Amelioration of chilling injury in 'Guifei' mango fruit by melatonin is associated with regulation of lipid metabolic enzymes and remodeling of lipidome

The susceptibility of harvested mango fruit to chilling injury (CI) restricts quality preservation. Cell membranes are recognized as primary sites of damage in fruits in response to cold stress, and the maintenance of membrane integrity and function is conducive to alleviating fruit CI. This study aimed to investigate the effects of melatonin (MT), an important bioactive molecule, on cold tolerance in relation to membrane lipid homeostasis in 'Guifei' mango fruit during refrigeration. The results showed that application of 0.5 mmol L-1 MT to mango fruit reduced the CI index, discoloration, relative electrolyte leakage (REL) and malondialdehyde (MDA) content while maintaining a higher Fv/Fm value. Reduced activities of phospholipase D (PLD), phospholipase C (PLC) and lipoxygenase (LOX) but increased phospholipase A2 (PLA2) activity were observed in MT-treated fruit compared to control fruit. Furthermore, lipidomic analysis revealed changes in molecular species profiles of various classes of lipids (phospholipids, lysophospholipids, sphingolipids and glycerides) in response to MT. These results indicate that MT could trigger remodeling of lipid molecules by regulating membrane lipid metabolism, which would be conducive to maintaining membrane structure and activating downstream signaling pathways, contributing to improved cold tolerance in mango fruit.