Cadmium toxicity and phytochelatin production in a rooted-submerged macrophyte Vallisneria spiralis exposed to low concentrations of cadmium.

Phytochelatins (PCs) have been involved in metal detoxification, and used as potential biomarkers for an evaluation of metal toxicity. However, most studies have generally been limited to high concentrations of metals. In this study, low concentrations of cadmium (Cd) (0.01-0.64 microM) usually present in moderately polluted environments were adopted to investigate Cd toxicity, PC production, and their relationship in a rooted-submerged macrophyte Vallisneria spiralis. It was observed that 0.01-0.04 microM Cd had no significant effects on the growth of this plant when compared with the control plant without Cd, whereas 0.08-0.64 microM Cd showed toxicity, as indicated by the gradual decreases of leaf and root fresh weights. Cadmium accumulation was significantly higher in leaves than in the roots. Correspondingly, PCs were induced in leaves and roots at every Cd concentrations studied, in particular 0.16-0.64 microM, which were higher in leaves than in roots. There existed a positively linear relationship between PC concentrations and Cd toxicity in leaf and root. Furthermore, the levels of glutathione (GSH) in leaves and roots increased with increasing Cd concentrations in solutions and exposure time, but the extent of such increase was lower than that of PCs. Cadmium uptake antagonized Zn uptake. Combined effects of Cd and Fe or Cd and Mn were antagonistic in leaves and synergistic in roots. On the basis of the present results, it was further suggested that PCs can be used as potential biomarkers for monitoring the metal toxicity in moderately polluted environments.