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. 2024 Nov 19;25:1104. doi: 10.1186/s12864-024-11054-y

Effects of exogenous melatonin on drought stress in celery (Apium graveolens L.): unraveling the modulation of chlorophyll and glucose metabolism pathways

Jiageng Du 1, Weilong Li 1, Zhuo Wang 1, Zhiheng Chen 1, Chao Wang 1, Wei Lu 1, Aisheng Xiong 2, Guofei Tan 3, Yangxia Zheng 1,✉, Mengyao Li 1,✉
PMCID: PMC11575136  PMID: 39563249

Abstract

Drought, a prevalent abiotic stressor, significantly impacts plant yield and quality. Melatonin (MT), a potent and economical growth regulator, plays a pivotal role in augmenting crop resilience against stress. This study investigated the efficacy of exogenous MT on drought-stressed celery seedlings by comprehensively analyzing phenotypic, physiological, and molecular attributes. The results revealed that exogenous MT mitigated celery seedling damage under drought stress, lowered malondialdehyde (MDA) concentrations, elevated oxidase activities, osmolyte levels, chlorophyll content, and augmented light energy conversion efficiency. Transcriptomic analysis demonstrated that MT could regulate chlorophyll synthesis genes (AgPORA1 and AgDVR2), contributing to heightened photosynthetic potential and increased drought tolerance in celery. Moreover, MT was found to modulate glycolytic pathways, upregulate pyruvate synthesis genes (AgPEP1 and AgPK3), and downregulate degradation genes (AgPDC2 and AgPDHA2), thereby promoting pyruvate accumulation and enhancing peroxidase activity and drought tolerance. The RNA-seq and qRT-PCR analyses demonstrated similar results, showing the same general expression trends. The study elucidates the physiological and molecular mechanisms underlying MT’s stress-alleviating effects in celery seedlings, offering insights into MT-based strategies in plant cultivation and breeding for arid environments.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-024-11054-y.

Keywords: Celery, Chlorophyll metabolism, Drought, Glycolysis, Melatonin

Introduction

As a consequence of global warming, droughts have shown increasing severity and have emerged as a major threat to global agricultural productivity. Reductions in crop yield due to drought are estimated to range from 30 to 90% [1]. Drought stress induces diverse physiological and metabolic alterations in plants, significantly disrupting their normal growth and developmental processes, leading to stunted growth and reduced growth rates. For instance, drought stress accelerates chlorophyll breakdown and impairs photosynthetic machinery, resulting in a substantial decrease in photosynthetic efficiency and exacerbating premature leaf senescence [2]. Drought-induced accumulation of reactive oxygen species (ROS) leads to oxidative injury of cellular lipid membranes, vital enzymes, proteins, and nucleic acids [3], which severely compromises energy generation and biochemical transformations in plants.

Following prolonged natural selection, plants have developed a range of defense and adaptation strategies in response to drought stress. Malondialdehyde (MDA) is one of the end products of lipid peroxidation reactions in cell membranes, and changes in its content can reflect the degree of lipid peroxidation in plant cell membranes and the plant’s response to stress conditions [2]. Multiple enzymes are involved in antioxidant defense, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), and glutathione reductase (GR), which form an activated antioxidative network under drought, effectively scavenging ROS to preserve cellular homeostasis [4]. Concurrently, they accumulate non-enzymatic antioxidants like AsA, GSH, and pyruvate, along with osmolytes such as mannitol, anthocyanins, and alkaloids, to sustain intracellular hydration and counteract oxidative pressures [5]. Furthermore, plants modulate the expression of pivotal genes (such as WRKY, MYB, HSPs, HSF, and NAC) to initiate intrinsic defense mechanisms tailored to the severity of drought stress. These genes encode proteins that play multiple essential roles, encompassing signal transduction, osmoprotectant synthesis, and antioxidant system establishment, thereby ensuring sustained plant survival and growth potential amidst drought [6]. Moreover, research has demonstrated that external applications of compounds, namely osmolytes like glycine betaine, antioxidants including glutathione, and plant growth regulators like melatonin, can substantially mitigate drought-induced harm. These compounds effectively increase the plants’ tolerance and adaptive capacity to drought [7].

Melatonin (N-acetyl-5-methoxytryptamine, MT) is an indispensable indoleamine to the life activities and biological processes of both animals and plants [8]. MT plays a pivotal role in plant growth and development, such as stimulating seed germination, facilitating fruit development, and maturation control [9, 10], which in turn enhances fruit quality and crop yield. Moreover, MT acts as a potent endogenous scavenger of free radicals, exhibiting antioxidant capabilities [11]. Research has shown that exogenous MT enhances the activity of enzymes such as SOD, POD, CAT, and APX, thereby reinforcing plant resilience [12]. Additionally, exogenous MT exerts protective effects against extreme temperatures [13], drought [14], salt toxicity [15], heavy metal stress [16] and so on, which is mediated by the modulation of key genes (such as bZIP, bHLH, WRKY, MYB, and HSPs) integral to abiotic stress-related signal transduction and metabolism. The potential of exogenous MT in mitigating drought stress in plants has been increasingly studied. Exogenous MT has been shown to mitigate drought-induced damage in crops like corn [17], cotton [18], and soybean [19] by regulating starch and sucrose metabolic pathways. Furthermore, MT enhances the drought tolerance of citrus [20] and grapevines [21] by stimulating flavonoid biosynthesis.

Celery (Apium graveolens L.) is a biennial herb of the Apiaceae family from the Mediterranean and Middle East regions and is cultivated worldwide [22]. The plant is rich in nutrients, encompassing vitamins, carotene, apigenin, and cellulose, among others, and exhibits pharmacological benefits such as blood pressure reduction, lipid regulation, and antioxidative properties [13, 23]. The root system of celery is characterized by its brevity and shallowness, which limits its water uptake efficiency; these characteristics result in low tolerance to drought stress and pose a significant challenge to celery cultivation. Consequently, enhancing celery’s drought tolerance is paramount for optimizing growth and securing crop yield quality. Previous studies have reported that celery combats oxidative stress induced by drought through elevated activity of antioxidant enzymes, namely SOD, POD, CAT, and APX [24]. Several stress-responsive genes, like AgNAC63 and AgNAC47, are upregulated and enhance drought tolerance in celery [25]. Nonetheless, past research has mostly focused on celery’s inherent mechanisms in responding to drought, while the explicit mechanisms and impacts of exogenous treatments on augmenting its drought resilience remain poorly understood. Exogenous MT has proven efficacious in enhancing plant resistance to abiotic stresses, notably drought, primarily by stimulating the antioxidant defense system [11, 26]. However, the intricate specifics of MT’s regulatory role in mediating tolerance responses across diverse plant species, particularly in celery drought stress response, are yet to be fully elucidated. Hence, this investigation aims to explore the physiological and molecular mechanisms underlying the effects of exogenous MT on celery seedlings’ reaction to drought stress, encompassing the antioxidant system’s response, variations in photosynthetic efficiency, accumulation of osmolytes, and regulation of pertinent gene expressions. The findings provide novel theoretical frameworks and practical strategies for bolstering celery’s drought tolerance.

