Effects of zınc to the growth and antıoxıdant enzyme actıvıty of Scenedesmus Ellıpsoideus Chodat

In this study, the effect of different (Zn) zinc concentrations (0, 1, 2, 4, 6 and 8 µg mL- 1 ) on Scenedesmus ellipsoideus was investigated through some growth and physiological parameters. For this purposes, changes in the biomass accumulation and chlorophyll a content were measured daily during the experiment (7 days). Our results showed that biomass accumulation, measured at 750 nm, represents a progressive increase in a time dependent manner at each Zn concentration during the experiment. Increased Zn concentrations, however, resulted in the decreased biomass values probably due to an impairment in cell division mechanism in S. ellipsoideus. Similarly, chlorophyll a content was decreased as the Zn concentration increased while this parameter showed irregular changes during 7 days, which may indicate a severe effect of Zn on photosynthetic pigment metabolism in S. ellipsoideus. The efficiency of metabolic defence responses of S. ellipsoideus under Zn toxicity was evaluated by the changes in some antioxidant enzymes. Accordingly, total superoxide dismutase (SOD), manganese superoxide dismutase (MnSOD), iron superoxide dismutase (FeSOD), activities increased up to 4 µg mL-1 Zn and then decreased. These results may show that Zn concentrations higher than 4 µg mL-1 inhibited SOD izozymes such as MnSOD and FeSOD and resulted in superoxide accumulation in S. ellipsoideus cells. In accordance to SOD activity, total ascorbate peroxidase (APX), activity increased slightly at Zn concentration higher than 2 µg mL-1 and decreased at 8 µg mL- 1 Zn concentration. This result clearly indicated that higher Zn concentrations led to hydrogen peroxide accumulation in S. ellipsoideus cells. Glutathione reductase, (GR) activity, however, did not show significant changes at all applied Zn concentrations. As a result, it may be concluded that higher Zn concentrations result in superoxide radical and hydrogen peroxide accumulation in S. ellipsoideus cells. Further, these harmful compounds may lead to photooxidaiton in chlorophyll a molecules and decrease growth rate. Finally, the absence of reduced glutathione accumulation, as indicated by constant GR activity under Zn toxicity, may be responsible for the lower efficiency of antioxidant defence system.