Table 1.
Effects of ALA priming on the tolerance to environmental stressors.
| Type of Stress | Plant Species | Stress Concentration | Mode of ALA Application and ALA Level | Effects | References |
|---|---|---|---|---|---|
| Salt stress | Asparagus (Asparagus aethiopicus L.) | 2000 and 4000 ppm NaCl | Foliar application of 3, 5, and 10 ppm | An increase in plant biomass, leaf antioxidant activity, phenolic content, proline accumulation, and photosynthetic rate | Al-Ghamdi et al., 2018 |
| Barley (Hordeum vulgare L.) | 150 mM NaCl | Hydroponics of 10, 30, and 60 mg/L | Proline content increased and ROS content decreased | Averina et al., 2010 | |
| 100 mM NaCl | Foliar application of 7 ppm | Increased chlorophyll content, antioxidant enzyme activity, and stress responsive gene expression | El-Esawi et al., 2018 | ||
| Cassia seed (Cassia obtusifolia L.) | 100 mM NaCl | Seed soaking of 5, 10, 15, and 20 mg/L; root irrigation of 10, 25, 50, and 100 mg/L | Significantly increased chlorophyll content, total soluble sugars, free proline, and soluble protein content; increased photosynthesis and antioxidant enzyme activities | Zhang et al., 2013 | |
| Cucumber (Cucumis sativus L.) | 75 mM NaCl | Foliar application of 50 mg/L | ALA might delay and counteract the upregulated expression of cucumber PIP aquaporin gene (CsPIP1:1) and cucumber NIP aquaporin gene (CsNIP) genes in cucumber seedlings under NACL stress | Yan et al., 2014 | |
| 50 mM NaCl | Foliar application of 25 mg/L | Enhancement of ascorbate-glutathione cycle; increase in shoot and root growth | Wu et al., 2019 | ||
| 50 mM NaCl | Foliar application of 25 mg/L | Increased ROS production in roots, resulting in upregulation of ion trans-porters SOS1, NHX1, and HKT1 | Baral, 2019 | ||
| 50 mM NaCl | Foliar application of 25 mg/L | Improved plant growth; upregulation of Na+/H+ antiporter SOS1 and NHX1 at the plasma and vesicle membranes, thereby reducing ion toxicity | Wu et al., 2021 | ||
| 50 mM NaCl | Foliar application of 25 mg/L | Downregulation of ferrochelatase (HEMH) gene expression; increased in chlorophyll biosynthesis pathway | Wu et al., 2018 | ||
| Date Palm (Phoenix dactylifera L.) | Seawater treatments at 1, 15, and 30 mS cm–1 | Root irrigation of 0.08% ALA based fertilizer (PentaKeep-V) | Enhanced photosynthetic assimilation by increasing chlorophyll content and stomatal conductance | Tarek et al., 2007 | |
| Maize (Zea mays L.) | 100 mM NaCl | Foliar application and seed soaking of 20 mg/L | Improved plant growth; activated the synthesis and accumulation of endogenous NO, thereby increasing the antioxidant capacity of plants | Kaya et al., 2020 | |
| Oilseed rape (Brassica napus L.) | 100 and 200 mM NaCl | Foliar application of 30 mg/L | Increased plant growth and chloroplast photosynthetic efficiency; reduced Na+ uptake and oxidative stress | Naeem et al., 2012 | |
| 200 mM NaCl | Foliar application of 30 mg/L | Increased aboveground biomass and net photosynthetic rate; promoted chlorophyll accumulation by promoting increased intermediate levels of the tetrapyrrole synthesis pathway; upregulated the expression of genes P5CS and ProDH encoding proline metabolic enzymes | Xiong et al., 2018 | ||
| 100 and 200 mM NaCl | Foliar application of 30 mg/L | Improved root and shoot growth; Enhanced plant photosynthesis, chlorophyll content; regulated the uptake of Na+ and leaf water potential | Naeem et al., 2010 | ||
| Peach (Prunnus persica L.) | 100 mM NaCl | Foliar application of 200 mg/L | Exogenous ALA treatment could improve the growth and relieve the NACL stress injury of peach seedlings by increasing photochemical efficiency, osmotic content, and antioxidant enzyme activity | Ye et al., 2016 | |
| Radix Isatidis (Isatis indigotica Fort.) | 100 mM NaCl | Foliar application of 12.5, 16.7, 25.0, and 50.0 mg/L | Increased antioxidant enzyme activity, chlorophyll content, and net photo-synthetic rate | Tang et al., 2017 | |
