin in abiotic stress tolerance in plants. Plant Signal. Behav.10(11), 1–8. 10.1080/15592324.2015.1049788 (2015). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR75] 75.Roychoudhury, A. Multifaceted roles of serotonin in plants. Young Scientist- Tomorrow’s Science Begins Today5(1), 26–35 (2021). [Google Scholar]

[CR76] 76.Erland, L. A. E. & Saxena, P. K. Beyond a neurotransmitter: The role of serotonin in plants. Neurotransmitter4(5), 1–12 (2017). [Google Scholar]

[CR77] 77.Danish, S. et al. The role of strigolactone in alleviating salinity stress in chili pepper. BMC Plant Biol.24(1), 1–13. 10.1186/s12870-024-04900-4 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR78] 78.Wu, Y. et al. 5-Aminolevulinic acid (ALA) alleviated salinity stress in cucumber seedlings by enhancing chlorophyll synthesis pathway. Front. Plant. Sci.9, 11–16. 10.3389/fpls.2018.00635 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR79] 79.Stefanov, M. A., Rashkov, G. D., Borisova, P. B. & Apostolova, E. L. Changes in Photosystem II complex and physiological activities in pea and maize plants in response to salt stress. Plants13(7), 1–17. 10.3390/plants13071025 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR80] 80.Shah, I. H. et al. Exploring the role of nitrogen and potassium in photosynthesis implications for sugar: Accumulation and translocation in horticultural crops. Sci. Hortic.327, 112832. 10.1016/j.scienta.2023.112832 (2024). [Google Scholar]

[CR81] 81.Liang, D. et al. Exogenous melatonin promotes biomass accumulation and photosynthesis of kiwifruit seedlings under drought stress. Sci. Hortic.246, 34–43. 10.1016/j.scienta.2018.10.058 (2019). [Google Scholar]

[CR82] 82.Imran, M. et al. Exogenous melatonin induces drought stress tolerance by promoting plant growth and antioxidant defence system of soybean plants. AoB Plants13(4), 1–12. 10.1093/aobpla/plab026 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR83] 83.Yu, Y. et al. The role of phyto-melatonin and related metabolites in response to stress. Molecules23(8), 1–15. 10.3390/molecules23081887 (2018). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR84] 84.Shiade, S. R. G. et al. Plant metabolites and signaling pathways in response to biotic and abiotic stresses: Exploring bio stimulant applications. Plant Stress12, 1–12. 10.1016/j.stress.2024.100454 (2024). [Google Scholar]

[CR85] 85.Abbas, A. et al. NaCl stress, tissue specific Na⁺ and K⁺ up-take and their effect on growth and physiology of Helianthus annuus L. and Solanum lycopersicum L. Sci. Hortic.326, 1–11. 10.1016/j.scienta.2023.112454 (2024). [Google Scholar]

[CR86] 86.Liao, Q. et al. Stomatal conductance modulates maize yield through water use and yield components under salinity stress. Agric. Water Manag.294, 108717 (2024). [Google Scholar]

[CR87] 87.Li, J. et al. Heterogeneous saline water irrigation improves stomatal and nonstomatal restrictions to decrease yield reduction threshold in cherry tomato. Sci. Hortic.326, 112788 (2024). [Google Scholar]

[CR88] 88.Zhang, D. et al. Unraveling the impacts of nano-scale carbon exposure on nitrogen metabolism during early seedling establishment in Zea mays L. roots. Plant Soil502(1), 245–265 (2024). [Google Scholar]

[CR89] 89.He, H. et al. Study on the mechanism of exogenous serotonin improving cold tolerance of rapeseed (Brassica napus L.) seedlings. J. Plant Growth Regul.94(2), 161–170. 10.1007/s10725-021-00700-0 (2021). [Google Scholar]

