RESUMO
The tolerance of plants to Cd is a scientific and interesting issue for phytoremediation. In the current study, we attempt to reveal the physiological mechanism of the tolerance of Eichhornia crassipes to cadmium (Cd) by using hydroponic experiments. The results showed that the Cd absorption of E. crassipes was dose-dependent and the absorbed Cd was mainly maintained in the root. The fresh weight was greatly affected by Cd in the early stage of aquatic cultivation. The negative effect of Cd on E. crassipes is dose-dependent, but E. crassipes might adapt to moderate Cd pollution over time. The Cd stimulated the opening of the stomata, and the cell tightness ratio of E. crassipes increased with rising Cd concentrations. The administration of moderate levels of Cd stimulated the release of soluble protein, free proline, malondialdehyde, and soluble polysaccharide. Cd administration also stimulated the activity of superoxide dismutase, peroxidase (POD), catalase, and ascorbic acid peroxidase of E. crassipes, except for POD activity at the highest Cd concentration. This indicates that the physiological mechanism of the tolerance of E. crassipes to Cd depends on osmotic regulation, reduction of lipid peroxidation, improvement of antioxidant properties, increasing palisade tissue while decreasing sponge tissue, and increasing stomatal conductance.