| Sunflower (Helianthus annuus L.) | 150 mM NaCl | Foliar application of 20, 50, and 80 mg/L | Decreased leaf H2O2 content and increased SOD activity | Akram et al., 2012 | |
| Swiss chard (Beta vulgaris L.) | 40 and 80 mM saline (molar ratio NaCl/Na2SO4 = 9:1) | Foliar application of 60 and 120 μM | The ionic toxicity was reduced by decreasing the Na+ content and Na+/K+ ratio; increased the total nitrogen and GB content | Liu et al., 2014 | |
| Watermelon (Citrullus lanatus L.) | 100 mM NaCl | Foliar application of 1.25 mM | Regulated nitrogen metabolism, reduced ion toxicity caused by salt stress, and increased soluble protein and proline | Chen et al., 2017 | |
| Extreme Temperature | Cucumber (Cucumis sativus L.) | 42/38 °C (day/night) | Foliar application of 3 μM | Reduced ROS content and growth inhibition under heat stress; enhanced antioxidant enzyme (SOD, CAT, and GPX) activity and proline content | Zhang et al., 2012 |
| 12 °C/8 °C (day/night) | Foliar application of 15, 30, and 45 mg/L ALA | Nutrient contents (N, P, K, Mg, Ca, Cu, Fe, Mn, and Zn) and endogenous hormones (JA, IAA, BR, IPA, and ZR) were enhanced in roots and leaves; Increased chlorophyll content, photosynthetic capacity, and antioxidant enzymes (SOD, POD, CAT, APX, and GR); reduced growth inhibition of seedlings by cold stress | Anwar et al., 2018 | ||
| 16 °C/8 °C (day/night) | Add to the culture substrate of 10, 20, or 30 mg ALA·kg−1 (ALA were mixed with a constant weight of substrate (kg)) | Significantly reduced plant growth inhibition; increased chlorophyll content, antioxidant enzymes (SOD, CAT, and POD) activity; reduced accumulation of ROS and malondialdehyde in roots and leaves | Anwar et al., 2020 | ||
| Drooping wild ryegrass (Elymus nutans Griseb.) | 5 °C | Seed soaking of 0.1, 0.5, 1, 5, 10, and 25 mg/L | Significantly increased seed respiration rate and ATP synthesis and protected germinating seeds from cold stress; increased GSH, AsA, total glutathione, and total ascorbate concentrations, as well as SOD, CAT, APX, and GR activities | Fu et al., 2014 | |
| 5 °C | Foliar application of 0.5, 1, 5, 10, and 26 mg/L | NO might be a downstream signal that mediates ALA-induced cold tolerance, thereby enhancing antioxidant defense | Fu et al., 2015 | ||
| 5 °C | Root soaking of 0.5, 1, 5, 10, and 26 mg/L | NO might act as a downstream signal to mediate ALA-induced cold resistance by activating antioxidant defense and PM H+-ATPase and maintaining Na+ and K+ homeostasis | Fu et al., 2016 | ||
| Maize (Zea mays L.) | 14 °C/5 °C (day/night) | Foliar application of 0.15 mM | Increased proline accumulation, antioxidant enzymes (SOD and CAT) and RuBP carboxylase activity; prevented reductions in maize crop yield due to low-temperature stress | Wang et al., 2018 | |
| Red pepper (Capsicum annuum cv. Sena) | 4 °C | Seed soaking of 1, 10, 25, 50, and 100 ppm | Resulted in higher germination and seedling emergence percentages, as well as faster germination and seedling emergence | Korkmaz et al., 2009 | |
| 3 °C | Seed soaking, foliar spray and soil drench of 1, 10, 25, 50, and 100 ppm | Improved plant quality, chlorophyll content, sucrose, and proline content; enhanced SOD activity | Korkmaz et al., 2010 | ||
| Rice (Oryza sativa L.) | 3 °C, 5 °C | Root soaking of 0.001, 0.1, 1, and 5 ppm | Reduced cold injury-induced tissue electrolyte leakage | Hotta et al., 1998 | |
| 10 °C | Seed soaking of 8.5 mM | Increased antioxidant enzymes (SOD, POD, APX, and GPX) activity; increased relative gene expression of enzymes of PA biosynthesis | Sheteiwy et al., 2017 | ||
| Soybean (Glycine max L.) | 4 °C | Hydroponics of 5, 10, 15, 20, 30, and 40 μM | Increased chlorophyll content and relative water content of leaves; enhanced activity of antioxidant enzymes CAT and HO-1 | Balestrasse et al., 2010 | |