[CR90] 90.Ramakrishna, A., Giridhar, P. & Ravishanker, G. A. Phytoserotonin: A review. Plant Signal. Behav.6(6), 800–809. 10.4161/psb.6.6.15242 (2011). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR91] 91.Dehghanian, Z. et al. Role of neurotransmitters (biomediators) in plant responses to stress. Plants (Basel)13(22), 1–31. 10.3390/plants13223134 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR92] 92.Janah, I., Ben-Laouane, R., Elhasnaoui, A., Anli, M. & Meddich, A. The induction of salt stress tolerance by gibberellic acid treatment in Stevia rebaudiana Bertoni plants. Int. J. Plant Biol.15(2), 505–516. 10.3390/ijpb15020038 (2024). [Google Scholar]

[CR93] 93.Ferchichi, S. et al. Hordeum vulgare and Hordeum maritimum respond to extended salinity stress displaying different temporal accumulation pattern of metabolites. Funct. Plant Biol.45(11), 1096–109. (2018). [DOI] [PubMed] [Google Scholar]

[CR94] 94.Fatma, M. et al. Ethylene and sulfur coordinately modulate the antioxidant system and ABA accumulation in mustard plants under salt stress. Plants (Basel)10(1), 1–21. 10.3390/plants10010180 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR95] 95.Singh, A. & Satheeshkumar, P. K. Reactive Oxygen Species (ROS) and ROS Scavengers in Plant Abiotic Stress Response. In Stress Biology in Photosynthetic Organisms: Molecular Insights and Cellular Responses 41–63 (Springer Nature Singapore, 2024). [Google Scholar]

[CR96] 96.Eke, P. et al. Interaction of Melatonin with Reactive Oxygen Species in Plants. In Melatonin in Plants: A Regulator for Plant Growth and Development 137–171 (Springer Nature Singapore, 2023). [Google Scholar]

[CR97] 97.Gohari, G. et al. Interaction between hydrogen peroxide and sodium nitroprusside following chemical priming of Ocimum basilicum L. against salt stress. Physiol. Plant.168(2), 361–373. 10.1111/ppl.13020 (2020a). [DOI] [PubMed] [Google Scholar]

[CR98] 98.Celi, G. E., Gratão, P. L., Lanza, M. G. & Dos Reis, A. R. Physiological and biochemical roles of ascorbic acid on mitigation of abiotic stresses in plants. Plant Physiol. Biochem.202, 107970. 10.1016/j.plaphy.2023.107970 (2023). [DOI] [PubMed] [Google Scholar]

[CR99] 99.Yan, F. et al. Melatonin alleviates abscisic acid deficiency inhibition on photosynthesis and antioxidant systems in rice under salt stress. Phyton.93(7), 1421–1440. 10.32604/phyton.2024.053914 (2024). [Google Scholar]

[CR100] 100.Liang, K., Chen, Y., Hou, J. & Liu, F. Elevated CO2-conferred sodium homeostasis is linked to abscisic acid-mediated stomatal closure and signalling pathway in tomato plants. Hortic. Plant. J.10.1016/j.hpj.2024.01.005 (2024). [Google Scholar]

[CR101] 101.Singh Gill, S. & Tuteja, N. Cadmium stress tolerance in crop plants. Plant Signal. Behav.6(2), 215–222. 10.4161/psb.6.2.14880 (2011). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR102] 102.Gu, S., Jacobs, S. & Du, G. Efficacy, rate and timing of applications of abscisic acid to enhance fruit anthocyanin contents in ‘Cabernet Sauvignon’grapes. J. Hortic. Sci. Biotechnol.86(5), 505–510. 10.1080/14620316.2011.11512796 (2011). [Google Scholar]

[CR103] 103.Colak, N. The effect of exogenous N-acetylcysteine on the phenolic profile and antioxidant enzyme activities in two betalainic red beet (Beta vulgaris L.) leaves under salt stress. Acta Physiol. Plant.46(9), 81. 10.1007/s11738-024-03713-0 (2024). [Google Scholar]

[CR104] 104.Wang, J. et al. Transcriptome and metabolome analyses reveal complex molecular mechanisms involved in the salt tolerance of rice induced by exogenous allantoin. Antioxid11(10), 2045 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR105] 105.Bajwa, V. S. et al. Identification and characterization of serotonin as ananti-browning compound of apple and pear. Postharvest Biol. Technol.110, 183–189. 10.1016/j.postharvbio.2015.08.018 (2015). [Google Scholar]

