Atomic Force Microscopy Captures Light-Induced Higher-Order Structural Dynamics in Photosystem II Supercomplexes

The photosystem II (PSII)-light-harvesting complex II (LHCII) supercomplex within plant thylakoid membranes plays a central role in photosynthesis. Multiple PSII-LHCII supercomplexes within the thylakoid membranes assemble into higher-order supramolecular structures in response to environmental light conditions. In this study, we used high-speed atomic force microscopy (AFM) to visualize isolated thylakoid membranes. This enabled the observation of PSII-LHCII supercomplexes in a physiologically relevant environment. AFM imaging and biochemical analyses revealed disrupted semicrystalline-array-like PSII-LHCII assemblies under high-light acclimation. Detailed image analysis, combined with three-dimensional PSII model fitting, revealed two distinct configurations of the semicrystalline arrays: parallel and offset. Although the parallel array remained stable, the offset array was destabilized in a PsbS-dependent manner under high-light acclimation. These findings demonstrate that high-light acclimation and PsbS correlate with PSII-LHCII supercomplex organization in isolated membranes.