Physiological and UPLC-MS/MS widely targeted metabolites mechanisms of alleviation of drought stress-induced soybean growth inhibition by melatonin

Long-term drought stress has irreversible effects on soybean growth and reduces yield. Melatonin can alleviate the growth inhibition and plant damage resulting from drought stress. In this study, we investigated the effects of foliar melatonin application on the physiology, metabolome growth and yield of flowering stage soybeans during drought stress. Exogenous melatonin increased the activity of antioxidant enzymes during drought stress and decreased the production of reactive oxygen species and membrane lipid peroxidation. Melatonin also mitigated lower photosynthesis ability during drought stress, and regulated carbon and nitrogen assimilation and the endogenous hormone content. A total of 518 metabolites were detected using the UPLC-MS/MS metabolome detection platform. Drought stress reduced the accumulation of sugars, amino acids, organic acid, and nucleotides, and increased the content of flavonoid and phenolic acid. Compare with drought stress treatment, melatonin reduced the content of flavonoid and phenolic acid, and increased amino acids and their derivatives (L-asparagine, L-(-)-tyrosine, L-phenylalanine, DL-homocysteine, L-methionine, 3,4-Dihydroxy, and DL-phenylalanine), flavin adenine dinucleotide (FAD), 6′-cis-cinnamoyl 8-epikingisidic acid, 5-aminocycloheptane-1,2,3-triol and 5,8,11,14-pentadecanoamide. Moreover, melatonin alleviated growth and yield declines caused by drought stress. Our study showed that exogenous melatonin improved the soybean antioxidant system and photosynthesis capacity, altering carbon and nitrogen metabolism, promoted the accumulation of amino acids and their derivatives, reducing plant growth inhibition and yield loss during drought stress. Therefore, the foliar application of melatonin has important potential in agriculture.