Spraying L-phenylalanine during fruit development alleviates chilling injury in harvested muskmelons by regulating membrane lipid metabolism

L-phenylalanine (L-Phe) is an aromatic essential amino acid. Although postharvest L-Phe treatment can alleviate chilling injury (CI) of fruit by scavenging excessive reactive oxygen species (ROS), there are no reports on whether L-Phe spraying during fruit development affects the CI of harvested muskmelon by regulating membrane lipid metabolism. In this study, plants and fruit of muskmelon (cv. Manao) were sequentially sprayed with 8 mM L-Phe four times at the young fruit stage, early expansion stage, late expansion stage and mature stage. The effect of L-Phe spraying during fruit development on CI of harvested muskmelon fruit was studied and to the related mechanism of membrane lipid metabolism was investigated. The results showed that L-Phe sprays activated phospholipase A2 (PLA2) and increased the content of unsaturated fatty acids such as linoleic acid, linolenic acid and oleic acid, and improved the double bond index of unsaturated fatty acids (DBI) in harvested muskmelons during cold storage. L-Phe sprays inhibited the phospholipase C (PLC) and phospholipase D (PLD), increased the content of phosphatidylinositol (PI) and phosphatidylcholine (PC), but decreased the content of phosphatidic acid (PA) in harvested muskmelons during cold storage. In addition, L-Phe sprays inhibited lipoxygenase (LOX), reduced malondialdehyde (MDA) levels and cell membrane permeability, and effectively reduced the CI index of harvested muskmelons during cold storage. Taken together, L-Phe sprays during fruit development alleviated CI in harvested muskmelons by regulating membrane lipid metabolism.