Preharvest chitooligosaccharide spray alleviates chilling injury in harvested muskmelon fruit by regulating membrane lipid metabolism and activating antioxidant enzyme activity

Chitooligosaccharide (COS), a degradation product of chitosan, can reduce chilling injury (CI) in postharvest fruit by increasing antioxidant enzyme activity. However, whether preharvest COS spray alleviates CI in muskmelon fruit after harvest by regulating membrane lipid metabolism and increasing antioxidant enzyme activity has not been reported. In this study, muskmelon plants and fruit were sprayed with 2 mL L−1 of COS at four developmental stages: young fruit, early enlargement, late enlargement, and mature stage. The expression of key genes involved in membrane lipid metabolism, fatty acid content, phospholipid component content and antioxidant enzyme activity in muskmelon fruit were measured, and the CI symptoms and index of the fruit were observed during cold storage. The results illustrated that the preharvest COS spray up-regulated the expression of CmPLA2, promoted the release of unsaturated fatty acids, and increased the value of the double bond index (DBI). However, the spray down-regulated the expression of CmPLC and CmPLD, increased the levels of phosphatidylcholine (PC) and phosphatidylinositol (PI), and decreased the levels of phosphatidic acid (PA). COS spray increased superoxide dismutase (SOD) and catalase (CAT) activity, decreased O2-· and H2O2 levels, maintained cell membrane permeability, and decreased MDA levels in fruit during chilling. In addition, the spray reduced peroxidase (POD) activity and alleviated fruit pericarp browning during cold storage. Taken together, preharvest COS spray alleviated CI in muskmelon fruit by stimulating membrane lipid metabolism and improving the activities of antioxidant enzymes.