Melatonin treatment delayed fruit softening by regulating postharvest carbohydrate metabolism of hami melon

Melatonin (MT) treatment has been proven to improve fruit quality. Herein, the efficacy of 0.5 mmol L^-1 MT treatment on carbohydrate metabolism, fruit softening, and their relationship during storage of harvested Hami melons was investigated. The results indicated that compared with those in control group, MT treatment markedly delayed fruit softening and the total soluble solids/titratable acid ratio, inhibited cell wall polysaccharide degradation, and maintained the cell wall integrity in Hami melons. Besides, MT treated also increased the starch, sucrose, and sorbitol contents, enhanced sucrose phosphate synthase and sucrose synthase synthesis activities, whereas reduced pectin methyl esterase, polygalacturonase, cellulase, β-galactosidase, β-glucosidase, xyloglucan endotransglycosylase, amylase, sucrose synthase-cleavage, acid invertase, neutral invertase, sorbitol oxidase, NAD-sorbitol dehydrogenase, NADP-sorbitol dehydrogenase activities in Hami melons. Additionally, MT treatment downregulated the expression levels of CmPG, Cmβ-gal, CmAmy, CmAI, CmNI and CmSOX, and upregulated the expression of CmSPS. Collectively, MT could slow fruit softening and prolong its shelf life by regulating carbohydrate metabolism.