The susceptibility of superoxide dismutase in Lemna minor to systemic copper concentrated from wastewater

Lemna minor (duckweed) was grown for 7 days in secondary-treated domestic wastewater containing additions of total Cu from 0.024–0.220 mg/l. Starch gel electrophoresis of plant extracts followed by enzyme staining showed that activity of one of four isozymes, probably Mn-SOD, was inhibited in Lemna containing 408 μg Cu/g (dry wt) but not in plants containing 215 μg Cu/g (dry wt) or less. Measurement of SOD activity in a reaction mixture showed significant ( P < 0.05) reduction in activity in extracts made from plants containing 408 μg Cu/g (dry wt) but no reduction in activity when plants contained 215 μg Cu/g (dry wt) or less. The four isozymes found in Lemna were tentatively identified by CN-sensitivity as two each of Cu,Zn-SOD and Mn-SOD. The activity of SOD in Lemna grown in defined medium was measured at 12 U/mg total protein.