Abstract: To investigate the regulatory effect of exogenous dopamine on the quality of postharvest pak choi (Brassica rapa subsp. chinensis), the present study was conducted to determine the surface color, chlorophyll content, the expression of chlorophyll metabolism-related genes, the content of antioxidants, and the activity and gene expression of antioxidant enzymes in pak choi treated postharvest with different concentrations of dopamine hydrochloride solution and stored at (20 ± 1) ℃ and 80%–90% relative humidity (RH). The results showed that 600 μmol/L dopamine treatment reduced the expression of chlorophyll metabolism-related genes (BrNYC1, BrNOL, BrSGR1/2, BrPAO, and BrRCCR), inhibited chlorophyll degradation in postharvest pak choi; and down-regulated the gene expression of respiratory burst oxidase homologs (BrRbohC, BrRbohD, BrRbohE, and BrRbohG) to different degrees, which effectively reduced the accumulation of malondialdehyde (MDA) (18.6%) and superoxide anion radical (50.7%), and significantly increased the scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals (64.0%). Meanwhile, it differentially increased the gene expression of antioxidant enzymes (BrPOD, BrSOD, and BrCAT) to increase the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). In addition, compared to the control group, the dopamine treatment increased the contents of ascorbic acid (7.4%) and total phenols (27.1%), thereby delaying the postharvest senescence of pak choi. The findings of this study revealed that dopamine maintains the postharvest quality of pak choi through the regulation of chlorophyll metabolism, reactive oxygen species (ROS) balance and the antioxidant system, which provides new strategies and ideas to improve the quality and prolong the shelf-life of postharvest leafy vegetables.

Key words: dopamine; pak choi; postharvest senescence; chlorophyll; antioxidant