Cd2+ effect on photosynthetic apparatus in Synechococcus elongatus and spinach (Spinacia oleracea L.)

Thylakoid membranes (TM) of the cyanobacterium Synechococcus elongatus were exposed for 30 min to the influence of 0, 10, 100, and 1 000 mM CdCl2 (= Cd-0, Cd-10, Cd-100, and Cd-1000). Cd-10 and Cd-100 caused some increase in activity of photosystem 2, PS2 (H2O --> DCPIP), while distinct inhibition was observed with Cd-1000. We also observed a similar effect when measuring oxygen evolution (H2O --> PBQ + FeCy). Chloroplasts of spinach (Spinacia oleracea L.) were incubated for 30 min with 0, 15, 30, and 60 mM CdCl2 (= Cd-0, Cd-15, Cd-30, and Cd-60). All concentrations studied inhibited the PS2 activity, the effect being stronger with increasing concentration of Cd2+. The photosynthetic oxygen evolution activity was also influenced most distinctly by the highest concentration employed, i.e. Cd-60. Electrophoretic analysis of the protein composition of cyanobacterium TM showed chief changes in the molecular mass regions of M, 29 000 and 116 000, while with spinach chloroplasts the most distinct differences were observed in the regions of M, 15 000 and 50 000. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity in cyanobacterial spheroplasts still remained on the 40% level in the case of Cd-1000, but it decreased down to approx. 2.5% in the Cd-60 sample of spinach chloroplasts.