Relationship between Thylakoid Membrane Fluidity and the Kinetics of Salt Induced Fluorescence Changes: a Spin Label Study

Abstract

Stacking of thylakoid membranes leads to the separation of Photosystem II and Photosystem I into appressed and non-appressed membrane regions. The associated increase in chlorophyll fluorescence is currently believed to reflect a decrease in spillover of exitation energy from Photosystem II to Photosystem I (Barber, 1980). Following kinetic analysis it has been suggested that the process can be interpreted in terms of a diffusion-limited movement of Photosystem II complexes (Rubin et al., 1981; Jennings et al., 1982). Lateral diffusion of large protein complexes in a biological membrane is highly dependent on physico-chemical parameters such as membrane fluidity. We have altered the thylakoid membrane composition artificially in order to change the membrane fluidity and observed the corresponding changes in the salt induced fluorescence rise. Thylakoids were rigidified by incorporation of cholesteryl hemisuccinate and the local anaesthetic benzyl alcohol was used as membrane fluidising agent.