Role of Exogenous Melatonin in Quality Maintenance of Sweet Cherry: Elaboration in Links Between Phenolic and Amino Acid Metabolism

Melatonin (MT) was closely contributed to quality maintenance of postharvest fruits. In this study, sweet cherries were soaked in 100 mu M MT for 30 min, and the morphological characteristics, textural attributes, contents and composition of phenolics, amino acids and endogenous MT were measured for evaluating the contribution of exogenous MT during storage at 20 degrees C for 9 d. Results showed that MT treatment delayed decreases of lightness (L*), chromaticity (C*), total soluble solids (TSS) and titratable acidity (TA), and maintained the visual appearance of sweet cherries. And the weight loss and membrane permeability of MT-treated fruits were 17.26% and 9.1% respectively lower than that in CT on day 9, but accompanied with 24.65% higher firmness. Furthermore, LC-MS and q-PCR were used to assess links between phenolic, amino acid and endogenous MT metabolisms, suggesting the improvement of endogenous MT content and transcriptional up-regulation of key genes as influenced by exogenous MT. Similar positive effect on phenolic biosynthesis and accumulation was observed. Besides, the increase of amino acids in MT-treated fruits especially on Phe and Try, precursors of phenolic and MT pathways, further provided evidence on the role of endogenous MT in the quality maintenance of postharvest sweet cherries.