INTERACTIVE EFFECTS OF UV-B AND HEAVY-METALS (CU AND PB) ON NITROGEN AND PHOSPHORUS-METABOLISM OF A N-2-FIXING CYANOBACTERIUM ANABAENA-DOLIOLUM

This study demonstrated a general decrease in uptake of NH4+, urea and PO43-, activities of nitrogenase, glutamine synthetase, urease, alkal ine phosphatase and ATPase following ultraviolet-B (W-B) treatment and metal exposure, separately. As compared with an individual stressor t he effect of their combination was more detrimental to the above proce sses. In contrast, a significant increase in NO3- uptake and nitrate r eductase 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 respo nsible for uptake and assimilation of these nutrients. However, the me tals seem to compete for the binding sites of the above enzymes/carrie rs. A synergistic interaction of UV-B and metals (Cu/Pb) seems to be d ue to an increased metal uptake by an altered membrane permeability, a s a result of peroxidation of membrane lipids in UV-B exposed cells. ( C) 1998 Elsevier Science B.V. All rights reserved.