Metal Uptake and Physiological Changes in Lemna gibba Exposed to Manganese and Nickel

We investigated the effects of manganese (Mn) and nickel (Ni) stress on pigment (total chlorophyll and carotenoid), total soluble protein content and antioxidant enzyme [superoxide dismutase (SOD) guaiacol peroxidase (POD) and catalase (CAT)] activities in Lemna gibba under laboratory conditions. L. gibba was treated with exposures of Mn and Ni separately at 0.25, 1, 4 and 16 mg/L concentrations for 72 hours at 24 h intervals. The results of the present study showed that the physiological status of L. gibba was affected by Mn and Ni exposure. Mn and Ni accumulations showed increases in a concentration dependent manner. The amount of accumulated Mn was higher than Ni at all concentrations and exposure times. Ni caused strong inhibition on the total chlorophyll and carotenoid amounts than Mn. The increase in the total protein content was more evident in Mn-exposed plants. The highest increase in SOD activity was evidenced in Ni-treated plants for all exposure times. However, the stimulating effect of Mn on CAT and POD activities was more evident than of Ni (except for 72. h). Based on these results it is concluded that Ni was found to be more toxic to L. gibba than Mn. Additionally, L. gibba may be used for phytoremediation of Mn in polluted aquatic environments.