INTERACTIONS OF ARBUTIN WITH DRY AND HYDRATED BILAYERS

The glycosylated hydroquinone arbutin (4-hydroxyphenyl-beta-D-glucopyr anoside) is abundant in certain resurrection plants, which can survive almost complete dehydration for prolonged periods. Little is known ab out the role of arbutin in vivo, but it is thought to contribute towar d survival of the plants in the dry state. We have investigated the in teractions of arbutin with model membranes under conditions of high an d low hydration, as well as the possible participation of arbutin in c arbohydrate glasses formed at low water contents. Retention of a trapp ed soluble marker inside large unilamellar vesicles and fusion of vesi cles was monitored by fluorescence spectroscopy. Effects of arbutin on glass-transition temperatures and hydrated membrane phase-transition temperatures were measured by differential scanning calorimetry. The p ossible insertion of arbutin into membrane bilayers was estimated by f ollowing arbutin auto-fluorescence. Evidence is presented that arbutin does not change the glass-transition temperature of a sucrose/trehalo se glass, but that arbutin does interact with hydrated membranes by in sertion of the phenol moiety into the lipid bilayer. This interaction causes increased membrane leakage during air-drying by a mechanism oth er than vesicle-vesicle fusion. Implications of these effects on the d ehydrated plant cells, as well as possible methods of obviating the da mage, are discussed. (C) 1998 Elsevier Science B.V.