Different response of phytochelatins in two aquatic macrophytes exposed to cadmium at environmentally relevant concentrations
Phytochelatins (PCs) have been proposed as potential biomarkers for an evaluation of metal toxicity. However, most studies have been generally limited to high concentrations of metals. In this study, two submerged macrophytes Ceratophyllum demersum L. and Elodea canadensis Michx. were adopted to investigate the response of phytochelatins (PCs) and its relationship with cadmium (Cd) toxicity upon exposure to low concentrations of Cd (0.01 to 0.64 μM) usually present in low or moderately polluted environments. It was observed that, 0.01 to 0.04 μM Cd had no obvious toxic effects on the growth of two plants compared with the control plants, whereas Cd toxicity is significantly seen in C. demersum at 0.08 to 0.64 μM and in E. canadensis at 0.16 to 0.64 μM, as indicated by the significant decreases of fresh weights. Two plants showed strong capacity to accumulate Cd present in low concentrations. PCs were produced in a dependent-species and-concentration manner. Response of PCs was strong in C. demersum exposed to Cd concentrations studied (0.02 to 0.64 μM) and dramatically increased with the increase of Cd concentrations in solutions. The maximum amount of PCs in C. demersum was found at 7 days and obviously decreased with the prolonged exposure to Cd. PC concentrations in C. demersum were positively correlated with Cd toxicity, as measured by the growth inhibition rate of fresh weight. By contrast, Cd concentrations studied slightly or mildly induced the production of PCs in E. canadensis. The results suggested that, positive responses of PCs in C. demersum can serve as early biomarkers for reflecting Cd toxicity in low or moderately polluted water environments.
Key words: Biomarker, cadmium, Ceratophyllum demersum L., Elodea canadensis Michx., metal toxicity, phytochelatins.