TREHALOSE INCREASES FREEZE-THAW DAMAGE IN LIPOSOMES CONTAINING CHLOROPLAST GLYCOLIPIDS

Chloroplast thylakoids contain three classes of glycolipids, monogalac tosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sul foquinovosyldiacylglycerol (SQDG). We have investigated the stability of large unilamellar vesicles made from egg phosphatidylcholine (EPC) and different chloroplast glycolipids during freezing to -18 degrees C , as a function of the presence of three sugars: glucose, sucrose, or trehalose. Contrary to the situation in thylakoids, where cryoprotecti on increases from glucose < sucrose < trehalose, liposomes containing 50% DGDG showed the opposite behavior. In fact, carboxyfluorescein lea kage increased over the control values (freezing in the absence of sug ar) in the presence of trehalose. This effect was not seen in vesicles made from pure EPC, or a mixture of EPC and MGDG, or EPC and SQDG. Li posomes made from mixtures of all three glycolipids, however, showed e ven more leakage in the presence of trehalose than liposomes containin g only DGDG and EPC. (C) 1998 Academic Press.