Biosynthesis of Photosystem II Reaction Centers, Antenna and Plastoquinone Pool in Greening Cells of Cyanidium caldarium Mutant III-C.
Dark-grown etiolated cells of Cyanidium caldarium mutant III-C lacking >/=99% of their normal chlorophyll content and inactive for photosynthesis were greened in continuous light. Measurements of oxygen evolution and fluorescence kinetics indicate that during greening: (a) the photosystem II (PSII) antenna containing between 30 and 40 chlorophyll a per center undergoes little change in size from 5% of the centers synthesized per cell to fully active cells; (b) energy transfer between PSII centers appears very early in the greening process; (c) the plastoquinone pool size per PSII center (about 14 equivalents) does not vary during greening and has already attained full size after synthesis of only 13% of the full complement of centers.The PSII centers, antenna chlorophyll and plastoquinone are integrated into the membrane with constant stoichiometry throughout at least 90% of the greening process. These components are integrated such that in regions of the membrane containing active PSII centers, their density in the membrane hardly changes over the same period. The center-antenna complex and possibly the plastoquinone pool as well are organized into unit structures containing 40 chlorophyll a and 7 plastoquinones, respectively. Energy transfer between centers in PSII appears following aggregation of the center-antenna units.
Diner
B A
BA
Institut de Biologie Physico-Chimique, 13, rue Pierre et Marie Curie, 75005 Paris, France.
Wollman
F A
FA