Effects of Pb2+ on the active oxygen-scavenging enzyme activities and ultrastructure in Potamogeton crispus leaves

The effects of various concentrations of Pb2+ on the antioxidant enzyme activities and the ultrastructure in Potamogeton crispus leaves were studied. Peroxidase (POD) activity and malondialdehyde (MDA) content peaks were observed with an increase in Pb2+ concentration, whereas superoxide dismutase (SOD) and catalase (CAT) activities decreased firstly and then rose. Meantime, the chlorophyll content declined with increasing Ph2+ concentration. Simultaneously, high concentrations of Ph2+ aggravated ultrastructural damage to the leaf cells including swelling of chloroplasts, disruption and disappearance of chloroplast envelopes; swelling of mitochondrial cristae, deformation and vacuolation of mitochondria; condensation of chromatin, dispersion of nucleoli, and disruption of nuclear membrane. Changes in antioxidant enzyme activities and damage to fine structure are the results of lead-induced ROS accumulation. The estimated lethal concentration to P. crispus ranged from 10 to 15 mg/l lead.