Do glycerolipids display lateral heterogeneity in the thylakoid membrane?

The lateral heterogeneity of lipids in the thylakoid membrane has been ques tioned for over 20 yrs. It is generally believed that glycerolipids are asy mmetrically distributed within the plane of the membrane. In the present in vestigation, we isolated several thylakoid membrane domains by using sonica tion followed by separation in an aqueous dextran-polyethylene glycol two-p hase system. This technique, which avoids detergent treatments, allowed us to obtain stroma and grana lamellae vesicles as well as grana central core and grana margin vesicles from thylakoids, The relative distribution of the four lipid classes, i.e., monogalactosyldiacylglycerol, digalactosyldiacyl glycerol, sulfoquinovosyldiacylglycerol, and phosphatidylglycerol, was fou nd to be statistically identical in all four thylakoid fractions and in who le thylakoids. Similarly, the relative amount of fatty acids in each indivi dual lipid and the eight main phosphatidylglycerol molecular species was id entical in all thylakoid membrane fractions tested as well as in the intact thylakoid membrane. Based on presently available procedures for obtaining thylakoid subfractions that are unable to discriminate microdomains within the membrane, it is concluded that glycerolipids are evenly distributed wit hin the plane of the thylakoid membrane. These data are discussed in terms of "bulk" and "specific" lipids.