Effect of copper on nitrogen uptake, transportation, assimilation processes, and related gene expression in Chinese cabbage [ Brassica campestris L. ssp. Chinensis (L.)] under various nitrate-to-ammonium ratios

Abstract

Improving vegetable yield and optimizing its quality through nutrient management have long been central to plant nutrition and horticultural science. Copper (Cu) is recognized as an essential trace element that promotes plant growth and development. However, the mechanisms by which Cu influences nitrogen (N) metabolism remain largely unknown, with limited studies exploring the interaction between Cu and varying nitrate-to-ammonium (nitrate/ammonium) ratios. In this study, Chinese cabbage was exposed to two Cu concentrations (0 and 0.02 mg L^-1) in combination with three nitrate/ammonium ratios (10/90, 50/50, and 90/10) under hydroponic conditions. The results showed that Cu application increased plant biomass, nitrate reductase (NR) and glutamine synthetase (GS) enzyme activities, the expression of NR (NIA) and GS2 (Gln2) genes, and N content in both shoots and roots. Additionally, Cu treatment decreased nitrate and free amino acid contents, as well as the expression of nitrate transporters NRT1.1 and NRT2.1 in roots while increasing these four parameters in shoots. Additionally, these effects were significantly modulated by the nitrate/ammonium ratios. In conclusion, Cu may facilitate nitrate transportation, enhance nitrate reduction, promote ammonium assimilation, and influence the transformation of organic N compounds, highlighting its potential role in improving N metabolism in Chinese cabbage.

Keywords: Chinese cabbage; copper; gene expression; nitrate/ammonium ratios; nitrogen metabolism.

Figure 1

The effects of Cu on nitrate (A, B) and ammonium (C, D) contents in Chinese cabbage shoots and roots under three nitrate/ammonium ratios. Significance levels are denoted by distinct lowercase letters at p < 0.05.

Figure 2

Effects of Cu on the expression of NRT1.1 (A, B) and NRT2.1 (C, D) in Chinese cabbage shoots and roots under three nitrate/ammonium ratios. Significance levels are denoted by distinct lowercase letters at p < 0.05.

Figure 3

The effects of Cu on NR activity (A, B) and NIA gene expression (C, D) in Chinese cabbage shoots and roots under three nitrate/ammonium ratios. Significance levels are denoted by distinct lowercase letters at p < 0.05.

Figure 4

The effects of Cu on GS activity (A, B), Gln1 (C, D) and Gln2 (E, F) expressions in Chinese cabbage shoots and roots under three nitrate/ammonium ratios. Significance levels are denoted by distinct lowercase letters at p < 0.05.

Figure 5

The effects of Cu on soluble protein (A, B) and total free amino acids (C, D) contents in Chinese cabbage shoots and roots under three nitrate/ammonium ratios. Significance levels are denoted by distinct lowercase letters at p < 0.05.

Figure 6

The effects of Cu on total N content (A, B) and N accumulation (C, D) in Chinese cabbage shoots and roots under three nitrate/ammonium ratios. Significance levels are denoted by distinct lowercase letters at p < 0.05. The ns represents insignificant change at the p < 0.05 level.