Exogenous hydrogen sulphide alleviates senescence of postharvest pakchoi through regulating antioxidant system, endogenous hydrogen sulphide and nitric oxide metabolism

Previous studies showed that hydrogen sulphide (H2S) fumigation retarded the yellowing of detached pakchoi leaves. However, whether H2S regulated specific metabolic pathways and gene expression levels in this process remained unclear. In this study, the effect of H2S, DL-propargylglycine (PAG, H2S synthetic inhibitor) on antioxidant capacity, endogenous H2S synthesis, and endogenous NO synthesis in pakchoi was investigated. After H2S fumigation (40 L L−1, 6 h), the pakchoi stored at 20 °C ± 1 °C with 90–95% relative humidity exhibited the best quality, with the highest chlorophyll content and the lowest respiration rate and malondialdehyde content. Contrarily, PAG accelerated pakchoi senescence. H2S treatment reduced superoxide anion and hydrogen peroxide by increasing the activities of superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase, partially up-regulating the expression of enzyme genes. The increased expression of BcLCD, BcDCD and BcCAS C1 activated L- and D-cysteine desulfhydrase activities so that more endogenous H2S were retained in the pakchoi. Meanwhile, H2S treatment increased cysteine content in pakchoi via up-regulating BcSAT5 expression and enhancing the activities of sulfite reductase and serine acetyltransferase. Moreover, H2S increased endogenous NO primarily by preserving the activities of nitrate reductase and nitrite reductase instead of NO synthase (NOS)-like activity and decreased nitrate and nitrite as well. Overall, exogenous H2S alleviated the senescence of postharvest pakchoi via positively regulating antioxidant system, endogenous H2S and NO metabolism. Moreover, this work described a putative regulatory mechanism and provided some relevant information for future research into the interaction of H2S and NO in this process.