Temperature-Dependent Phase Behavior of Phosphatidylglycerols from Chilling-Sensitive and Chilling-Resistant Plants

Seven major lipid classes were isolated from leaves of chilling-sensitive and chilling-resistant plants, and the temperature-dependent phase behaviors of their aqueous dispersions were studied by a fluorescence polarization method using trans-parinaric acid and its methyl ester. Phosphatidylglycerols from the chilling-sensitive plants went from the liquid crystalline state into the phase separation state at about 30 degrees C in 100 mm NaCl and at about 40 degrees C in 5 mm MgCl(2). In contrast, phosphatidylglycerols from the chilling-resistant plants went into the phase separation state at a much lower temperature. The other classes of lipids remained in the liquid crystalline state at all temperatures between 5 degrees C and 40 degrees C regardless of the chilling sensitivity of the plants, except sulfoquinovosyl diacylglycerol from sponge cucumber in which phase separation seemed to begin at about 15 degrees C. Compositions and positional distributions of fatty acids of the lipids suggest that the phosphatidylglycerols from the chilling-sensitive plants, but no other lipids, contained large proportions of molecular species which undergo phase transition at room temperature or above. The thermotropic phase behaviors and the fatty acid compositions suggest that, among the major lipid classes from leaves of the chilling-sensitive plants, only phosphatidylglycerol can induce a phase transition. Since a major part of this lipid in leaves originates from the chloroplasts, phase transition probably occurs in the chloroplast membranes.