THE PIGMENT-PROTEIN COMPLEXES OF PHOTOSYNTHETIC MEMBRANES OF THE CYANOBACTERIUM SYNECHOCYSTIS SP THE EFFECT OF IRON-DEFICIENCY

The effect of accumulation of the pigment complex CP36 on the ratio be tween pigment-protein complexes was studied under various cultivation conditions of Synechocystis sp. PCC, 6803, wild type, and mutants Delt a-2 (lacking PS2) and Delta-3 (lacking PS1); Synechocystis sp. BO 8402 (lacking phycobilisomes) and BO 9201 (a derivative of 8402 strain wit h phycobilisomes). The concentration of iron in the medium determines the content of CP36, which does not depend on the intensity of illumin ation during growth. Strain 8402 compensates the deficit of light-harv esting antenna of PS2 by synthesizing large amounts of PS2 complex. Un der conditions of moderate iron deficiency the studied strains includi ng mutants that do not contain one of the photosystems accumulate CP36 ; a sole exception was BO 8402. The content of phycobiliproteins was n ot decreased and the concentrations of both photosystems decreased pro portionally. The content of PS2 monomers per phycobilisome decreased f rom 2-3 to 1. CP36 effectively transfers the electron excitation energ y to both photosystems but it is predominantly connected with photosys tem 2. This suggests that CP36 can stabilize the PS2 complex and can b e an evolutionary precursor of the light-harvesting structures of high er plants.