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

Effect of Cd, Cu, Ni, Fe and Al on the kinetics of NO3-, NH4+, urea an d PO43- uptakes, nitrate reductase, glutamine synthetase, urease, alka line phosphatase and ATPase activities revealed a common pattern of in hibition, but the intensity of toxicity was metal specific. A ligand-b ased 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 tes t metals used. Contrary to this the competitive inhibition of NH4+ upt ake 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 a lga can metabolize urea and meet its nitrogen demand. The test metals failed to interrupt PO43- metabolism when external PO43- pool was high or the organism was a PO43- accumulating one. This study suggested th at for surviving in metal-stressed condition the cyanobacterium shifts from N2/NO3 to NH4+ utilization pathway.