Chloroplast Protein Synthesis in the Chromophytic Alga Olisthodiscus luteus: Cell Cycle Analysis.

This study represents the first report on chloroplast protein synthesis during the synchronous cell growth of a chromophytic (chlorophyll a,c) plant. When the unicellular alga Olisthodiscus luteus is maintained on a 12-hour light:12-hour dark cycle, cell and chloroplast number double every 24 hours. A temporal separation between these two events occurs. Measurements of chloroplast and total cellular protein values suggest that polypeptide synthesis occurs mainly in the light portion of the cell cycle, and pulse chase studies demonstrate that chloroplast proteins made in the light are not degraded in the dark. Data support the following conclusions: (a) a similar complement of chloroplast DNA coded proteins is made at all phases of the light portion of the cell cycle, and (b) chloroplast protein synthesis is a light rather than a cell cycle mediated response.