[CR106] 106.Alam, R., Rasheed, R., Ashraf, M. A., Hussain, I. & Ali, S. Allantoin alleviates chromium phytotoxic effects on wheat by regulating osmolyte accumulation, secondary metabolism, ROS homeostasis and nutrient acquisition. J. Hazard. Mater.458, 131920. 10.1016/j.jhazmat.2023.131920 (2023). [DOI] [PubMed] [Google Scholar]

[CR107] 107.Rahneshan, Z., Nasibi, F. & Moghadam, A. A. Effects of salinity stress on some growth, physiological, biochemical parameters and nutrients in two pistachio (Pistacia vera L.) rootstocks. J. Plant Interact.13(1), 73–82. 10.1080/17429145.2018.1424355 (2018). [Google Scholar]

[CR108] 108.Heng, T. et al. The effects of soil salt stress on the Nitrogen uptake, yield response and Nitrogen use efficiency of cotton in arid areas. Agronomy14(1), 1–12. 10.3390/agronomy14010229 (2024). [Google Scholar]

[CR109] 109.Nam, M. H. et al. Metabolite profiling of diverse rice germplasm and identification of conserved metabolic markers of rice roots in response to long-term mild salinity stress. Int. J. Mol. Sci.16(9), 21959–21974. 10.3390/ijms160921959 (2015). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR110] 110.Jahan, B., Al Ajmi, M. F., Rehman, M. T. & Khan, N. A. Treatment of nitric oxide supplemented with nitrogen and sulfur regulates photosynthetic performance and stomatal behavior in mustard under salt stress. Physiol. Plant.168(2), 490–510. 10.1111/ppl.13056 (2020). [DOI] [PubMed] [Google Scholar]

[CR111] 111.Jahan, B. et al. Coordinated role of nitric oxide, ethylene, nitrogen, and sulfur in plant salt stress tolerance. Stresses1(3), 181–199. 10.3390/stresses1030014 (2021). [Google Scholar]

[CR112] 112.Erland, L. A. Views and perspectives on the indoleamines serotonin and melatonin in plants: Past, present and future. Plant Signal. Behav.19(1), 2366545 (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR113] 113.Krause, S. T. et al. The biosynthesis of thymol, carvacrol, and thymohydroquinone in Lamiaceae proceeds via cytochrome P450s and a short-chain dehydrogenase. Proc. Natl. Acad. Sci. U. S. A.118(52), 1–10. 10.1073/pnas.2110092118 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR114] 114.Sadeghi, A., Razmjoo, J., Karimmojeni, H., Baldwin, T. C. & Mastinu, A. Changes in secondary metabolite production in response to salt stress in Alcea rosea L.. Hortic.10(2), 1–26. 10.3390/horticulturae10020139 (2024). [Google Scholar]

[CR115] 115.Stefanakis, M. K. et al. The Effect of Salinity and Drought on the Essential Oil Yield and Quality of Various Plant Species of the Lamiaceae Family (Mentha spicata L., Origanum dictamnus L., Origanum onites L). Hortic10, 1–14. 10.3390/horticulturae10030265 (2024). [Google Scholar]

[CR116] 116.Petkova, N., Ivanova, L., Filova, G., Ivanov, I. & Denev, P. Antioxidants and carbohydrate content in infusions and microwave extracts from eight medicinal plants. J. Appl. Pharm. Sci.7 (10), 055–061. 10.7324/JAPS.2017.71008 (2017). [Google Scholar]

[CR117] 117.Zheng, Y., Dixon, M. & Saxena, P. Greenhouse production of Echinacea purpurea (L.) and E. angustifolia using different growing media, NO₃^–/NH₄⁺ ratios and watering regimes. Can. J. Plant Sci.86(3), 809–815 (2006). [Google Scholar]

[CR118] 118.Selmar, D. & Kleinwaachter, M. Stress enhances the synthesis of secondary plant products: The impact of stress-related over-reduction on the accumulation of natural products. Plant Cell Physiol.54(6), 817–826. 10.1093/pcp/pct054 (2013). [DOI] [PubMed] [Google Scholar]

