Nitric oxide regulates the lignification and carotenoid biosynthesis of postharvest carrot (Daucus carota L.)

The carrot is an important horticultural crop of the Apiaceae family, possessing considerable nutritional and economic value. Unfortunately, the decline in the postharvest quality has resulted in a decrease in the desirability of carrots and further food wastage. Nitric oxide (NO) plays a crucial role in alleviating the senescence and reducing losses of postharvest horticultural products, but its impact on the postharvest quality of carrots has not been reported. In this study, the effects of treatment with ddH2O, varying concentrations of sodium nitroprusside (SNP), and carboxy-PTIO (cPTIO) on the whiteness index, weight loss, and sensory scoring were evaluated, and a concentration of 1.5 mM SNP treatment preserved the appearance quality of postharvest carrots. Further analysis revealed that SNP treatment led to an increase in endogenous NO content by promoting nitrate reductase activity, which subsequently enhanced the expression of DcPSY1, DcPDS1, DcZDS1, DcCRTISO1, and DcLCYB1 and increased the levels of total carotenoid, alpha-carotenoid, and beta-carotenoid. The alternation of carotenoids both increased abscisic acid (ABA) level by promoting the expression of ABA biosynthesis genes, but also hindered the generation of hydrogen peroxide and superoxide anion. Meanwhile, the expression of lignin biosynthesis genes was downregulated in SNP treatment group, resulting in postharvest carrots with lower lignin content and a lower degree of cell lignification. Overall, our findings provide a theoretical basis for the application of NO in the postharvest preservation of carrots and shed light on the role of NO in regulating the synthesis mechanisms of carotenoids and lignin in postharvest carrots.