Fig. 3.

The prokaryotic pathway of lipid synthesis is suppressed in guard cells. (A and B) Chloroplast polar lipid species were determined in guard cell protoplasts GCPs and MCPs, which were isolated from WT and gles1 mutants. As an overview, we have depicted representatives of the most abundant species derived from the eukaryotic pathway (A) or prokaryotic pathway (B). MGDG, DGDG, and PG content are shown. Values shown are means ± SE (n = 4). The statistical significance was determined by a one-way ANOVA with Tukey-Kramer multiple comparison tests. Same letters (a–c) indicate no significant difference (P > 0.05). A complete dataset with details on analysis is given in SI Appendix, Fig. S6. (C) Schematic diagram of deduced lipid flux model in Arabidopsis mesophyll cells and guard cells. We propose that the contribution of the prokaryotic and eukaryotic lipid pathways is different between mesophyll cells and guard cells, and that the guard cells rely on the eukaryotic pathway exclusively. Therefore, the ER-to-plastid lipid trafficking mediated by the TGD complex is essential for the formation of guard cell chloroplasts. FA, fatty acid; PE, phosphatidylethanolamine.