Preharvest salicylic acid treatment delays postharvest senescence in broccoli by regulating chlorophyll metabolism and reactive oxygen species homeostasis

Abstract Broccoli (Brassica oleracea L. var. italica) is a highly perishable vegetable that undergoes rapid postharvest senescence and yellowing, resulting in the loss of nutritional and bioactive compounds. To address this issue, the present study investigated the effects of preharvest salicylic acid (SA) spraying on the quality of broccoli after 25 d of storage at 4 °C. Compared with the control group, preharvest SA treatment, particularly at a concentration of 0.5 mmol/L (SA0.5), effectively maintained phenotypic appearance, suppressed changes in color parameters (L*, a*, b*, and H*), reduced weight loss, retained higher stem hardness, and increased soluble solids content. The application of SA also preserved the contents of total chlorophyll and chlorophyll b by inhibiting the activities and gene expression of key chlorophyll-degrading enzymes, including chlorophyllase, Mg-dechelatase, pheophytinase, and pheophorbide a oxygenase, thereby delaying yellowing. Additionally, SA treatment elevated hydrogen peroxide (H2O2) levels while decreasing superoxide anion (O2−·) accumulation. It increased superoxide dismutase activity while decreasing the activities of peroxidase and catalase, and enhanced the contents of non-enzymatic antioxidants such as vitamin C, total phenolics, and flavonoids. These results indicate that preharvest SA application contributes to delayed senescence in broccoli by modulating chlorophyll degradation and reactive oxygen species metabolism.