Biosynthesis of grana and stroma lamellae in spinach.

Park and co-workers (Annu. Rev. Plant Physiol. 22: 395-430) have suggested that stroma lamellae, which perform only photosystem I contain a developing photosystem II which becomes functional upon the folding of these membranes to form grana stacks.The present study was undertaken to test this hypothesis. The lipid and protein constituents of chloroplast membranes were pulse-labeled radioactively with (14)C, and the specific activity of stroma and grana components were studied in a pulse-chase experiment. The components of both grana and stroma lamellae become labeled and decay at similar rates which suggests that the Park and Sane hypothesis is not correct. The results also show large differences in the turnover rates of some chloroplast membrane components supporting the multistep model for membrane synthesis and maintenance in this organelle.