Table 1.
Roles of melatonin in drought stress tolerance.
| Common Name | Scientific Name | Drought Treatment | Melatonin Treatment | Effects | Reference | |
|---|---|---|---|---|---|---|
| Concentration* | Application Form | |||||
| Model Plants | ||||||
| Arabidopsis | Arabidopsis thaliana | Water withholding (21 d) | 50 µM | Supplemented with nutrient solution | Stress-responsive genes ▲, soluble sugars ▲ | [40] |
| Field Crops | ||||||
| Rice | Oryza sativa | Water drainage from vessels (5 d) | 100 μM | Pretreatment in growing distilled water | Plant growth ▲, osmoprotectants proline ▲, stress-responsive genes ▲, mitochondrial structure ▲, ROS ▼, electroleakage ▼ | [41] |
| Maize | Zea mays | Water withholding (8 d), melatonin application during recovery, followed by withholding (8 d). | 1 mM | Supplemented with irrigation | Photoprotection (PSII efficiency) ▲ | [34] |
| Maize | Z. mays | 30–60% SWC (8d) | 100 µM | Foliar application | Recovering after rehydration ▲, photosynthesis ▲, stomatal conductance ▲, transpiration rates ▲, cell turgor and water holding capacity ▲, enzymatic and nonenzymatic antioxidants ▲, osmotic potential ▼, ROS ▼ | [42] |
| Maize | Z. mays | 20% PEG6000(3 d) | 10–100 μM | Foliar application pre-treatment | Photosynthesis ▲, antioxidant enzymes ▲, carbon fixation ▲, amino acids and secondary metabolites biosynthesis ▲, ROS ▼ | [26] |
| Maize | Z. mays | Water withholding (7 d) | 100 µM | Two methods (root-irrigation and foliar application) | Photosynthesis ▲, ROS ▼ | [43] |
| Maize | Z. mays | 40–45% field capacity (50 d) | 50 µM (foliar spray) and 100 µM (soil drench) | Foliar application or soil treatment | Photosynthesis ▲, antioxidant enzymes ▲, ROS ▼ | [44] |
| Wheat | Triticum aestivum | 40% and 60% field capacity (7 d) | 500 µM | Soil application | Chloroplast structure▲, photosynthesis ▲, cell turgor and water holding capacity ▲, GSH and AsA contents ▲, antioxidant enzymes▲, GSH–AsA cycle-related genes ▲, ROS ▼, membrane damage ▼ | [45] |
| Wheat | T. aestivum | 30% pot holding capacity (8 d) | 100 µM | Soil application | Recovering after rehydration ▲, biomass and root/shoot ratio ▲, water holding capacity ▲, chlorophyll ▲, photosynthesis ▲, ROS ▼, MDA ▼ | [46] |
| Wheat | T. aestivum | 20% PEG 6000 (7 d) | 10 and 100 μM (variety-dependent) | Seeds treatment | Germination percentage ▲, germination index ▲, germination potential ▲, radicle length and number ▲, plumule length ▲, lysine (germination-related amino acid) ▲ | [47] |
| Tartary Buckwheat | Fagopyrum tataricum | 20% field capacity (15 d) | 100 μM | Foliar application | Water status ▲, osmoprotection ▲, secondary metabolites▲, antioxidant enzymes▲, photosynthesis ▲, ROS ▼ | [48] |
| Barley | Hordeum vulgare | (Combined drought and cold) | 1 mM | Foliar or soil application | Endogenous melatonin▲, ABA ▲, water status ▲, antioxidants ▲, photosynthesis ▲, PSII efficiency ▲ | [49] |
| Soybean | Glycine max | 20% field capacity (10 d) | 50 µM | Seed coating | Seedlings growth ▲, biomass ▲, electrolyte leakage ▼ | [36] |
| Soybean | G. max | 15% PEG 6000 (7 d) | 100 µM | Supplemented with nutrient solution | Seedlings growth ▲, photosynthesis ▲ | [38] |
| Soybean | G. max | 45% RSWC (15 d) | 100 µM | Foliar application | Antioxidant enzymes ▲, osmolytes ▲, MDA ▼ | [25] |
| Soybean | G. max | 15% PEG6000 (3 d) | 100 μM | Foliar and root application | Plant growth and flowering ▲, seed yield ▲, gas exchange▲, PSII efficiency ▲, antioxidant enzymes ▲, MDA ▼ | [50] |
| Cassava | Manihot esculenta | 20% PEG 6000 (11 d) | 100 µM | Soil application | POD activity▲, ROS ▼ | [37] |
