Chuartzman, S.G., Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
Nevo, R., Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
Shimoni, E., Electron Microscopy Unit, Weizmann Institute of Science, Rehovot 76100, Israel
Charuvi, D., Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel, Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel
Kiss, V., Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
Ohad, I., Institute of Life Sciences, Avron-Even-Ari Minerva Center for Photosynthesis Research, Hebrew University of Jerusalem, Jerusalem 91014, Israel
Brumfeld, V., Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
Reicha, Z., Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel

Adaptability of oxygenic photosynthetic organisms to fluctuations in light spectral composition and intensity is conferred by state transitions, short-term regulatory processes that enable the photosynthetic apparatus to rapidly adjust to variations in light quality. In green algae and higher plants, these processes are accompanied by reversible structural rearrangements in the thylakoid membranes. We studied these structural changes in the thylakoid membranes of Arabidopsis thaliana chloroplasts using atomic force microscopy, scanning and transmission electron microscopy, and confocal imaging. Based on our results and on the recently determined three-dimensional structure of higher-plant thylakoids trapped in one of the two major light-adapted states, we propose a model for the transitions in membrane architecture. The model suggests that reorganization of the membranes involves fission and fusion events that occur at the interface between the appressed (granal) and nonappressed (stroma lamellar) domains of the thylakoid membranes. Vertical and lateral displacements of the grana layers presumably follow these localized events, eventually leading to macroscopic rearrangements of the entire membrane network. © 2008 American Society of Plant Biologists.