Structural and functional changes associated with heat‐induced phase‐separations of non‐bilayer lipids in chloroplast thylakoid membranes

Abstract

The effect of hearing isolated bean chloroplasts on the structure of their thylakoid membranes has been examined by freeze‐fracture electron microscopy. A normal morphology of the membranes in which stacked grana can be observed is preserved up to 35°C. Incubation at 35–45°C causes complete destacking of the grana but no alteration in the distribution of the membrane‐associated particles between the exoplasmic and protoplasmic fracture faces. Heating above 45°C causes phase‐separation of non‐bilayer lipids into aggregates of cylindrical inverted micelles. Bleaching experiments show that destacking is associated with disruption of chlorophyll‐protein complexes of both photosystems I and II. The rate of electron transport through the photosystems is also perturbed. These results are discussed in terms of the role of non‐bilayer lipids in packaging the membrane proteins.