Melatonin application improves berry coloration, sucrose synthesis, and nutrient absorption in 'Summer Black' grape

In this study, we investigated the effects of melatonin application on berry coloration, sugar accumulation, and nutrient absorption in 'Summer Black' grapes. Melatonin spraying at 100 μmol L^-1 on grapes during veraison induced skin coloration earlier than that in controls, as well as higher transcript abundance of anthocyanin biosynthesis-related genes and transcription factors MYBA1 and MYBA2. Melatonin treatment increased the soluble sugar content, especially of sucrose, by promoting the activity of sucrose phosphate synthase, and also increased endogenous melatonin content and the concentrations of mineral nutrients N, K, Cu, Fe, and Zn in grape berries. Correlation analysis suggested that high sugar content promoted anthocyanin synthesis. These findings provide a sound theoretical basis for the development of techniques aimed to achieve optimum coloration of grapes in hot and rainy regions.