Exogenous melatonin promotes anthocyanin accumulation and coloration in Chinese plum peels.

Melatonin (MT) is a growth regulator that influences anthocyanin synthesis during plant growth. However, the regulation mechanism of MT on the coloration of plum peels remains unclear. Here, the effects of MT on the anthocyanin accumulation and coloration in Chinese plum peels were examined after MT (100 μmol/L) or water (control) treatment. The results showed that MT treatment accelerated the changes in plum peels from green to red by increasing the anthocyanin and phenolic contents. MT treatment also increased the antioxidant capacity, including the scavenging capacity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP); and promoted the enzyme activities of anthocyanin synthesis, such as chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), chalcone isomerase (CHI), and UDP-glucose 3-O-glucosyltransferase (UFGT). Moreover, transcriptome analysis indicated that MT treatment up-regulated the expression of several key anthocyanin-related genes, including CHS, F3H, dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), and UFGT, revealing the regulatory role of MT in anthocyanin metabolism. In conclusion, MT treatment can promote the anthocyanin accumulation and coloration in plum peels.