title: Chloroplast thylakoid membrane fluidity and its sensitivity to temperature.
abstract: In order to investigate membrane fluidity, the hydrophobic probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), has been incorporated into intact isolated thylakoids and separated granal and stromal lamellae obtained from the chloroplasts of Pisum sativum. The steady-state polarization of DPH fluorescence was measured as a function of temperature and indicated that at physiological values the thylakoid membrane is a relatively fluid system with the stromal lamellae being less viscous than the lamellae of the grana. According to the DPH technique, neither region of the membrane, however, showed a sharp phase transition of its bulk lipids from the liquid-crystalline to the gel state for the temperature range -20° to 50° C. Comparison of intact thylakoids isolated from plants grown at cold (4°/7°C) and warm (14°/17° C) temperatures indicate that there is an adaptation mechanism operating which seems to maintain an optimal membrane viscosity necessary for growth. Using a modified Perrin equation the optimal average viscosity for the thylakoid membrane of the chill-resistant variety used in the study (Feltham First) is estimated to be about 1.8 poise.
authors.affiliation: AFRC Photosynthesis Research Group, Department of Pure and Applied Biology, Imperial College of Science and Technology, SW7 2BB, London, UK.
authors.forename: J
authors.initials: J
authors.lastname: Barber
authors.forename: R C
authors.initials: RC
authors.lastname: Ford
authors.forename: R A
authors.initials: RA
authors.lastname: Mitchell
authors.forename: P A
authors.initials: PA
authors.lastname: Millner