ACTION OF SELECTED HEAVY-METAL IONS ON THE PHOTOSYSTEM-2 ACTIVITY OF THE CYANOBACTERIUM SPIRULINA-PLATENSIS

Addition of different concentrations of heavy metal ions (Hg2+, Cu2+, Ni2+ and Pb2+) inhibited the photosystem 2 catalyzed electron transpor t activity (H2O --> p-benzoquinone) of the cyanobacterium Spirulina pl atensis. Hg2+ caused the inhibition in electron transport activity in very low concentrations compared to the other metal ions. Hg2+ at this low concentration specifically altered the spectral properties of phy cocyanin of the phycobilisomes in the intact cells of Spirulina, where as other heavy metal ions were ineffective in this sense.