Materials and methods

Plant material and experimental design

The celery variety ‘Jinyun Baoqin’ (seeds obtained from Tianjin Cultivated Seed Co., Ltd.) was used as the plant material. Celery seeds were disinfected, soaked, and sprouted in 5 cm × 5 cm × 5 cm nutrient bowls containing a specific growth medium. Subsequently, the Petri dishes were placed in an artificial climate incubator under the following conditions: temperature of 23 °C/18°C (day/night), humidity of 70%, photoperiod of 14 h light/10 h dark, and light intensity of 1000 µmol m− 2 s− 1. Seedlings were then transplanted into 10 cm × 10 cm × 10 cm pots after 30 days of growth. After another 50 days, consistent celery seedlings exhibiting uniform growth were selected and subjected to foliar application of MT solutions at concentrations of 0, 25, 50, 100, 150, and 200 µM, which were administered once daily over 7 days. At 9:00 am on the second day following the final MT treatment, the roots were irrigated with a 20% PEG 6000 solution to induce water stress, marking the onset of drought stress (Day 0). 300 mL of the same solution was applied every 3 days for a total of four times. Following a 12-day cultivation period, plant height, dry weight, and fresh weight were measured, and various physiological parameters were measured from both leaves and leaf stalks.

Measurement of growth and physiological indicators

Plant height was measured using a ruler; the dry weight was determined after drying at 60 °C [15]. Malondialdehyde (MDA) content was quantified via the thiobarbituric acid assay [27], while proline (Pro) content was assessed using the acid-indanhydrin technique (Bates et al., 1973). Moreover, activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were assayed using nitroblue tetrazolium, potassium permanganate titration, and guaiacol oxidation assays, respectively [13]. Melatonin content was determined using a plant melatonin (MT) ELISA kit (Chongqing Bonoheng Biotechnology Co., Ltd.).

Determination of chlorophyll content, fluorescence parameters, and observation of anatomical structure

The acetone-ethanol mixture method [28] was used to measure the chlorophyll content. Chlorophyll fluorescence parameters were measured using a chlorophyll fluorometer (PAM-2500) following a 1-hour dark adaptation period. Celery leaf samples were immersed in a 50% FAA fixative solution composed of formalin, glacial acetic acid, and 50% ethanol in a 1:1:18 ratio, and fixed at 4 °C for 24 h. Afterward, the samples were subjected to ethanol dehydration, were embedded in paraffin wax, and sectioned tissues were stained with safranin and solid green (1% and 0.5%, respectively). Cross-sectional blade morphology was observed under an optical microscope, and images were captured and analyzed utilizing an imaging system (Nikon DS-U3, Nikon Corporation, Tokyo, Japan). Six replicates were measured for each treatment.

RNA extraction and sequencing

The RNA samples were extracted from the leaves of celery plants under different treatments. Total RNA was extracted from leaf tissues using a Plant Total RNA Isolation Kit (Sangon Biotech, Shanghai, China). In addition, RNA quality was detected by a NanoPhotometer spectrophotometer (IMPLEN, CA, USA), Qubit 2.0 Fluorometer (Life Technologies, Carlsbad, CA, USA), and an Agilent Bioanalyzer 2100 system (Agilent Technologies, Santa Clara, CA, USA). The cDNA (~ 200 bp) was screened using AMPure XP beads. After amplification and purification, cDNA libraries were obtained and sequenced using the Illumina HiSeqTM 2000 system (Illumina, San Diego, CA, USA) [17].

Quantitative real-time RCR (qRT-PCR) analysis

For qRT-PCR, RNA was extracted using a Trizol Total RNA Extraction Kit (Sangon Biotech, Shanghai, China) and reverse transcribed using an Evo M-MLV RT Mix Kit with gDNA Clean (Accurate Biotechnology, Hunan, China). The primers are listed in Table S1. qRT-PCR was conducted using a BioEasy Master Mix (SYBR Green) Kit (Bioer, Hangzhou, China) and a C1000 TouchChihermal Cycler system (Bio-Rad). The amplification procedure was 95℃ pre-denaturation for 1 min; 95℃ denaturation 10 s, annealing at 58℃ for 15 s, and the number of amplification cycles was 39 cycles. All tested transcripts were normalized to the reference gene AgActin, and relative expression levels were calculated according to the 2−∆∆Ct method [29]. Three biological and technical replications were performed.

Statistical analysis

The data were analyzed with Excel 2020 (Microsoft Inc., Redmond, USA) and SPSS 22 (SPSS Inc., Chicago, USA) using an analysis of variance (ANOVA), followed by Duncan’s significant difference test at p < 0.05. The graphs were constructed using Origin 2020 (Electronic Arts Inc., San Francisco, CA, USA).

Results

Growth and physiological analysis of MT-treated celery seedlings under drought stress

Under drought conditions, celery foliage exhibited wilting and yellowing, with the petioles failing to maintain upright posture and drooping. Concurrently, root systems displayed enhanced development, accompanied by suppressed overall plant growth. Application of moderate concentrations of MT (50, 100, and 150 µM) effectively mitigated these effects. However, the higher concentration of MT (200 µM), as well as the lower dose (50 µM) proved less efficacious (Fig. 1A). Compared to the CK group (control, without drought stress), the groups subjected to drought stress exhibited a 35.63% reduction in plant height. However, treatment with 100 µM MT led to a milder decrease of 7.61% in plant height (Fig. 1B). Similarly, drought stress induced significant reductions in both fresh and dry weights of celery plants, which was mitigated by MT application, especially at the concentration of 100 µM (Fig. 1C and D).

Fig. 1.

