Lead induced antioxidant response and phenotypic plasticity of Scenedesmus quadricauda (Turp.) de Br,bisson under different nitrogen concentrations

The induction of antioxidant response and phenotypic plasticity of Scenedesmus quadricauda after exposure to lead (Pb) (3.6 x 10(-8) and 3.6 x 10(-7) M) at different nitrogen (N) concentrations (1.8 x 10(-4), 1.8 x 10(-5), and 1.8 x 10(-6) M) was investigated. The growth of the microalga was inhibited with decreasing N and increasing Pb concentrations. N limitation and Pb stress caused a decrease in biomass (cell density, dry weight, and chlorophyll a) production. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S transferase (GST) activities generally increased with N limitation and/or increased Pb stress. CAT and POD activities decreased after 48 h, even though their activities were still higher than in those in the control, while GST and SOD activities increased throughout the N/Pb stress exposure period. The enzyme activities observed in S. quadricauda showed a significant positive correlation with N/Pb stress. These results imply that aquatic biota may suffer differently from Pb toxicity, depending on the amount of nitrogen in the environment.