Membrane Crystals of Plant Light-Harvesting Complex II Disassemble Reversibly in Light

Using the mass-measuring capability of scanning transmission electron microscopy, we demonstrate that membrane crystals of the main light-harvesting complex of plants possess the ability to undergo light-induced dark-reversible disassociations, independently of the photochemical apparatus. This is the first direct visualization of light-driven reversible reorganizations in an isolated photosynthetic antenna. These reorganizations, identified earlier by circular dichroism (CD), can be accounted for by a biological thermo-optic transition: structural changes are induced by fast heat transients and thermal instabilities near the dissipation, and self-association of the complexes in the lipid matrix. A comparable process in native membranes is indicated by earlier findings of essentially identical kinetics, and intensity and temperature dependences of the ΔCD in granal thylakoids.