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 PO43- 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 PO43- metabolism when external PO43- 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.