Chapter 14 Synthesis and Function of the Galactolipid Digalactosyldiacylglycerol

Abstract

Summary Seed plants contain two galactolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacyl­glycerol (DGDG) in their chloroplast membranes. DGDG is synthesized from UDP-galactose and MGDG by DGDG synthases in the envelope membranes of plastids. Galactolipids were identified in the X-ray structures of photosynthetic complexes. Deficiency of DGDG as observed in the dgd1 mutant of Arabidopsis has severe consequences for the efficiency of the photosynthetic machinery. The amount of DGDG increases when plants are grown under phosphate limitation. Under these conditions, DGDG serves as a surrogate for phospholipids thus saving phosphate for more important cellular processes. During senescence, chlorophyll and MGDG are degraded resulting in the release of free phytol and free fatty acids. At the same time, fatty acid phytyl esters accumulate in the plastoglobulies of chloroplasts. These esters serve as sink for the deposition of phytol and fatty acids which otherwise would destabilize the membrane bilayer structure.