Fig. 1

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Effects of exogenous MT on celery growth indexes under drought stress. (A) Phenotypic characteristics of celery seedlings under drought stress. (B) Plant height, (C) Fresh weight, (D) Dry weight. Each bar represents the mean ± SD line, and t-test with a significance level of 0.05 (p < 0.05). CK: control; D: drought stress treatment; M25: 25 µM exogenous MT + drought stress; M50: 50 µM exogenous MT + drought stress; M100: 100 µM exogenous MT + drought stress; M150: 150 µM exogenous MT + drought stress; M200: 200 µM exogenous MT + drought stress

Under drought stress conditions, the contents of Pro, MDA, and endogenous MT in MT-treated groups significantly rose, exhibiting increases of 41.76, 361.90, and 34.78% compared to the CK group, respectively. Exogenous MT application resulted in further elevations in Pro and endogenous MT levels, whereas MDA content decreased. The highest efficacy was observed at 100 µM, resulting in Pro and endogenous MT contents increasing by 10.79% and 112.90%, respectively, relative to the drought treatment (D group), and MDA content decreasing by 57.32% (Fig. 2A-C). Moreover, drought stress significantly augmented the activities of the three antioxidant enzymes SOD, POD, and CAT, which showed significantly higher levels than the CK group, with a difference of 34.44, 78.90, and 7.04%, respectively. MT treatment further enhanced these enzymes’ activities, with 100 µM remaining the optimum concentration. Compared to the drought stress group, antioxidant enzyme activities rose by 26.11, 28.72, and 44.74%, respectively, in 100 µM MT group (Fig. 2D-F). Therefore, exogenous MT application was found to enhance the comprehensive drought tolerance of celery, with 100 µM MT demonstrating the exhibiting the most pronounced mitigation of growth inhibition.

Fig. 2.

Fig. 2

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Effects of drought stress on physiological characteristics of celery. (A) proline (Pro), (B) malondialdehyde (MDA), (C) melatonin (MT), (D) superoxide dismutase (SOD), (E) peroxidase (POD), (F) catalase (CAT). Each error line represents the mean ± SD, and t-test with a significance level of 0.05 (p < 0.05). CK: control; D: drought stress treatment; M25: 25 µM exogenous MT + drought stress; M50: 50 µM exogenous MT + drought stress; M100: 100 µM exogenous MT + drought stress; M150: 150 µM exogenous MT + drought stress; M200: 200 µM exogenous MT + drought stress

Effects of exogenous MT on chlorophyll and fluorescence parameters of celery under drought stress

To investigate the effects of exogenous MT on celery under drought stress, the photosynthetic attributes of celery under control conditions (CK), drought (D), and 100 µM MT + drought (MD) treatments were compared. Under CK group, celery leaves displayed a total chlorophyll content of 2.01 mg·g⁻¹. Drought stress induced a marked reduction in chlorophyll content to 1.23 mg g⁻¹. However, this decline was notably mitigated by MT application, reaching 1.73 mg g⁻¹ (Fig. 3A). The parameters of chlorophyll fluorescence kinetics also revealed variations in celery under drought stress. Specifically, the Fv/Fm, qP, ETR, and Y(II) values showed significant decreases under drought stress compared to CK. Conversely, NPQ and Y(NPQ) were substantially elevated. MT treatment effectively alleviated the decrease in Fv/Fm, qP, ETR, and Y(II), and suppressed the increase in NPQ and Y(NPQ) (Fig. 3B). These findings suggest that MT enhances chlorophyll content and PSII light-energy conversion efficiency in drought-stressed celery, concurrently reducing heat dissipation of absorbed light energy by antennae pigments.

Fig. 3.

Fig. 3

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Effects of chlorophyll content (A) and fluorescence kinetic parameters (B) on celery under drought stress. Each error line represents the mean ± SD, and t-test with a significance level of 0.05 (p < 0.05)

Effects of exogenous MT on the anatomical structure of celery leaves under drought stress

The morphology and stomatal movement of celery leaves under drought stress were observed. Following exposure to drought stress, the mesophyll thickness of the leaves from the MD and D groups was significantly reduced compared with those of the CK group (Fig. 4A, E, F, G). The spongy and palisade tissue in CK and MD leaves were arranged in regular shapes, and the upper and lower epidermal cells were full-shaped. In leaves from the D group, the spongy, palisade, and upper and lower epidermal cells became thin and exhibited severe cell dehydration (Fig. 4H–J). The stomata also demonstrated significant variations among the three treatment groups (Fig. 4B-D). In response to drought stress, the stomatal width, length, and area of leaves treated with MD were higher than those of the control group. In contrast, D leaves were dehydrated and wilted, having lost water in guard cells, resulting in the stomata closing. The width and area of the stomata of the D group were smaller than those of the CK group.

Fig. 4.

Fig. 4

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Effects of exogenous MY on the anatomical structure of celery leaves under drought stress. (A) Mesophyll thickness, (B) Stomatal length, (C) Stomatal width, (D) Stomatal area, (E) CK leaf plan, (F) D leaf plan, (G) MD leaf plan, (H) CK leaf section, (I) D leaf section, (J) MD leaf section. Each error line represents the mean ± SD, and t-test with a significance level of 0.05 (p < 0.05). Scale bar = 75 μm

Transcriptome sequencing DEGs analysis

Transcriptomic profiling was conducted across three distinct treatments utilizing the Illumina HiSeq 4000 platform. The results yielded 484 million raw reads, with 95.84% successfully aligned to the celery genome (Table S2). In addition, correlation analysis and PCA analysis revealed substantial variations among the treatment groups, with high intra-treatment reproducibility across the triple biological replicates (Fig. S1).

The FPKM value was employed for transcript quantification normalization to identify differentially expressed genes (DEGs), as shown in Fig. 5. A total of 7,974 DEGs were found between the drought treatment group (D) and the control group (CK). Moreover, 5,487 distinct DEGs were identified between the CK group and the moderate drought treatment with MD group. A total of 3,746 DEGs were found between the D group and the MD group. Notably, the intersection of the CK and D groups, as well as between the CK and MD groups, comprised the highest number of shared DEGs at 3,072. MT application led to a reduction of approximately 1,252 DEGs in the MD group compared to the CK group, with only 825 common DEGs between the D and MD groups (Fig. 5A). The hierarchical clustering heatmap (Fig. 5B) visually represented the DEG expression profiles across treatments based on the expression matrix, illustrating groups of genes highly expressed in the D and MD Groups, compared to the CK group. The results revealed distinct variations between the D and MD groups. Advanced K-means clustering analysis (Fig. 5C, Table S3) stratified all DEGs into three distinctive subclusters, demonstrating variable expression trends. Subcluster 1, encompassing 4,400 genes, showed upregulation under D and MD group, with MD displaying relatively reduced expression levels. Conversely, subcluster 3 (70 genes), showed down-regulated D and MD group, with MD displaying relatively increased expression levels. Additionally, subcluster 2 (1,531 genes) remained stable under D group, with MD showing relatively reduced expression levels. Collectively, these findings imply that MT potentially modulates the adaptive mechanisms of celery to drought stress by regulating specific DEGs’ expression profiles.

