Phase Transition Temperatures Determined for Chloroplast Thylakoid Membranes and for Liposomes Prepared from Charged Lipids Extracted from Thylakoid Membranes of Higher Plants<xref ref-type="fn" rid="fn1"><sup>1</sup></xref>

Abstract

Lipid phase separation temperatures of intact thylakoid membranes from a number of chilling sensitive plants were measured using chlorophyll a as the intrinsic fluorescent probe. The phospho- and sulfolipids were extracted from the thylakoid lamellae of these plants and purified by silicic acid column and thin layer chromatographies. These separated lipids were eluted and recombined to give a total charged anionic thylakoid lipid fraction that was used to prepare liposomes containing purified chlorophyll a as the fluorescent probe. The phase separation temperatures of these liposomes were compared to phase separation temperatures in intact thylakoid membranes isolated from the same plants. The chilling-sensitive plants—corn, pepper, tomato and water hyacinth — showed phase separation temperatures ranging from 9 to 19°C for both the liposomes and the thylakoid membranes. In addition, low temperature phase separations were seen from −21 to −27°C. Mimulus, which is not as chilling sensitive as the former plants, had a phase separation temperature near 0 to 2.5°C and at −27°C. In general, there was a good agreement between the phase separation temperatures of intact thylakoids and the purified anionic lipid fraction extracted from these thylakoids. Similar results were obtained using either trans-parinaric acid or chlorophyll a as the fluorescent probe in liposomes made from anionic thylakoid lipids or in liposomes prepared from pure dimyristoyl phosphatidyl choline, distearoyl phosphatidyl choline, or mixtures of equal amounts of these phospholipids.