Antioxidant enzymes and proteins of wetland plants: their relation to Pb tolerance and accumulation.

Constructed wetlands used to clean up toxic metals such as lead (Pb) from contaminated wastewater are considered as an effective and low-cost technology. The effect of Pb on the biomass, tolerance, soluble protein, and antioxidant enzymes in 18 candidate wetland plant species grown in soils without (control) and spiked with 900 and 1800 mg Pb kg(-1) was studied in a pot trial. Our pot experiment showed that the biomass, tolerance, and leaf protein contents decreased with increasing concentrations of Pb in soil. There were significant differences between the plants in their Pb tolerance indices (29-82 % in the 900 mg Pb kg(-1) amended soil) and also Pb uptake (13-749 mg kg(-1) in shoots and 1112-4891 mg kg(-1) in roots, in the same treatments). Activities of superoxide dismutase (SOD) and peroxidase (POD) in leaves of most of the plants increased with increasing level of soil Pb concentration. Conversely, catalase (CAT) activity in leaves declined when plants were subjected to Pb stress. Lead accumulation by the 18 wetland plant species screened was strongly dependent on the species and Pb concentrations in the soil. However, Pb translocation from root to shoot was generally low in all species. Increases in SOD and POD activities suggest that the antioxidant system may play an important role in alleviating Pb toxicity in wetland plants. The data obtained should help in future species selection for the use in designing wetlands in Pb-contaminated environments.