Fig. 5.

Fig. 5

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Distribution characteristics of differentially expressed genes (DEGs) in three different comparison groups. (A) UpSet Plot analysis of the number of DEGs for any two different comparisons. (B) Clustering of the DEGs’ transcript abundance in all samples. (C) K-means clustering of gene expression trends. The expression profile of each gene in each subpopulation is shown as a gray line, and the average expression profile of all the genes in each sample is shown in blue

DEGs annotation analysis

In order to further elucidate the response to MT, the biological functions, GO, and KEGG enrichment analyses of DEGs were performed in MT-treated celery seedlings under drought stress (Fig. 6). The GO terms of DEGs in “D vs CK” were significantly enriched in “response to stimulus”, “membrane” and “cell periphery” (Fig. 6A). The GO terms of DEGs in “MD vs CK” were significantly enriched in “catalytic activity”, “membrane” and “cell periphery” (Fig. 6B). The GO terms of DEGs in “MD vs D” were significantly enriched in “response to stimulus,” “response to chemical,” and “response to stress” (Fig. 6C).

Fig. 6.

Fig. 6

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Gene Ontology (GO) enrichment analysis of DEGs among comparison pairs. (A) GO pathway analysis of DEGs in “D vs CK”. (B) GO pathway analysis of DEGs in “MD vs CK”. (C) GO pathway analysis of DEGs in “MD vs D”. (D) KEGG pathway analysis of DEGs in “D vs CK”. (E) KEGG pathway analysis of DEGs in “MD vs CK”. (F) KEGG pathway analysis of DEGs in “MD vs D”

KEGG pathway enrichment analysis revealed that the group comparisons “D vs CK”, “MD vs CK”, and “MD vs D” were enriched in diverse pathways implicated in plant stress responses and metabolism (Fig. 6D–F). Specifically, the recurrent appearance of the “Glycolysis, Citrate cycle, and Pyruvate metabolism” pathway between various groups (“D vs CK” and “MD vs D”) implies that glycolysis plays a central role in MT-induced drought tolerance. The beneficial effects of MT on drought stress in celery may be mediated by modulating energy generation and signaling. In addition, the abundance of photosynthetic-related pathways, such as “photosynthesis” and “photosynthesis-antenna proteins”, suggests that MT may affect photosynthetic pathways to alleviate drought stress.

Analysis of the chlorophyll metabolism pathway

KEGG pathway analysis revealed that exogenous MT may regulate genes involved in carbon fixation and chlorophyll metabolism within photosynthetic organisms. The majority of these genes were upregulated in response to exogenous MT administration (Fig. 7A), augmenting the photosynthetic capacity in plants, and thereby enhancing their drought tolerance. The key enzymes AgHEMA1 and AgHEMG2, responsible for protoporphyrin IX synthesis were significantly downregulated under drought stress. MT application reversed this trend, increasing the expression of AgHEMA1 and AgHEMG2 genes compared to drought-stressed plants. Chlorophyll synthesis diverges into two pathways at protoporphyrin IX: one leading to heme and photopigment production via the iron-dependent route, and another directed towards chlorophyll formation via magnesium incorporation. Heme exerts a suppressive effect on chlorophyll biosynthesis. Drought elevates AgHEMH1 expression, a pivotal gene in heme synthesis, leading to increased heme levels and subsequent chlorophyll reduction. In contrast, MT group was observed to have a complex effect on gene expression. Specifically, it suppressed AgHEMH1 expression while increasing the expression of AgPORA1 and AgDVR2, which are pivotal in chlorophyll biosynthesis. However, the significance of this effect on chlorophyll accumulation remains to be further validated. Moreover, drought stress was found to stimulate the expression of genes associated with the degradation of primary fluorescent chlorophyll metabolites, such as AgPAO1 and AgPCCR1, leading to a decrease in light energy conversion efficiency. While MT intervention did show a tendency to repress the expression of these drought-induced genes, the precise mechanism by which MT sustains high light-to-energy conversion rates and photosynthetic performance remains to be elucidated. Thus, further research is needed to fully understand the role of MT in regulating these processes.

Fig. 7.

Fig. 7

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Metabolite transformation and gene expression changes in the porphyrin and chlorophyll metabolism pathway under drought stress. (A) Metabolite transformation and gene expression changes in the chlorophyll metabolism pathway under drought stress. Red (up-tuned) and blue (down-tuned) in the heat map represent gene expression trends. The heatmap data are derived from FPKM values after applying log scale and row scale transformations. (B) qRT-PCR analysis of genes in key pathways under drought treatment. Each error line represents the mean ± SD, and t-test with a significance level of 0.05 (p < 0.05). The column shape represents the relative expression of genes in qRT-PCR, and the broken line represents the RNA-seq data

To confirm the accuracy and reproducibility of the RNA-seq data, six genes involved in chlorophyll metabolism were selected for qRT-PCR (Fig. 7B). The results indicated a decrease in expression of AgDVR2 and AgCHLI1, pivotal to chlorophyll synthesis, by 3.6-fold and 2.9-fold, respectively, under drought conditions. Exogenous MT supplementation elevated their expression by 1.11-fold and 1.46-fold, respectively. These outcomes aligned with the RNA-seq dataset trends, supporting our initial transcriptomic analyses. Consequently, exogenous MT aids celery plants in maintaining chlorophyll synthesis during drought, enhancing photosynthetic capability and light-energy conversion efficiency, which confers heightened drought tolerance.

