Phytotoxic effects of copper on nitrogen metabolism and plant growth in Brassica pekinensis Rupr.

Copper (Cu) from various anthropogenic and natural sources is one of the major heavy metal contaminants in the environment. To study Cu-induced nitrogen (N) metabolism damage in the popular vegetable Chinese cabbage (Brassica pekinensis Rupr.), aquatic culture experiments with this plant were performed. Two Cu levels (0.3 micromol/L (control) and 10.3 micromol/L) and two N levels (0.05- and 1-fold Hoagland's solution) were used for the aquatic culture experiments. The results demonstrated adverse effects of Cu on N metabolism and plant growth. Cu exposure elevated Cu concentration and decreased nitrate reductase (NR) activity in the roots and shoots and reduced total chlorophyll content. It also shortened root length and produced fewer leaves and lower plant biomass. However, Cu exposure increased total free amino acid content in the leaves. The results also demonstrated effects of N deficiency on N metabolism and plant growth. N deficiency increased the root/shoot ratio of biomass and the total free amino acid content and decreased the nitrate contents and NR activity in roots and leaves. In addition, there were interactive effects between Cu exposure and N level on plant biomass, root/shoot ratio, and chlorophyll and nitrate content in leaves. The results suggested that Cu toxicity to the plant was at least partly due to an influence on N metabolism.