| Tomato (Solanum lycopersicum) | 15 °C/8 °C (day/night) | Foliar application of 5, 10, 25, 50, and 100 mg/L | ALA induced H2O2, which in turn increased the ratio of GSH and ASA, leading to enhanced antioxidant capacity; significantly increased the activities of SOD, CAT, APX, DHAR, and GSH | Liu et al., 2018 | |
| 15 °C/8 °C (day/night) |
Foliar application of 5, 10, 25, 50, and 100 mg/L | ALA pretreatment-induced CAT and ASA-GSH reliably eliminated excess ROS under low temperature stress and maintained redox homeostasis | Liu et al., 2018 | ||
| 15 °C/8 °C (day/night) |
Foliar application of 25 mg/L | ALA triggered NO production directly, or induced H2O2 and JA signals to trigger NO production, thus NO interacted with JA to regulate cold-induced oxidative stress | Liu et al., 2019 | ||
| Drought stress | Kentucky bluegrass (Poa pratensis L.) | 10% PEG 6000 | Foliar application of 10 mg/L | Improved turf quality and leaf relative water content; enhanced antioxidant enzymes (SOD, CAT, APX, GPX, DHAR, and GR), ASA, and GSH content, thus reducing oxidative damage | Niu et al., 2017 |
| Oilseed rape (Brassica napus L.) | Drought stress (40% of water-holding capacity) | Foliar application of 30 mg/L | Maintained relatively higher leaf water status; enhanced chlorophyll content and net photosynthetic rate; increased antioxidant enzyme (POD and CAT) activity | Liu et al., 2013 | |
| Drought stress (40% of water-holding capacity) | Foliar application of 30 mg/L | Expression of photosynthetic genes (RBCS, TPI, FBP, FBPA, and TKL) was upregulated; increased leaf hexose and sucrose accumulation and maintenance of starch content | Liu et al., 2016 | ||
| Sunflower (Helianthus annuus L.) | Water stress (70% field capacity) | Foliar application of 10, 20, and 30 mg/L | Reduced oxidative damage by lowering H2O2 and MDA contents | Rasheed et al., 2020 | |
| Drought stress (40% of water-holding capacity) | Foliar application of 25, 50, 75, and 100 mg/L | Enhancement of stay green and CAT, SOD, and APX activities, thus reducing drought-induced yield losses and improving oil contents | Sher et al., 2021 | ||
| Wheat (Triticum aestivum L.) | Irrigation interval of 7, 14, and 21 days | Foliar application of 25, 50, and 100 ppm | Increased grain yield | Al-Thabet et al., 2006 | |
| Water deficit (60% and 80% of field capacity) | Foliar application of 50, 100, and 150 mg/L | Improved leaf fluorescence (qN, NPQ, and Fv/Fm), shoot and root K+, root Ca2+, proline, and GB accumulation | Akram et al., 2018 | ||
| Water stress (30% maximum water capacity) | Foliar application of 30 mg/L | Increased plant growth, photosynthesis, and chlorophyll content; reduced the degree of damage to cell membranes during early nutritional development | Ostrowska et al., 2019 | ||
| 80% (mild drought stress), and 60% (high drought stress) | Foliar application of 50, 100, and 150 mg/L | Increased fresh and dry weight of shoots and roots, chlorophyll content, GB content, and N content in leaves and roots | Kosar et al., 2015 | ||
| UV-B stress | lettuce (Lactuca sativa L.) | 3.3 W m−2 UV-B | Foliar application of 10 and 25 ppm | ALA treatment resulted in a substantial increase in phenylalanine ammonia lyase (PAL) and γ-tocopherol methyltransferase (γ-TMT) gene expression, antioxidant enzyme activity, and chlorophyll a and b concentrations. | Aksakal et al., 2017 |
| Pigeon pea (Cajanus cajan L.) | enhanced UV-B (2.2 kJ m−2d−1) | Seed soaking of 25 and 100 μM | Reduced germination time and increased germination index; upregulated photosynthesis, antioxidant enzymes (CAT, SOD, and POD), total phenolic content, and total flavonoid content to balance ROS and reduce UV-B damage to plant productivity | Gupta et al., 2021 | |
| enhanced UV-B (2.2 kJ m−2d−1) | Seed soaking of 25 and 100 μM | Increased plant growth and growth regulating parameters; increased enzyme activity and non-enzymatic antioxidant content in the plant defense system and reduced oxidative stress in seedlings | Gupta et al., 2021 |
The optimum levels of ALA are shown in bold.