α-Lipoic acid treatment alleviates postharvest pericarp browning of litchi fruit by regulating antioxidant ability and energy metabolism

Litchi fruit has high commercial value and significant benefits for humans. However, pericarp browning, as the indicator of litchi fruit senescence, limits the shelf life of litchi fruit. Effect of α-lipoic acid (α-LA) that has great antioxidant potential, on litchi fruit senescence was investigated. Results showed that α-LA delayed pericarp browning and attenuated redox stress of litchi fruit, indicated by lower hydrogen peroxide (H2O2) and superoxide radical (O2−·) contents but higher hydroxy radical scavenging rate. Compared to control, α-LA treatment enhanced enzymatic: superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) as well as nonenzymatic antioxidants: glutathione (GSH) and ascorbate (AsA). Meanwhile, α-LA was protective against oxidative stress by inducing glutaredoxin (LcGrx), thioredoxin (LcTrx) and methionine sulfoxide reductase (LcMsr) expression levels. These α-LA-induced antioxidant systems directly increased the antioxidant capacity. Further research indicated that α-LA pretreatment maintained higher intracellular ATP level and activated extracellular ATP signaling through up-regulating LcDORN1s expression, indirectly increasing the antioxidant capacity. In conclusion, α-LA is effective to increase the antioxidant capacity and delay the pericarp browning of litchi fruit.