Functional and Structural Organization of Chlorophyll in the Developing Photosynthetic Membranes of Euglena gracilis Z: II. CHARACTERISTICS OF THE LATE FORMATION OF ACTIVE PHOTOSYSTEM II REACTION CENTERS DURING FIRST STAGES OF GREENING.
During light-induced greening of dark-grown, nondividing Euglena gracilis Z, there is a delay of about 10 hours in the formation of active photosystem II (PSII) reaction centers compared to chlorophyll synthesis. Experiments with greening under different light intensities rule out the possibility that this delay results from a late induction of active PSII reaction center formation when a definite amount of chlorophyll is attained in the early greened cells. Experiments on greening after preillumination show that this delay does not originate in a long, light-induced formation of specific synthesizing machinery for reaction center components. Experiments with greening in the presence of streptomycin show that, when this inhibitor of protein synthesis by chloroplastic ribosomes is added to dark-grown, preilluminated cells or to cells already greened for 24 hours, the formation of active PSII reaction centers is inhibited after a time which depends on the light intensity used for greening. Under very low light intensity (150 lux), the addition of streptomycin to 24-hour greened cells does not prevent further development of functional chloroplasts. These observations lead to the conclusion that streptomycin-insensitive chloro-plast development occurs due to syntheses of cytoplasmic origin and of light-induced pools of components synthesized early by chloroplastic ribo-somes. Conformational changes requiring time may allow the insertion of components necessary for the reorganization of PSII reaction centers in the developing thylakoid after synthesis. This hypothesis accounts for the observed delay in PSII reaction center formation compared to chlorophyll synthesis.
Dubertret
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Cytophysiologie de la Photosynthèse, Centre National de la Recherche Scientifique, Gif sur Yvette, France, 91190.
Ambard-Bretteville
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