Effect of melatonin treatment on improving jasmonates content and cell wall stability involved in enhanced chilling tolerance of peach fruit during cold storage

Peach fruit are prone to chilling injury (CI) during unsuitably low-temperature postharvest storage, and exogenous melatonin has been reported to confer chilling tolerance to peach fruit. However, the underlying mechanisms that enable this function remain largely unclear. In this study, peach fruit were dipped in 0.1 mmol L-1 melatonin solution for 30 min and then stored for 28 days at 4 degrees C. The results showed that the melatonindecreased CI and decay of peach fruit was accompanied by reductions in the content of respiratory rate, radical oxygen species, relative electrolyte leakage and malondialdehyde during storage. Transcriptome analysis identified many differentially expressed genes from peach fruit upon melatonin treatment on days 14 and 21. They were mostly associated with alpha-linolenic acid metabolism, glutathione metabolism and plant hormone signal transduction. Exogenous melatonin treatment enhanced the content of jasmonic acid (JA) and methyl jasmonate (MeJA) via upregulating expression of PpLOX, PpAOS, PpAOC and PpJMT in alpha-linolenic acid metabolism, which may contribute to activating the JA signaling pathway. Moreover, melatonin treatment was beneficial for activating glutathione metabolism in relation to enhancing the content of ascorbic acid, glutathione and maintaining a higher ratio of unsaturated fatty acids/saturated fatty acids. These results suggested that melatonin treatment improved JA and MeJA contents via alpha-linolenic acid metabolism and maintained cell wall stability, which might contribute to the enhanced cold tolerance in peach fruit during cold storage.