Phase Transition Temperatures Determined for Chloroplast Thylakoid Membranes and for Liposomes Prepared from Charged Lipids Extracted from Thylakoid Membranes of Higher Plants

Lipid phase separation temperatures of intact thylakoid membranesfrom a number of chilling sensitive plants were measured usingchlorophyll a as the intrinsic fluorescent probe. The phospho-and sulfolipids were extracted from the thylakoid lamellae ofthese plants and purified by silicic acid column and thin layerchromatographies. These separated lipids were eluted and recombinedto give a total charged anionic thylakoid lipid fraction thatwas used to prepare liposomes containing purified chlorophylla as the fluorescent probe. The phase separation temperaturesof these liposomes were compared to phase separation temperaturesin intact thylakoid membranes isolated from the same plants. The chilling-sensitive plants—corn, pepper, tomato andwater hyacinth — showed phase separation temperaturesranging from 9 to 19°C for both the liposomes and the thylakoidmembranes. In addition, low temperature phase separations wereseen from –21 to –27°C. Mimulus, which is notas chilling sensitive as the former plants, had a phase separationtemperature near 0 to 2.5°C and at –27°C. In general,there was a good agreement between the phase separation temperaturesof intact thylakoids and the purified anionic lipid fractionextracted from these thylakoids. Similar results were obtained using either trans-parinaric acidor chlorophyll a as the fluorescent probe in liposomes madefrom anionic thylakoid lipids or in liposomes prepared frompure dimyristoyl phosphatidyl choline, distearoyl phosphatidylcholine, or mixtures of equal amounts of these phospholipids. ¹ CIW-DPB Publication # 728. ³ Present address: Laboratory of Experimental Physics, Departmentof Biophysics, State University of Utrecht, Princetonplein 5,Utrecht, The Netherlands. (Received January 18, 1981; Accepted July 2, 1981)