Role of exogenous melatonin in table grapes: First evidence on contribution to the phenolics-oriented response.

Melatonin (MLT) has gained increasing attention due to its pleiotropic effects. In present study, 'Kyoho' grapes were immersed in 200 μM of MLT to investigate the role of exogenous melatonin in postharvest metabolism response. Results indicated that berry abscission and rotten index was reduced by 37.50% and 58.37%, respectively, by exogenous MLT treatment, while the amino acid accumulation was greatly enhanced. Furthermore, the endogenous MLT biosynthesis was activated, where the transcript expression of genes, encoding tryptophan decarboxylase, tryptophan decarboxylase, N-acetylserotonin methyltransferase and N-acetyltransferae were upregulated significantly (p < 0.05), in accordance with the increase of endogenous MLT. Phenolic biosynthesis related genes were upregulated significantly, accompanied with the significantly higher phenolics content (p < 0.05). On day 15, the expression level of phenylalanine ammonia-lyase in MLT-treated group was twice of that in control. Therefore, this study provides the first evidence pertinent to the contribution of exogenous melatonin to the phenolics metabolism in postharvest table grape.