Moleculaar-biological analysis of function of chloroplast membrane lopids in highr plants

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Phosphatidylglycerol (PG) is a ubiquitous phospholipid in the biological membranes of many organisms. In plants, PG is mainly present in chloroplasts and has been suggested to play specific roles in photosynthesis. However, the specific roles of PG in chloroplasts have not been well understood. In this study, we have investigated the roles of PG in chloroplasts with two T-DNA tagged lines of Arabidopsis thaliana that have a T-DNA insertion in the PGP1 gene encoding a PG phosphate synthase involved in the biosynthesis of PG in chloroplasts. In homozygous plants of the T-DNA tagged lines, the PGP1 gene was completely disrupted. The growth of these knockout mutants was dependent on the presence of sucrose in the growth medium, and these plants had pale yellow-green leaves. The leaves of the mutants had remarkably large intercellular spaces due to the reduction in the number of mesophyll cells. The development of chloroplasts in the leaf cells was severely arrested in the mutants. Mesophyll cells with chloroplast particles are only found around vascular structures, whereas epidermal cells are enlarged but largely conserved. The content of PG in ghe mutants was reduced to 12% of the of the wild type. These results demonstrate that pg is essential for the development of thylakoid membranes In A.thaliana.