Abstract
In plant chloroplasts and cyanobacteria, glycerolipids that carry galactose in their head group are the predominant lipid components of the membranes whereas mostly phospholipids are the most abundant polar lipid class in the membranes of other organisms. Because of their abundance in the photosynthetic membranes, the importance of these galactolipids in photosynthesis has been suggested. Since the enzymes that catalyze the syntheses of these galactolipids were identified, significant progress has been achieved in the elucidation and understanding of the biosynthetic pathways and their regulatory mechanisms. In addition, genetic and reverse-genetic approaches in these enzymes revealed physiological roles of galactolipids in photosynthesis and adaptation systems to several stresses. In photosynthetic tissues, galactolipids are indispensable for thylakoid membrane biogenesis and are directly involved in the photosynthetic reactions. Moreover, galactolipids are required for membrane maintenance during phosphate deficiency by substituting phospholipids in plastidic and extraplastidic membranes. The regulatory mechanisms for galactolipid biosyntheses upon photomorphogenesis and stress conditions have also been studied in transcription levels and enzymatic activity levels.
