Exogenous application of glycine and nitrate on antioxidant and polyphenol metabolism in Brassica campestris spp. Chinensis

Abstract

Pakchoi (Brassica campestris ssp. Chinensis) is a leafy vegetable which has been widely cultivated and consumed worldwide due to its low calorific value, a large supply of macro and micronutrients, beneficial phytochemicals and fibers. Amino acids have a vital role in plant nutrition; however, the effect of glycine and nitrate (Gly/NO3-N) on health-promoting phytochemicals, biomass, and antioxidant activities has gained a little attention. Thus, this study aimed to evaluate the impact of glycine and nitrate on health-promoting phytochemicals and yield/biomass of pakchoi. Glycine and nitrate were employed in different proportions (control, Gly/NO3-N = 3:1, Gly/NO3-N = 1:1, and Gly/NO3-N = 1:3 in the Venlo greenhouse, Shanghai Jiao Tong university, China. Results showed that compared to control, the treatment with Gly/NO3-N notably increased the secondary metabolites like polyphenols, flavonoids, glutathione (GSH), ascorbic acid (vitamin C), antioxidant potential (FRAP and DPPH value), and biomass in pakchoi plants. The contents of all antioxidants were high under the treatment of Gly/NO3-N（1:1). Interestingly, the contents of flavonoids were significantly enhanced (107.10%) by Gly/NO3-N = 1:1 than control plants. Furthermore, the content of Phe increased by 33.79%-86.32%, and also the activity of catabolic enzymes (CHI, CHS, C4H, and PAL) of the polyphenols pathway was found to be significantly enhanced while the activity of 4CL and DFR was restrained by the treatment of Gly/NO3-N, compared with control plants. In addition, the correlation analysis of polyphenols and flavonoids with Phe, PAL, C4H, CHS, and CHI showed a positive correlation, while a negative correlation was found in the case of 4CL and DFR. Taken together, the current findings suggest that the application of Gly/NO3-N enhanced polyphenols metabolism as well as increased the total polyphenolic content and antioxidant activity. Consequently, this combination of glycine and nitrate could be used to promote beneficial phytochemicals and yield/biomass of pakchoi.