Preharvest Application of Sodium Nitroprusside Alleviates Yellowing of Chinese Flowering Cabbage via Modulating Chlorophyll Metabolism and Suppressing ROS Accumulation

Chinese flowering cabbage is prone to senescence andyellowingafter harvest, leading to a huge postharvest loss. Nitric oxide (NO)is a multifunctional plant growth regulator, but the effect of preharvestapplication of NO on the storage quality of Chinese flowering cabbageremains unclear. Preharvest application of 50 mg L-1 sodium nitroprusside (SNP, a NO donor) to the roots obviously reducedleaf yellowing in Chinese flowering cabbage during storage. Proteomicanalysis reveals 198 differentially expressed proteins (DEPs) in SNP-treatedplants compared to the control. The main DEPs were significantly enrichedin chlorophyll metabolisms, phenylpropanoid synthesis, and antioxidantpathways. SNP treatment enhanced chlorophyll biosynthesis and suppressedchlorophyll-degradation-related proteins and genes. It also modulatedflavonoid-biosynthesis-related genes, and 21 significantly regulatedflavonoids were identified in SNP-treated plants. The enhanced antioxidantcapacity in SNP-treated plants was able to decrease chlorophyll catabolismby inhibiting peroxidase-mediated chlorophyll bleaching. Collectively,preharvest SNP treatment modulated chlorophyll metabolism and preservedchlorophyll content in leaves during storage. Moreover, SNP treatmentenhanced flavonoid synthesis, suppressed reactive oxygen species accumulation,and delayed the senescence process, thereby maintaining leaf greeningin Chinese flowering cabbage. These findings highlight the role ofexogenous NO in alleviating yellowing of leafy vegetables.