Exogenous melatonin maintains quality of postharvest Rosa roxburghii fruit by modulating reactive oxygen species metabolism and energy status

Antioxidant capacity and energy status are closely associated with the quality of fruit. The effect of exogenous melatonin on the quality, reactive oxygen species (ROS) and energy metabolism of Rosa roxburghii fruit was investigated in this study. The results demonstrated that 50 mu M melatonin postponed the increase in decay incidence, weight loss and malondialdehyde content and the decrease in fruit firmness, total soluble solids and titratable acid of R. roxburghii. Melatonin also reduced hydrogen peroxide content while enhancing glutathione and ascorbic acid contents by increasing the activity of enzymes involved in ROS metabolism, including superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase and dehydroascorbate reductase. 50 mu M melatonin enhanced the activity of H+-ATPase, Ca2+-ATPase, succinate dehydrogenase and cytochrome C oxidase, the levels of ADP and ATP, while decreasing the content of AMP. Moreover, the expression levels of L-ascorbic acid (AsA) biosynthesis and recycling-related genes RrGME, RrGMP, RrGGP, RrGalDH, RrAPX, RrGR, RrDHAR and RrMDHAR were significantly up-regulated in melatonintreated fruit. These results indicated that melatonin could maintain the quality of R. roxburghii through regulating ROS and energy metabolism during storage.