INTERACTIVE EFFECTS OF UV-B AND COPPER ON PHOTOSYNTHETIC ACTIVITY OF THE CYANOBACTERIUM ANABAENA-DOLIOLUM

This study presents information on the inhibition of carbon fixation, O2-evolution, photosynthetic electron transport chain, ATP pool and respiration rate of the cyanobacterium A. doliolum by UV-B and Cu. Interaction of UV-B (12.9 mWm-2 nm-1 for 12 and 25 min) and Cu2+ (0.3 and 0.5 mug ml-1) significantly increased the respiration rate and caused a shift from O2-evolution to O2-consumption. PSII exhibited the highest sensitivity to UV-B and Cu. A failure to restore DCPIP photoreduction by artificial electron donors (DPC, NH2OH and MnCl2) suggested that UV-B primarily inhibits the PSII reaction centre. Cu, however, reacts at multiple sites of the electron transport chain. The reduction and blue shifting of absorption peaks, suppression of fluorescence intensity and the excitation spectra indicate the involvement of phycobiliproteins in the inhibition of PSII activity. The synergistic interaction of UV-B and Cu appears due to increased Cu uptake brought about by an altered membrane permeability as a result of peroxidation of membrane lipids in the UV-B exposed cells.