Effects of sunburn on AsA-GSH cycle in pomegranate pericarp
To study the response of AsA-GSH cycle in pomegranate pericarp to sunburn, sunburn sensitive cul-tivar 'Hongyushizi' was used to study the changes of H2O2 and O2-· contents, AsA and GSH contents in the pericarps suffer from sunburn, besides, the changes of metabolites in the glutathione metabolism pathway and the expression levels of key genes involving in the AsA-GSH cycle were analyzed. The results showed that the contents of H2O2 and O2-· in pomegranate pericarp were increased significantly due to sunburn. The content of GSH in the sunburn pericarp was increased significantly, while the content of AsA was increased significantly only when severe sunburn occurred. The contents of 13 metabolites in the glutathione metabolic pathway in pomegranate pericarp were changed under sunburn, among which 4 metabolites were significantly up-regulated and 9 metabolites were signifi-cantly down-regulated. The expression of Pgr-GR-2 was significantly increased with the severity of sunburn, but the expression of Pgr-GR-2 in the pericarp of SB3 was slightly decreased compared with that of SB2. The expression levels of Pgr-APX-3 and Pgr-DHAR-1 were significantly increased under SB1, but which were decreased as the de-gree of sunburn increased. The expression of Pgr-MDHAR-1 decreased as the degree of sunburn increased. When the sunburn degree reached SB3, the expression of Pgr-MDHAR-1 was significantly lower than CK. Sunburn activated the expression levels of Pgr-GR-2, Pgr-APX-3 and Pgr-DHAR-1 genes in the AsA-GSH cycle of the pomegranate pericarp, repressed the expression of Pgr-MDHAR-1 gene, and further increased the contents of AsA and GSH to remove the damage caused by the increase of H2O2 and O2-·. These findings provide an insight into the sunburn mechanisms of pomegranate, and also into the effective prevention of fruit sunburn in pomegranate.
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