Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the two nonionic lipid constituents of the thylakoid membrane of higher plant chloroplasts. MGDG and DGDG are present in the membrane at 56% and 29%, respectively, of the total lipid content. DGDG is a bilayer-forming lipid, while MGDG alone will only form hexagonal-II structures.