| Cotton | Gossypium hirsutum | 10% PEG 6000 (7 d) | 100 µM | Seeds pre-soaking | Number and opening of stomata in cotton testa ▲, germination parameters▲, antioxidant enzymes ▲, osmoprotection ▲, GA3 ▲, ABA ▼, ROS ▼, MDA ▼ | [51] |
| Alfalfa | Medicago sativa | Water withholding (7 d) | 10 µM | Soil application | Chlorophyll ▲, stomatal conductance ▲, osmoprotection ▲, Nitro-oxidative homeostasis ▲, cellular redox disruption ▼,MDA ▼, ROS ▼ | [52] |
| Fruits | ||||||
| Apple | Malus spp. | Water withholding (6 d) | 100 µM | Soil application | Water holding capacity ▲, chlorophyll ▲, photosynthesis ▲, antioxidants ▲, stomatal opening regulation ▲, melatonin biosynthesis genes ▲, electrolyte leakage ▼, ROS▼, ABA ▼ through ABA synthesis gene▼ and catabolic genes ▲ | [53] |
| Apple | M. domestica | 50% field capacity (3 months with sampling every month) | 100 µM | Soil application | Plant growth ▲, nutrients uptake fluxes ▲, N metabolism ▲, endogenous melatonin ▲, chlorophyll ▲, photosynthesis ▲, relative water content ▲, stomatal status ▲, electrolyte leakage ▼, ROS ▼ | [54] |
| Apple | M. domestica | 50% field capacity (3 months with sampling every month) | 100 µM | Soil application | Chlorophyll ▲, photosynthesis ▲, photoprotection ▲, antioxidant enzymes ▲, GSH and AsA contents ▲, oxidative damage ▼, leaf senescence ▼, senescence-associated gene 12 ▼, pheophorbide a oxygenase-related gene ▼, ROS▼ | [55] |
| Grape | Vitis vinifer | 10% PEG 6000 (12 d) | 50, 100 and 200 nM | Roots pretreatment | Photoprotection ▲, leaf thickness ▲, spongy tissue ▲, stoma size ▲, chloroplast structure ▲, enzymatic and nonenzymatic antioxidants ▲, osmoprotectants (free proline) ▲, ultrastructural damage ▼, oxidative injury ▼ | [33] |
| Grapevine | V. amurensis V. vinifera and V. labruscana | 10% PEG 6000 (4 d) | Endophyte colonization of secreted-melatonin bacteria | Bacillus amyloliquefaciens SB-9 colonization | Melatonin synthesis and its intermediates ▲, plant growth ▲, ROS ▼, MDA ▼ | [56] |
| Grape | V. vinifer | Water withholding (18 d) | 100 μM | Supplemented with irrigation | MDA ▼, relative conductivity ▼ | [57] |
| Grape | V. vinifer | Water withholding (18 d) | 100 μM | Supplemented with irrigation | Chlorophyll ▲, SOD activity ▲ | [28] |
| Kiwifruit | Actinidia. chinensis var. deliciosa | Water withholding (9 d) (RWC below 35% field capacity) | 100 μM | Supplemented with irrigation | Root vigor ▲, osmoprotectants ▲, proteins biosynthesis ▲, chlorophyll ▲, photosynthesis ▲, light energy absorption ▲, photoprotection ▲, CO2 fixation-associated genes ▲, MDA ▼, cell membranes damage ▼, stomatal closure ▼ | [58] |
| Kiwifruit | A. chinesis | water withholding (9 days) | 100 µM | Irrigation pretreatment | Water holding capacity ▲, antioxidant enzymes-related genes ▲, GSH–AsA cycle-related genes ▲, ROS ▼, MDA ▼ | [27] |
| Chinese hickory | Carya cathayensis | 30% PEG 6000 (10–40 d) | 100 µM | Foliar application pretreatment | Recovering after rehydration ▲, photosynthesis ▲, antioxidants ▲, osmoprotectants ▲, metabolic pathways-related genes ▲, antioxidant enzymes-related genes ▲, ROS ▼ | [59] |
| Vegetables | ||||||
| Tomato | Solanum lycopersicum | Water withholding for (5–20 d after moderate drought) | 0.1 mM | Supplemented with irrigation | Photosynthesis ▲, root vigor ▲, PSII efficiency ▲, antioxidants ▲, toxic substances ▼ | [60] |
| Tomato | S. lycopersicum | 10% PEG (7 d) | 200 µM | Foliar application | Chlorophyll ▲, p-coumaric acid content ▲, antioxidant enzymes ▲, MDA ▼ | [29] |
