KINETIC STUDIES OF MINERAL UPTAKE AND ENZYME ACTIVITIES OF ANABAENA DOLIOLUM UNDER METAL STRESS

Abstract

Effect of Cd, Cu, Ni, Fe and Al on the kinetics of NO₃^-, NH₄⁺, urea and PO₄^3- uptakes, nitrate reductase, glutamine synthetase, urease, alkaline phosphatase and ATPase activities revealed a common pattern of inhibition, but the intensity of toxicity was metal specific. A ligand-based toxicity was observed in the case of Al but not for Cu and Ni. A non-competitive inhibition of NO₃^- uptake and NR activity suggested an irreversible inhibition of uptake and assimilation of NO₃^- by the test metals used. Contrary to this the competitive inhibition of NH₄⁺ uptake and glutamine synthetase suggested an active NH₄⁺ metabolism even under metal stress. Further, the competitive inhibition of uptake and assimilation of urea by metals confirmed that in absence of NH₄⁺ the alga can metabolize urea and meet its nitrogen demand. The test metals failed to interrupt PO₄^3- metabolism when external PO₄^3- pool was high or the organism was a PO₄^-3 accumulating one. This study suggested that for surviving in metal-stressed condition the cyanobacterium shifts from N₂/NO₃^- to NH₄⁺ utilization pathway.