Sulfur dioxide mitigates oxidative damage by modulating hydrogen peroxide homeostasis in postharvest table grapes

The hydrogen peroxide (H2O2) burst accelerates the decay and senescence of table grapes. Sulfur dioxide (SO2), a commercial preservative, is known to maintain the postharvest quality of table grapes. However, the mechanism by which SO2 improves postharvest quality is still unclear. In this study, the effects of SO2 on sulfite reduction, the ascorbate-glutathione (AsA-GSH) cycle and the H2O2 receptor during storage were evaluated. The results showed that SO2 not only inhibited decay but also reduced the accumulation of H2O2 and malondialdehyde (MDA). Compared to the control, SO2 treatment increased the activities of sulfite reductase (SiR), serine acetyltransferase (SAT) and O-acetylserine (thiol)-lyase (OASTL), the content of cysteine (Cys) and the expression levels of VvSiR, VvSAT1, VvSAT2 and VvOASTL. Enhancement of critical enzyme activity, gene expression and antioxidant content in the AsA-GSH cycle was observed in SO2-treated grapes. Furthermore, VvGS expression was also determined to be involved in GSH synthesis. SO2 repressed the transcription level of VvHPCA1–4, and VvHPCA3 could be used as a candidate gene to evaluate the degree of oxidative damage in table grapes. These findings suggested that SO2 maintained H2O2 homeostasis to alleviate postharvest oxidative damage by activating sulfite reduction and the AsA-GSH cycle along with inhibiting the expression of VvHPCAs.