| Pepper | Capsicum annuum | 10% PEG (8 d) | 50 µM | Seed pretreatment | Water holding capacity ▲, endogenous melatonin ▲, GSH content ▲, chlorophyll ▲, carotenoids ▲, proline ▲, antioxidant enzymes ▲, MDA ▼ | [30] |
| Watermelon | Citrullus lanatus | Water withholding (4 d) | 150 µM | Root pretreatment | Wax accumulation ▲, melatonin–ABA crosstalk ▲ | [39] |
| Cucumber | Cucumis sativus | 18% PEG 6000 (days) | 100 µM | Seeds priming and nutrient solution | Seed germination ▲, root growth ▲, root/shoot ratio ▲, roots vigor ▲, chlorophyll ▲, photosynthesis ▲, chloroplasts ultrastructure ▲, antioxidant enzymes ▲, ROS ▼ | [61] |
| Rapeseed | Brassica napus | 4% PEG 6000 (7 d) | 0.05 mM | In PEG solution | Plant growth ▲, antioxidants ▲, osmoprotectants ▲, ROS ▼ | [62] |
| Rapeseed | B. napus | −0.3 and −0.4 Mpa PEG 6000 (7 d) | 500 µM | Seed priming | Chlorophyll ▲, stomatal regulation ▲, chloroplast structure ▲, cell expansion and cell wall ▲, antioxidant enzymes ▲, osmoprotectants ▲, oxidative injury ▼ | [35] |
| Ornamental and Medicinal Plants | ||||||
| Jinyu Chuju | Dendranthma morifolium | 40% field capacity (6 d) | 100 µM | Foliar application | Chlorophyll ▲, photosynthesis ▲, biomass ▲, osmoprotectants (TSS and proline) ▲, cell membrane damage ▼, relative conductivity ▼, MDA ▼ | [63] |
| Moldavian balm (Dragon head) | Dracocephalum moldavica | 40–60% field capacity | 100 µM | Foliar application | Plant growth and flowering ▲, antioxidants ▲, chlorophyll ▲, water holding capacity ▲, ROS ▼, MDA ▼ | [64] |
| Creeping bentgrass | Agrostisstolonifera | Water withholding (14 d) | 20 μM | Foliar application | Visual quality ▲, PSII efficiency ▲, chlorophyll ▲, water holding capacity ▲, melatonin biosynthesis genes ▲, dehydration responsive genes ▲, Chlorophyll-degradation genes ▼, leaf senescence ▼, ROS ▼, MDA ▼ | [65] |
| Tall fescue | Festuca arundinacea | Water withholding (10 d) | 20 μM | Irrigation pretreatment | Plant growth ▲, chlorophyll ▲, antioxidant enzymes ▲, ROS ▼, MDA ▼ | [66] |
| Bermudagrass | Cynodon dactylon | Withholding water (21 d) | 20 and 100 μM | Irrigation pretreatment | Plant growth ▲, chlorophyll ▲, survival rate ▲, antioxidant enzymes ▲, stress-responsive genes ▲, metabolic regulation ▲, hormonal signaling-related genes regulation ▲, ROS ▼ | [67] |
| Fenugreek | Trigonella foenum-graecum | 19.5% PEG 6000(21 d) | 100 and 300 μM | Foliar application pre-treatment | Endogenous melatonin and secondary metabolites ▲, chlorophyll ▲, antioxidant enzymes ▲, ROS ▼ | [68] |
| Coffee | Coffea arabica | 40% of max moisture retention capacity (21 d) | 300 μM | Soil application | Root vigor ▲, photoprotection ▲, gas exchange ▲, carboxylation efficiency ▲, chlorophyll ▲, antioxidants ▲, MDA ▼ | [31] |
| Tea | Camellia sinensis | 20% PEG 6000 (2 d) | 100 µM | Foliar application pre-treatment | Photosynthesis ▲, GSH and AsA contents ▲, antioxidant enzymes ▲, antioxidant enzymes-related genes ▲, ROS ▼, MDA ▼ | [32] |
| Other Crops | ||||||
| Tobacco, Tomato and Cucumber | Nicotiana benthamiana, S. lycopersicum and C. sativus | Water withholding (6 d) | 10 μM | Foliar application | MDA ▼, drought tolerance ▲ | [23] |
▲ or ▼, enhanced or decreased compared to control. ROS, reactive oxygen species; PSII, photosystem II; GSH, glutathione; AsA, ascorbate; MDA, malondialdehyde; ABA, abscisic acid; GA3, gibberellic acid; SOD, superoxide dismutase; POD, peroxidase; TSS, total soluble sugar. * Only those doses of exogenous melatonin that had a superior positive impact on plant tolerance against drought stress have been selected.