Analysis of the glycolysis metabolism pathway

In our detailed examination of the glycolysis pathway (Fig. 8A), exogenous MT administration significantly enhanced the expression of enzyme-coding genes integral to the conversion of glucose into pyruvate, specifically AgPFP1, AgHK1, AgPEP1, and AgPK3, thereby facilitating the efficient conversion of glucose into pyruvate. This acceleration of the rate of initial energy production reflects the metabolic adjustment under MT influence. Concurrently, most enzyme-coding genes in the pyruvate metabolic pathway within the TCA cycle were downregulated under MT treatment. Relative to the key genes driving pyruvate degradation, AgPDC2 and AgPDHA2, alongside other enzymes like AgPDHA1, AgCS1, and AgACO1 in drought-stressed (D) and MT-treated drought-stressed (MD) groups, pyruvate utilization within the TCA cycle was significantly inhibited, effectively decelerating the rate of pyruvate’s oxidative consumption. Therefore, exogenous MT not only boosts pyruvate biosynthesis but also increases intracellular pyruvate levels by decreasing its expenditure. These changes represent a crucial metabolic adjustment for activating the antioxidant defense system in plants and facilitating ROS detoxification, augmenting their adaptability and drought tolerance.

Fig. 8.

Fig. 8

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Metabolite transformation and gene expression changes in the glucose metabolism pathway under drought stress. (A) Metabolite transformation and gene expression changes in the pyruvate metabolism pathway under drought stress. Red (up-tuned) and blue (down-tuned) in the heat map represent gene expression trends. The heatmap data are derived from FPKM values after applying log scale and row scale transformations. (B) qRT-PCR analysis of genes in key pathways under drought treatment. Each error line represents the mean ± SD, and t-test with a significance level of 0.05 (p < 0.05). The column shape represents the relative expression of genes in qRT-PCR, and the broken line represents the RNA-seq data

To further validate the gene transcript abundance in RNA-seq, six glycolysis-related genes were subjected to qRT-PCR validation (Fig. 8B). Experimental data confirmed that MT elevated the expression of pyruvate synthesis-related genes AgPFP1, AgPEP1, and AgPK3 by 1.79-fold, 1.56-fold and 1.41-fold, respectively. The expression of pyruvate degradation genes, AgPDC2, AgMDH5, and AgACO2, decreased by 1.89-fold, 1.37-fold, and 1.72-fold, respectively. The above results aligned closely with the RNA-seq analytical trends. Collectively, these findings robustly affirm the efficacy of exogenous MT in enhancing celery’s drought tolerance through precise modulation of key glycolytic pathway genes.

Discussion

Drought imposes significant abiotic stress and unfavorably influences plant morphology and physiology, hindering growth and development [30]. Our investigation revealed that drought instigates phenotypic changes in celery, such as leaf wilting, yellowing, growth inhibition, and modifications to root architecture. The administration of exogenous MT notably ameliorated these detrimental impacts, not only mitigating the decline in plant stature but also efficaciously alleviating drought-induced reductions in fresh and dry biomass. The 100 µM MT treatment exhibited the most pronounced efficacy, suggesting that this concentration was optimal for enhancing celery’s drought tolerance. It’s worth noting that PEG 6000, while effective in creating an osmotic stress environment that mimics drought conditions, does not fully replicate the complexity of natural drought [5]. Natural drought involves gradual soil moisture depletion, altered soil microbial activity, and changes in soil chemistry, which are not fully captured by PEG 6000 treatment. In conclusion, while our study provides valuable insights into the role of exogenous MT in alleviating drought stress in celery seedlings, the potential limitations of using PEG 6000 as a drought stress simulator should be carefully considered in future research endeavors.

Under drought, plant tissue water and chlorophyll content decline, leading to ROS accumulation and MDA formation; these changes cause membrane lipid peroxidation and disrupt cellular membrane integrity, impairing celery seedling growth. MT is recognized for its comprehensive antioxidative capabilities and bolsters the activity of antioxidant enzymes in celery seedlings under drought, aiding ROS neutralization [31]. Our study revealed that exogenous MT elevated water content, proline, and endogenous MT levels in drought-stressed celery seedlings, further augmenting antioxidant enzyme activities and curtailing ROS and MDA build-up. These outcomes imply that MT and its derivatives function as free radical scavengers to alleviate celery seedling drought stress. In accordance with our study, past research has shown that exogenous MT markedly enhances the growth and stress resilience of maize and wheat by reinforcing their ROS and MDA detoxification mechanisms under drought conditions [32, 33]. These findings underscore the potential of appropriately applied exogenous MT to alleviate drought-induced growth impediments via physiological adjustments.

The application of exogenous MT can increase the photosynthetic efficiency of plants under water deficit conditions [34]. A comparative analysis between drought-stressed plants (group D) and those treated with MT under drought (group MD) unveiled that the latter possessed broader stomatal pores, augmented leaf thickness, and compact palisade and spongy parenchyma. Thus, group MD effectively regulated transpiration and preserved cellular integrity, whereas the anatomical structure of group D plants exhibited significant impairment. Under drought stress, stomatal closure reduces water evaporation. When the stomata are closed, their length is greater than when they are open. After melatonin treatment, the stomata open and their length decreases accordingly. To ensure the normal growth of plants under drought stress, leaves exhibit adaptive features where stomatal area increases and density decreases to prevent water loss and facilitate carbon dioxide absorption [35]. Exogenous melatonin treatment can induce the first step in opening closed stomata, thereby increasing the stomatal area. Exogenous MT is documented to conserve the chloroplast stroma and leaf organization [33], fostering cellular expansion and water conservation, averting the breakdown of photosynthetic pigments, and increasing the activity of electron transport [36]. Drought stress disrupts electron transport dynamics, diminishing photochemical efficiency and exacerbating the dissipation of surplus energy as heat [37, 38], which hampers ATP and NADPH synthesis and instigates ROS overproduction [39]. In the context of our study, celery seedlings receiving MT therapy during drought stress demonstrated heightened Fv/Fm, Y(II), and qP parameters compared to the drought-only control group, attesting to MT’s potency in preserving electron transport functionality and suppressing ROS genesis. This aligns with previous research confirming MT’s ROS-scavenging properties [32]. Collectively, these insights underscore MT’s capacity to reinforce light capture and energy transformation capabilities in celery plants exposed to drought stress.

