Exogenous Sodium Nitroprusside Treatment Delays Postharvest Broccoli Yellowing by Inhibiting Endogenous Ethylene Synthesis

Postharvest broccoli yellowing severely limited the development of the broccoli industry and led to a waste of resources. In this paper, sodium nitroprusside was selected as an exogenous treatment to evaluate its effect on the greening to yellowing of broccoli. The 200 μmol/L SNP treatment protected the apparent quality of broccoli, as evidenced by the delayed increase in the yellowing index, L* value and decrease in –a/b value. It was also found that the treatment delayed the decrease of chlorophyll fluorescence parameters F_v/F_m and Rfd, which supplemented the evidence that SNP could delay the yellowing process of broccoli. It was also noted that the higher chlorophyll content in the treated group compared to the control group was due to the fact that the SNP treatment limited the increase in the activities of chlorophyll-degrading enzymes pheophorbide a oxygenase, non-yellow coloring 1, pheophytinase, and chlorophyllase. This view was supported by the suppression of the up-regulated expression of genes related to chlorophyll catabolism after SNP treatment. Moreover, the exogenous SNP treatment inhibited endogenous ethylene synthesis during the shelf period, which was mainly manifested by the down-regulation of the expression of ethylene synthesis genes BoACO3, BoACO4, and BoACS2 and the inhibition of the activities of the enzymes 1-aminocyclopropanecarboxylic acid synthase and 1-aminocyclopropanecarboxylic acid oxidase, thereby controlling the release of ethylene during the shelf period. The above results provide data support for the commercialization of SNP as a preservative.