Exogenous ethylene alleviates chilling injury of 'Huangguan' pear by enhancing the proline content and antioxidant activity

Peel browning spots (PBS) is a chilling injury (CI) symptom in cold-stored 'Huangguan' pear. In the present study, the effect of exogenous ethylene on CI and its correlation to proline and reactive oxygen species (ROS) metabolism was investigated. The results showed that ethylene treatment (100 mu L L-1 for 24 h) could completely inhibit PBS appearance without significantly affecting fruit firmness, soluble solids content (SSC) and titratable acidity (TA), enhance ethylene production rate at the initiate stage of storage, and promote proline accumulation by increasing activities of pyrroline-5-carboxylate synthetase (P5CS), ornithine-delta-aminotransferase (OAT) and up-regulating expression of P5CS1 and OAT1 genes, decreasing proline dehydrogenase (PDH) activity and the expression of PDH1 gene in peel. Moreover, the ethylene treatment suppressed the accumulation of H2O2, O-2- and malondialdehyde (MDA), maintained higher levels of ascorbic acid (MA) and glutathione (GSH), and meanwhile enhanced activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as expression of the genes such as SOD1, CATI, and APX1 which could encode these enzymes in peel. These results suggested that ethylene alleviated the CI of 'Huangguan' pear by promoting the proline accumulation and antioxidant activity of peel.