Response of intact cyanobacterial cells and their photosynthetic apparatus to Cd2+ ion treatment

Intact cells of Synechococcus elongatus were treated with different concentrations (0.1 and 1.0 mM = Cd-0.1, Cd-1.0) of CdCl2 for 24 h. Cd-0.1 treatment stimulated growth of the cell culture and chlorophyll (Chl) a concentration in the culture. Cd-1.0 inhibited both the above mentioned parameters. The oxygen evolving activity of intact cells (H2O --> BQ) as well as of isolated thylakoid membranes, TM (H2O --> DCPIP; H2O --> PBQ + FeCy) decreased after 24 h of Cd-1.0 cultivation to 7 %. Photosystem 1 (PS1) activity was less sensitive to the effect of Cd2+ than PS2 activity. CdCl2 concentration in cultivation media after 24 h of cultivation proved that the cyanobacterium cells take up these ions to a large extent from the cultivation medium. After 24 h of the Cd-1.0 treatment only 12 % of the amount of Cd2+ originally added to the cultivation medium was found. The ratio of external-antenna pigments, phycocyanin, and allophycocyanin to Chl increased approximately twofold with growing Cd2+ concentration in the cultivation medium. This ratio was found in both TM and dodecylmaltoside extracts.