EFFECT OF COBALT IONS ON THE DELAYED AND PROMPT LUMINESCENCE IN PEA-CHLOROPLASTS

The millisecond delayed luminescence in chloroplasts of pea (Pisum sat ivum L.) is quenched by Co2+ ions added as CoSO4 or CoCl2. The extent of quenching increased with Co2+ concentration and was independent of the presence of DCMU. The effect of Co2+ on the delayed luminescence a ppeared immediately after adding Co2+, and it was removed by washing t he chloroplast preparations or by lowering the external pH to 5.5. Mea surements of prompt chlorophyll luminescence in the presence of MgCl2 revealed similar, although somewhat weaker inhibition of light emissio n by Co2+. However, adding Co2+ to the MgCl2-free medium stimulated th e low yield of prompt chlorophyll luminescence. These results suggest that effects of Co2+ On the chloroplast luminescence are mediated by e lectrostatic interactions of Co2+ With exposed polar groups in protein s constituting the light-harvesting complex or transferring electrons between P680 and Q(A) in photosystem II.