Photosynthesis is the major process responsible for energy production for plant growth and maturation and is intimately tied to carbohydrate output. Chlorophyll is a primary photosynthetic pigment and is indispensable for photon harvesting [10, 40]. Specifically, a marked elevation in AgHEMH1 expression, which plays an essential role in heme biosynthesis, was observed under drought stress. The elevated AgHEMH1 expression diverted protoporphyrin IX metabolism toward heme synthesis as opposed to chlorophyll production [41]. However, the introduction of exogenous MT effectively reversed this redirection. Following MT intervention, AgHEMH1 transcription subsided, accompanied by a rise in the expression of chlorophyll synthesis-critical genes AgPORA1 and AgDVR2. This adjustment promoted chlorophyll synthesis in celery exposed to drought, alleviating the constraints on photosynthesis and assuring the proficient capture and utilization of light energy. Hence, MT’s regulatory influence on these key genes not only mitigates the negative impact of drought on chlorophyll production but also sustains the efficiency of photosynthetic light energy conversion in stressed plants.

Drought stress initiates the production of O2− and H2O2 within mitochondria and chloroplasts, alongside an escalation of ROS levels in both the cytoplasm and nucleus [42]. ROS operates as a signaling cue, detecting drought stress and instigating the plant’s protective mechanisms. Furthermore, exogenous MT amplifies the activity of antioxidant enzymes such as SOD, POD, and CAT. Previous research reported that MT non-enzymatically scavenges ROS generated by stress and restrains ROS production, concurrently upregulating genes coding for SOD, POD, CAT, APX, and more. Thus, oxidative stress due to lipid peroxidation is mitigated, preserving plant growth and development [43, 44]. KEGG pathway analyses revealed that MT increases pyruvate levels in drought-stressed plants by upregulating genes involved in pyruvate synthesis (including AgPFP1, AgHK1, AgPEP1, and AgPK3) while suppressing those responsible for pyruvate degradation (like AgPDC2, AgPDHA2). MT also non-enzymatically scavenges ROS generated by drought, protecting cells from oxidative damage [45].

In summary, exogenous MT successfully enhances the chlorophyll content in leaves under drought conditions by upregulating genes associated with chlorophyll biosynthesis, thereby bolstering the functionality of the photosynthetic machinery and fostering efficient carbohydrate production. Concurrently, MT facilitates glucose breakdown, augments pyruvate accumulation, and enhances antioxidant synthesis; consequently, ROS is rapidly eliminated, effectively alleviating cellular oxidative stress induced by drought (Fig. 9). These intertwined mechanisms not only counteract the inhibitory effects of drought on photosynthesis but also significantly alleviate oxidative stress. These findings establish a firm theoretical and practical foundation for leveraging MT as a powerful exogenous regulator in improving crop tolerance to drought conditions.

Fig. 9.

Fig. 9

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MT enhances drought stress tolerance of celery by regulating chlorophyll and glucose. The orange arrow depicts upregulation of gene expression, and the blue arrow depicts downregulation of gene expression

Conclusion

This study demonstrates the ability of MT to enhance drought tolerance in celery plants. Drought stress significantly disrupts the physiological and biochemical processes in celery, inhibiting its growth and development. At the physiological level, exogenous MT increases plant drought tolerance by enhancing antioxidant enzyme activities, preserving photosynthetic pigments, safeguarding leaf integrity, and augmenting photosynthetic efficiency. On a molecular level, it stimulates the expression of chlorophyll synthesis and stress resistance genes, thereby boosting photosynthesis and antioxidant capabilities, effectively mitigating the detrimental impacts of drought stress. Collectively, the elucidated physiological and molecular mechanisms governing the impacts of MT on celery’s drought response provide a fresh perspective for the cultivation of celery under drought stress and the development of superior, drought-tolerant cultivars. This offers substantial potential for improving crop productivity and resilience in arid and semi-arid areas, where drought represents a principal obstacle to agricultural output.

Electronic supplementary material

Below is the link to the electronic supplementary material.

12864_2024_11054_MOESM1_ESM.xlsx (11.2KB, xlsx)

Supplementary Material 1: Table S1 qRT-PCR primer sequences of genes.

12864_2024_11054_MOESM2_ESM.xlsx (11.2KB, xlsx)

Supplementary Material 2: Table S2 Summary of sequencing data of all samples.

12864_2024_11054_MOESM3_ESM.xlsx (875KB, xlsx)

Supplementary Material 3: Table S3 Differentially expressed genes (DEGs) in three subclusters.

12864_2024_11054_MOESM4_ESM.jpg (508.3KB, jpg)

Supplementary Material 4: Fig. S1 Overview of the gene expression profiles of different samples. (A) Pearson correlation coefficients (PCCs) of gene expression at different stages. CK, D, MD represent three treatments. (B) Principal component analysis results of genes at three treatments.

Acknowledgements

Not applicable.

Author contributions

ML, YZ, GT and AX contributed to conception and design of the study. JD, WL, ZW, ZC, and CW performed the experiments. JD, ZW, WL, and GT organized the database. JD, ZC and ZW wrote the paper. ML, YZ and AX revised the paper. All authors contributed to manuscript revision, read, and approved the submitted version.

Funding

This work was supported by the National Natural Science Foundation of China (32002027), the Natural Science Foundation of Sichuan Province (2022NSFSC1674), the earmarked fund for Sichuan Innovation Team Program of CARS (SCCXTD-2024-22), the seed industry revitalization project of Jiangsu province (JBGS2021-068).

Data availability

The datasets generated and/or analysed during the current study are available in the NCBI SRA repository (http://www.ncbi.nlm.nih.gov/bioproject/1124269).

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.

Contributor Information

Yangxia Zheng, Email: zhengyx13520@sicau.edu.cn.

Mengyao Li, Email: limy@sicau.edu.cn.

