Abstract:

This study aimed to explore the effects of exogenous melatonin treatment on the fruit quality and anthocyanin metabolism of‘Taoxingli’plum fruit during storage. The‘Taoxingli’plum fruit about 70% maturity were harvested，and were soaked in water（as the control） or 0.1 mmol · L^-1 melatonin solution for 1 h and then dried in air. The fruit were stored at room temperature（25 ± 1）℃ and relative humidity of 75%-80% for 18 days，and the changes in color，firmness，decay rate，respiration rate，ethylene release，soluble solids content，and anthocyanin metabolism of the fruit were investigated during storage. The results showed that melatonin treatment inhibited the softening and decay of fruit，delayed in the color transformation，reduced respiration rate and ethylene release，postponed the ethylene release peak and the accumulation of carbohydrate in the fruit compared to the control. Melatonin treatment slowed down the anthocyanin accumulation in the fruit by inhibiting the expression of PsCHI gene and the activities of the enzymes involved in anthocyanin synthesis，including cinnamate carboxylase（C4H），4-coumaryl CoA ligase（4-CL），chalcone isomerase（CHI），flavanone hydroxylase（F3H），dihydroflavonol reductase（DFR）and anthocyanin synthetase（ANS） at the beginning time of storage，whereas at the later stage of storage，melatonin treatment significantly up-regulated the expressions of the structural genes including PsCHS，PsF3H，PsDFR，PsANS and PsUFGT related to synthesis of anthocyanins along with increases in the activities of C4H，4-CL，F3H，DFR and ANS，which could promote the synthesis of anthocyanins. Therefore，melatonin treatment not only delayed the process of fruit ripening，but also was of benefit to the accumulation of anthocyanins in the full-ripening fruit，which could be contributed to extending the shelf life and improving the nutritional value of fruit.

Key words: plum, fruit, melatonin, anthocyanin metabolism, quality, postharvest