Excess Zn alters the nutrient uptake and induces the antioxidative responses in submerged plant Hydrilla verticillata (L.f.) Royle.

To investigate the effects of zinc (Zn) on aquatic macrophyte, the submerged plant Hydrilla verticillata (L.f.) Royle was cultured in control solution or together with 0.05-30 mg L(-1) Zn(2+) for 7 d. The alterations in nutrient uptake and antioxidative response were assayed. Zn stress increased the uptake of Cu, Fe, Mn, Mg, and Zn while decreased that of P. Compared with control plants, the synthesis of chlorophyll was stimulated at 0.05-0.5 mg L(-1) Zn but inhibited at concentrations >5 mg L(-1), while the activity of NADH oxidase was suppressed at low level of Zn(2+) (0.05-5 mg L(-1)) but activated at concentrations of 30 mg L(-1). There were not significant changes in the content of malondialdehyde and activity of lipoxygenase, catalase, and glutathione S-transferase in the presence of Zn concentrations up to 0.5 mg L(-1) Zn, while at high concentrations significant increase in these parameters was observed. Meanwhile, activity of total superoxide dismutase increased in all treatments compared with control plants. The activity of guaiacol peroxidase and ascorbate peroxidase increased at 0.5-30 mg L(-1) Zn, and that of glutathione reductase increased at concentration of 0.05-0.5 mg L(-1) Zn but decreased significantly at 5-30 mg L(-1). In addition, some important antioxidative metabolites such as ascorbate, dehydroascorbate, glutathione and oxidized glutathione increased significantly in leaves treated with 10-30 mg L(-1) Zn when compared with control plants. These results suggested that Zn induced the nutrient imbalance and oxidative damage and the accelerated operation of antioxidative reactions might provide H. verticillata (L.f.) Royle with the enhanced Zn-stress tolerance.