References

  • 1.Lesk C, Rowhani P, Ramankutty N. Influence of extreme weather disasters on global crop production. Nature. 2016;529(7584):84–7. [DOI] [PubMed] [Google Scholar]
  • 2.Zhang A, Liu M, Gu W, Chen Z, Gu Y, Pei L, Tian R. Effect of drought on photosynthesis, total antioxidant capacity, bioactive component accumulation, and the transcriptome of Atractylodes Lancea. BMC Plant Biol. 2021;21:293. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Seleiman MF, Al-Suhaibani N, Ali N, Akmal M, Alotaibi M, Refay Y, Dindaroglu T, Abdul-Wajid HH, Battaglia ML. Drought stress impacts on plants and different approaches to alleviate its adverse effects. Plants (Basel). 2021;10:259. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Hasanuzzaman M, Bhuyan M, Zulfiqar F, Raza A, Mohsin SM, Mahmud JA, Fujita M, Fotopoulos V. Reactive oxygen species and antioxidant defense in plants under Abiotic stress: revisiting the crucial role of a Universal Defense Regulator. Antioxidants. 2020;9:681. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Nahar K, Hasanuzzaman M, Alam MM, Fujita M. Glutathione-induced drought stress tolerance in mung bean: coordinated roles of the antioxidant defence and methylglyoxal detoxification systems. AoB Plants. 2015;7:plv069. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Chen K, Huang Y, Liu C, Liang Y, Li M. Transcriptome Profile Analysis of Arabidopsis reveals the Drought stress-Induced Long non-coding RNAs Associated with Photosynthesis, Chlorophyll synthesis, fatty acid synthesis and degradation. Front Plant Sci. 2021;12:643182. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7.Zhang H, Sun X, Dai M. Improving crop drought resistance with plant growth regulators and rhizobacteria: mechanisms, applications, and perspectives. Plant Commun. 2022;3:100228. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Reiter RJ, Rosales-Corral SA, Tan DX, Acuna-Castroviejo D, Qin LL, Yang SF, Xu KX. Melatonin, a full service anti-cancer agent: inhibition of initiation, progression and metastasis. Int J Mol Sci. 2017;18:843. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9.Xiao S, Liu LT, Wang H, Li DX, Bai ZY, Zhang YJ, Sun HC, Zhang K, Li CD. Exogenous melatonin accelerates seed germination in cotton (Gossypium hirsutum L). PLoS ONE. 2019; 14, e0216575. [DOI] [PMC free article] [PubMed]
  • 10.Erdal S. Melatonin promotes plant growth by maintaining integration and coordination between carbon and nitrogen metabolisms. Plant Cell Rep. 2019;38:1001–12. [DOI] [PubMed] [Google Scholar]
  • 11.Poeggeler B, Saarela S, Reiter RJ, Tan DX, Chen LD, Manchester LC, Barlow-Walden LR. Melatonin—A highly potent endogenous radical scavenger and electron donor: New aspects of the oxidation chemistry of this indole accessed in vitro. Ann N Y Acad Sci. 1994;738:419–20. [DOI] [PubMed] [Google Scholar]
  • 12.Bawa G, Feng LY, Shi JY, Chen GP, Cheng YJ, Luo J, Wu WS, Ngoke B, Cheng P, Tang ZQ. Evidence that melatonin promotes soybean seedlings growth from low-temperature stress by mediating plant mineral elements and genes involved in the antioxidant pathway. Funct Plant Biol. 2020;4:815–24. [DOI] [PubMed] [Google Scholar]
  • 13.Deng CC, Zhang JP, Huo YN, Xue HY, Wang W, Zhang JJ, Wang XZ. Melatonin alleviates the heat stress-induced impairment of sertoli cells by reprogramming glucose metabolism. J Pineal Res. 2022;73(3):e12819. [DOI] [PubMed] [Google Scholar]
  • 14.Fleta-Soriano E, Díaz L, Bonet E, Munné-Bosch S. Melatonin may exert a protective role against drought stress in maize. J Agron Crop Sci. 2017;302:286–94. [Google Scholar]
  • 15.Gao WY, Feng Z, Bai QQ, He JJ, Wang YJ. Melatonin-mediated regulation of growth and antioxidant capacity in salt-tolerant naked oat under salt stress. Int J Mol Sci. 2019;20:1176. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Amjadi Z, Namdjoyan S, Soorki AA. Exogenous melatonin and salicylic acid alleviates cadmium toxicity in safflower (Carthamus tinctorius L.) seedlings. Ecotoxicology. 2021;30:387–401. [DOI] [PubMed] [Google Scholar]
  • 17.Ren J, Yang X, Ma C, Wang Y, Zhao J. Melatonin enhances drought stress tolerance in maize through coordinated regulation of carbon and nitrogen assimilation. Plant Physiol Biochem. 2021;167:958–69. [DOI] [PubMed] [Google Scholar]
  • 18.Hu W, Zhang J, Wu Z, Loka DA, Zhao W, Chen B, Wang YH, Meng YL, Zhou ZG, Gao LG. Effects of single and combined exogenous application of abscisic acid and melatonin on cotton carbohydrate metabolism and yield under drought stress. Ind Crop Prod. 2022;176:114302. [Google Scholar]
  • 19.Cao L, Qin B, Zhang YX. Exogenous application of melatonin may contribute to enhancement of soybean drought tolerance via its effects on glucose metabolism. Biotechnol Biotec Eq. 2021;35:964–76. [Google Scholar]
  • 20.Jafari M, Shahsavar A. The effect of foliar application of melatonin on changes in secondary metabolite contents in two citrus species under drought stress conditions. Front. Plant Sci. 2021; 12. [DOI] [PMC free article] [PubMed]
  • 21.Deluc LG, Quilici DR, Decendit A, Grimplet J, Wheatley MD, Schlauch KA, Mérillon JM, Cushman JC, Cramer GR. Water deficit alters differentially metabolic pathways affecting important flavor and quality traits in grape berries of Cabernet Sauvignon and Chardonnay. BMC Genomics. 2009;10:212. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Li MY, Feng K, Hou XL, Jiang Q, Xu Z, Wang G, Liu J, Wang F, Xiong A. The genome sequence of celery (Apium graveolens L.), an important leaf vegetable crop rich in apigenin in the Apiaceae family. Hortic Res. 2020;7(1):1–10. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Du JG, Zhang HT, Li WL, Li XY, Wang Z, Zhang Y, Xiong AX, Li MY. Optimization of Protoplast Preparation System from leaves and Establishment of a transient Transformation System in Apium graveolens. Agronomy. 2023;13:2154. [Google Scholar]