[CR119] 119.Yang, A. et al. Saponin seed priming improves salt tolerance in quinoa. J. Agron. Crop Sci.204(1), 31–39. 10.1111/jac.12229 (2017). [Google Scholar]

[CR120] 120.Baral, B., Silva, J. A. T. & Izaguirre-Mayoral, M. L. Early signaling, synthesis, transport and metabolism of ureides. J. Plant Physiol.193, 97–109. 10.1016/j.jplph.2016.01.013 (2016). [DOI] [PubMed] [Google Scholar]

[CR121] 121.Li, J. et al. The role of melatonin in salt stress responses. Int. J. Mol. Sci.20(7), 1735. 10.3390/ijms20071735 (2019). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR122] 122.Mascellani, A. et al. Moderate salinity stress affects expression of main sugar metabolism and transport genes and soluble carbohydrate content in ripe fig fruits (Ficus carica L. cv. Dottato). Plants10(9), 1–10. 10.3390/plants10091861 (2021). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR123] 123.Saito, T. et al. Salinity stress affects assimilate metabolism at the gene-expression level during fruit development and improves fruit quality in tomato (Solanum lycopersicum L.). J. Jpn. Soc. Hortic. Sci.77(1), 61–68. 10.2503/jjshs1.77.61 (2008). [Google Scholar]

[CR124] 124.Xiao, Y. et al. Mechanism of induced soluble sugar accumulation and organic acid reduction in plum fruits by application of melatonin. BMC Plant Biol.24(1), 1–14. 10.1186/s12870-024-05949-x (2024). [DOI] [PMC free article] [PubMed] [Google Scholar]

[CR125] 125.Valifard, M., Mohsenzadeh, S., Kholdebarin, B. & Rowshan, V. Effects of salt stress on volatile compounds, total phenolic content and antioxidant activities of Salvia mirzayanii. S. Afr. J. Bot.93(2), 92–97. 10.1016/j.sajb.2014.04.002 (2014). [Google Scholar]

[CR126] 126.Tian, W. et al. Accumulation of wheat phenolic acids under different nitrogen rates and growing environments. Plants11(17), 1–9. 10.3390/plants11172237 (2022). [DOI] [PMC free article] [PubMed] [Google Scholar]

PERMALINK

Foliar application of allantoin and serotonin mitigates salinity stress in bitter melon (Momordica charantia L.)

Masoomeh Amerian

Gholamreza Gohari

Saeid Jalalihonarmand

Sima Panahirad

Georgia Ntatsi

Abstract

Supplementary Information

Introduction

Materials and methods

Plant material and treatments

Table 1.

Morphometric parameters, yield, firmness, TSS and stomatal resistance

Physiologic parameters

Photosynthetic pigments, SPAD, performance index (PIABS) and chlorophyll fluorescence parameter (Fv/Fm)

Relative water content (RWC) and electrolyte leakage (EL)

Measurement of biochemical properties

Leaf mineral concentrations

Statistical analysis

Results

Growth characteristics of bitter melon plant

Table 2.

Fig. 1.

Table 3.

Physiological characteristics

Photosynthetic pigments

Table 4.

Relative water content (RWC), electrolyte leakage (EL) and stomatal resistance

Table 5.

Antioxidant compounds and capacity, compatible metabolites, ascorbic acid, ABA and soluble proteins

Table 6.

Antioxidant enzymes (CAT, POX, SOD, APX), MDA and H2O2

Fig. 2.

Leaf K, Na, P and Cl concentration

Table 7.

Secondary metabolites content

Table 8.

Coumaric acid, furic acid, caffeic acid, gallic acid and cinnamic acid content

Table 9.

Fig. 3.

Discussion

Conclusion

Supplementary Information

Acknowledgements

Author contributions

Data availability

Declarations

Competing interests

Footnotes

References

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

Similar articles

Cited by other articles

Links to NCBI Databases

Photosynthetic pigments, SPAD, performance index (PI_ABS) and chlorophyll fluorescence parameter (Fv/Fm)

Antioxidant enzymes (CAT, POX, SOD, APX), MDA and H₂O₂