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.

长期干旱胁迫对大豆生长产生不可逆转的影响，并降低了产量。褪黑素可以减轻干旱胁迫对生长的抑制和植物的损害。在这项研究中，我们调查了叶面褪黑素对干旱胁迫下开花期大豆的生理，代谢组生长和产量的影响。外源性褪黑素增加了干旱胁迫期间抗氧化酶的活性，并降低了活性氧的产生和膜脂质过氧化作用。褪黑素还减轻了干旱胁迫下较低的光合作用能力，并调节了碳和氮的同化作用以及内源激素的含量。使用UPLC-MS / MS代谢组学检测平台共检测到518种代谢物。干旱胁迫减少了糖，氨基酸，有机酸和核苷酸，并增加了类黄酮和酚酸的含量。与干旱胁迫相比，褪黑素减少了类黄酮和酚酸的含量，并增加了氨基酸及其衍生物（L-天冬酰胺，L-（-）-酪氨酸，L-苯丙氨酸，DL-高半胱氨酸，L-蛋氨酸，3， （4-二羟基和DL-苯丙氨酸），黄素腺嘌呤二核苷酸（FAD），6'-顺式肉桂酰基8-表锡二酸，5-氨基环庚烷-1,2,3-三醇和5,8,11,14-十五碳酰胺。此外，褪黑素减轻了干旱胁迫引起的生长和产量下降。我们的研究表明，外源褪黑素改善了大豆的抗氧化系统和光合作用能力，改变了碳和氮的代谢，促进了氨基酸及其衍生物的积累，减少干旱胁迫下植物的生长抑制和产量损失。因此，叶面褪黑素在农业中具有重要的潜力。