  • 24.Liu JX, Feng K, Duan AQ, Li H, Yang QQ, Xu ZS, Xiong AS. Isolation, purification and characterization of an ascorbate peroxidase from celery and overexpression of the AgAPX1 gene enhanced ascorbate content and drought tolerance in Arabidopsis. BMC Plant Biol. 2019;19(1):488. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Duan AQ, Yang XL, Feng K, Liu JX, Xu ZS, Xiong AS. Genome-wide analysis of NAC transcription factors and their response to abiotic stress in celery (Apium graveolens L). Comput Biol Chem. 2020;84:107186. [DOI] [PubMed] [Google Scholar]
  • 26.Bates LS, Waldren RP, Teare ID. Rapid determination of free proline for water-stress studies. Plant Soil. 1973;39:205–7. [Google Scholar]
  • 27.Lu X, Min W, Shi Y, Tian L, Li P, Ma T, Zhang Y, Luo C. Exogenous melatonin alleviates alkaline stress by removing reactive oxygen species and promoting antioxidant defence in Rice Seedlings. Front Plant Sci. 2022;13:849553. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Arnon DI. Copper enzymes in isolated chloroplasts. Polyphenoloxidase in Beta vulgaris. Plant Physiol. 1949;24:1–15. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Liu J, Wang W, Wang L, Sun Y. Exogenous melatonin improves seedling health index and drought tolerance in tomato. Plant Growth Regul. 2015;77:317–26. [Google Scholar]
  • 30.Ruan Q, Bai X, Wang Y. Regulation of endogenous hormone and miRNA in leaves of alfalfa (Medicago sativa L.) seedlings under drought stress by endogenous nitric oxide. BMC Genomics. 2024;25:229. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.Reiter RJ, Mayo C, Tan DX, Sainz R, Alatorre-Jimenez M, Qin L. Melatonin as an antioxidant: under promises but over delivers. J Pineal Res. 2016;61:253–78. [DOI] [PubMed] [Google Scholar]
  • 32.Su X, Fan X, Shao R, Guo J, Wang Y, Yang J, Yang Q, Guo L. Physiological and iTRAQ-based proteomic analyses reveal that melatonin alleviates oxidative damage in maize leaves exposed to drought stress. Plant Physiol Biochem. 2019;142:263–74. [DOI] [PubMed] [Google Scholar]
  • 33.Cui G, Zhao X, Liu S, Sun F, Zhang C, Xi Y. Beneficial effects of melatonin in overcoming drought stress in wheat seedlings. Plant Physiol Biochem. 2017;118:138–49. [DOI] [PubMed] [Google Scholar]
  • 34.Li Z, Su X, Chen Y, Fan X, He L, Guo J, Wang Y, Yang Q. Melatonin improves drought resistance in maize seedlings by enhancing the antioxidant system and regulating abscisic acid metabolism to maintain stomatal opening under peginduced drought. J Plant Biol. 2021;64:1–14. [Google Scholar]
  • 35.Zhao PX, Miao ZQ, Zhang J, Chen SY, Liu QQ, Xiang CB. Arabidopsis MADS-box factor AGL16 negatively regulates drought resistance via stomatal density and stomatal movement. J Exp Bot. 2020;71(19):6092–106. [DOI] [PubMed] [Google Scholar]
  • 36.Huang B, Chen YE, Zhao YQ, Ding CB, Liao JQ, Hu C, Zhou LJ, Zhang ZW, Yuan S, Yuan M. Exogenous melatonin alleviates oxidative damages and protects photosystem II in maize seedlings under drought stress. Front Plant Sci. 2019;10:677. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 37.Zhou R, Kan X, Chen J, Hua H, Li Y, Ren J, Feng K, Liu H, Deng D, Yin Z. Drought-induced changes in photosynthetic electron transport in maize probed by prompt fluorescence, delayed fluorescence, P700 and cyclic electron flow signals. Environ Exp Bot. 2019;158:51–62. [Google Scholar]
  • 38.Lv Y, Li Y, Liu X, Xu K. Photochemistry and proteomics of ginger (Zingiber officinale Roscoe) under drought and shading. Plant Physiol Biochem. 2020;151:188–96. [DOI] [PubMed] [Google Scholar]
  • 39.Zhang Z, Cao B, Gao S, Xu K. Grafting improves tomato drought tolerance through enhancing photosynthetic capacity and reducing ROS accumulation. Protoplasma. 2019;256:1013–24. [DOI] [PubMed] [Google Scholar]
  • 40.Li S, Tian Y, Wu K, Ye Y, Yu J, Zhang J, Liu Q, Hu M, Li H, Tong Y, Harberd N, Fu X. Modulating plant growth–metabolism coordination for sustainable agriculture. Nature. 2018;560:595–600. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41.Li X, Zhang W, Niu D, Liu X. Effects of abiotic stress on chlorophyll metabolism. Plant Sci. 2024;342:112030. [DOI] [PubMed] [Google Scholar]
  • 42.Babbar R, Karpinska B, Grover A, Foyer CH. Heat-induced oxidation of the nuclei and cytosol. Front. Plant Sci. 2021;11:617779. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 43.Martinez V, Nieves-Cordones M, Lopez-Delacalle M, Rodenas R, Mestre TC, Garcia-Sanchez F, Rubio F, Nortes PA, Mittler R, Rivero RM. Tolerance to stress combination in tomato plants: new insights in the protective role of melatonin. Molecules. 2018;23:535. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 44.Shanga FZ, Liu RL, Wu WJ, Han YC, Fang XJ, Chen HJ, Haiyan Gao HY. Effects of melatonin on the components, quality and antioxidant activities of blueberry fruits. LWT. 2021;147:111582. [Google Scholar]
  • 45.Li M, Zhou J, Du J, Li X, Sun Y, Wang Z, Lin Y, Zhang Y, Wang Y, He W, Wang X, Chen Q, Zhang Y, Luo Y, Tang H. Comparative physiological and transcriptomic analyses of improved heat stress tolerance in celery (Apium graveolens L.) caused by Exogenous Melatonin. Int J Mol Sci. 2022;23(19):11382. [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

12864_2024_11054_MOESM1_ESM.xlsx (11.2KB, xlsx)

Supplementary Material 1: Table S1 qRT-PCR primer sequences of genes.

12864_2024_11054_MOESM2_ESM.xlsx (11.2KB, xlsx)

Supplementary Material 2: Table S2 Summary of sequencing data of all samples.

12864_2024_11054_MOESM3_ESM.xlsx (875KB, xlsx)

Supplementary Material 3: Table S3 Differentially expressed genes (DEGs) in three subclusters.

12864_2024_11054_MOESM4_ESM.jpg (508.3KB, jpg)

Supplementary Material 4: Fig. S1 Overview of the gene expression profiles of different samples. (A) Pearson correlation coefficients (PCCs) of gene expression at different stages. CK, D, MD represent three treatments. (B) Principal component analysis results of genes at three treatments.

Data Availability Statement

The datasets generated and/or analysed during the current study are available in the NCBI SRA repository (http://www.ncbi.nlm.nih.gov/bioproject/1124269).

Articles from BMC Genomics are provided here courtesy of BMC

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