Melatonin improves the postharvest quality of grape (Vitis vinifera L.) by modulating cuticular wax, cell wall, and phenolic metabolism

Grapes are rich in diverse nutritional ingredients; however, they are perishable, posing challenges during postharvest storage. Melatonin (MT) regulates the physiological properties of fruit during the postharvest period. In this study, the ‘Red Globe’ grapes (Vitis vinifera L.) were treated with 100 μmol L⁻¹ MT solution and stored under cold condition for 56 d. Results showed that exogenous MT application maintained wax structure and delayed the degradation of cuticular wax. At the end of storage, the total cuticular wax content with MT treatment was increased by 26 % compared with that in the control. MT treatment stimulated the transcription of key genes involved in wax biosynthesis. Moreover, MT treatment inhibited the activity of pectin methyl esterase (9 %), polygalacturonase (24 %), and β-galactosidase (13 %), which slowed down the decrease in chelate-soluble pectin (19 %), and Na₂CO₃-soluble pectin (5 %) levels. In addition, MT treatment maintained higher levels of phenolic compound by up-regulating key biosynthetic genes. In summary, these results indicate that MT preserved postharvest quality of grape berries by regulating cuticular wax, cell wall, and phenolic metabolism.