L-Cysteine Treatment Delays Leaf Senescence in Chinese Flowering Cabbage by Regulating ROS Metabolism and Stimulating Endogenous H2S Production

Leaf senescence is a major concern for postharvest leafy vegetables, as leaves are highly prone to yellowing and nutrient loss, resulting in reduced commercial value and limited shelf-life. This study aimed to investigate the effect of L-cysteine (L-cys) on postharvest Chinese flowering cabbage stored at 20 °C. The results showed that 0.5 g L^-1 L-cys treatment effectively slowed leaf senescence by downregulating chlorophyll degradation genes <i>(BrNYC1, BrNOL</i>, <i>BrPPH</i>, <i>BrPAO</i>, <i>BrNYE</i>, and <i>BrSAGs</i>) and senescence marker gene <i>BrSAG12</i>. Moreover, this treatment exhibited positive influence on the nutritional quality of cabbage. Also, L-cys treatment maintained ROS homeostasis, preventing excessive ROS accumulation and lipid membrane oxidation. L-cys treatment also maintained a higher total antioxidant capacity and scavenging rate of •OH and O₂^•-. Additionally, L-cys treatment maintained high levels of ascorbate and glutathione and activated antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and the expression of the encoding genes. Furthermore, L-cys treatment elevated endogenous H₂S levels, which are correlated with increased L-cysteine desulfhydrase activity and the upregulation of H₂S biosynthesis-related genes. These findings suggest that L-cys can delay leaf senescence by reducing chlorophyll breakdown, maintaining ROS homeostasis, and stimulating endogenous H₂S production.