Interactive effects of UV-B and heavy metals (Cu and Pb) on nitrogen and phosphorus metabolism of a N2-fixing cyanobacterium Anabaena doliolum

Abstract

This study demonstrated a general decrease in uptake of NH4+, urea and PO43−, activities of nitrogenase, glutamine synthetase, urease, alkaline phosphatase and ATPase following ultraviolet-B (UV-B) treatment and metal exposure, separately. As compared with an individual stressor the effect of their combination was more detrimental to the above processes. In contrast, a significant increase in NO3− uptake and nitrate reductase activity, following exposure of Anabaena doliolum to UV-B was observed. Kinetic study of all the processes demonstrated that the UV-B-induced structural change(s) in the enzymes/carriers could be responsible for uptake and assimilation of these nutrients. However, the metals seem to compete for the binding sites of the above enzymes/carriers. A synergistic interaction of UV-B and metals (Cu/Pb) seems to be due to an increased metal uptake by an altered membrane permeability, as a result of peroxidation of membrane lipids in UV-B exposed cells.