Melatonin reduces postharvest decay of blueberries by regulating ascorbate–glutathione cycle and membrane lipid metabolism

Postharvest fruit storage and quality is a severe concern for fruit producers, as consumer acceptability and market value are affected by quality attributes. Therefore, strategies to improve fruit quality during storage are crucial. In this study, we investigated the effects of melatonin (MT) treatment on postharvest fruit quality, ascorbate-glutathione metabolism, and membrane lipid metabolism in blueberries. Blueberries were treated with 300 μM of MT solution or distilled water (control) before harvest. After harvest, blueberries were stored at 4 °C and sampled every 4 days to analyze fruit quality parameters. MT treatment effectively reduced decay rate and weight loss rate in blueberry during storage and delayed the decrease in firmness, total soluble solids, titratable acid, anthocyanins, and flavonoids. It furthermore elevated the activities and gene expression of enzymes such as superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, dehydroascorbate reductase, and monodehydroascorbate reductase. Moreover, MT treatment promoted the accumulation of ascorbate–glutathione, NADP, NADPH, and glutathione, increased glutathione (GSH)/glutathione (GSSG) levels, enhanced antioxidant capacity, and decreased oxidized glutathione, H₂O₂, dehydroascorbic acid, and superoxide anion levels. Notably, MT treatment inhibited membrane lipid peroxidation in blueberries by inhibiting the mRNA levels and activities of lipoxygenase and phospholipase D. Conclusively, MT reduces blueberry decay during storage by modulating ascorbate–glutathione cycle and membrane lipid metabolism.