Exogenous melatonin delays postharvest fruit senescence and maintains the quality of sweet cherries

We assessed the effects of postharvest exogenous melatonin (50,100 and 150 mu mol L-1) on the senescence and quality of sweet cherries during storage at 0 +/- 0.5 degrees C. Melatonin treatment decreased decay incidence, respiration rate, and weight loss. It delayed the degradation of firmness, lightness, saturation, hue angle, titratable acidity, and total soluble solids content, thus maintaining better fruit quality. Melatonin treatment inhibited increases in O-2(center dot)-, H2O2 malondialdehyde content, and relative membrane permeability, while maintaining higher endogenous melatonin levels and increasing superoxide dismutase and catalase activity. Additionally, melatonin treatment enhanced the activity of antioxidant enzymes, increased the levels of ascorbic acid, and reduced glutathione levels, which are related to the ascorbate-glutathione cycle, as well as increasing the AsA:DHA and GSH:GSSG ratios. Delayed senescence in sweet cherries after exogenous melatonin treatment may be associated with high endogenous melatonin levels and increased antioxidant activity and content.