Melatonin-Mediated Modulation of Grapevine Resistance Physiology, Endogenous Hormonal Dynamics, and Fruit Quality Under Varying Irrigation Amounts.

Grapevine, as a globally significant economic fruit tree, is highly sensitive to water stress, which not only damages its growth but also affects the formation of fruit quality. Melatonin (MT), acting as a signaling molecule, plays a crucial role in plant stress responses. However, the regulatory mechanisms of MT on grape leaf physiological characteristics and fruit quality under different irrigation amounts have not been fully elucidated. In this experiment, grape leaves were treated with a 150 μmol·L MT solution at 0, 30, 60, and 90 days after flowering under different irrigation amounts (360, 300, 240, and 180 mm). It was found that MT significantly increased the contents of osmotic adjustment substances in leaves, reduced the level of reactive oxygen species, enhanced the activity of antioxidant enzymes, and promoted the metabolism of the ascorbic acid-glutathione cycle, thereby improving the antioxidant capacity of grapes and effectively alleviating the damage caused by a water deficit. At the same time, MT also maintains the dynamic balance of endogenous hormones by upregulating and downregulating the expression levels of related genes, thereby improving fruit quality. In summary, this study reveals the potential application value of MT in enhancing the drought resistance and fruit quality of grapes.