title: From chloroplasts to photosystems: in situ scanning force microscopy on intact thylakoid membranes.
abstract: Envelope-free chloroplasts were imaged in situ by contact and tapping mode scanning force microscopy at a lateral resolution of 3-5 nm and vertical resolution of approximately 0.3 nm. The images of the intact thylakoids revealed detailed structural features of their surface, including individual protein complexes over stroma, grana margin and grana-end membrane domains. Structural and immunogold-assisted assignment of two of these complexes, photosystem I (PS I) and ATP synthase, allowed direct determination of their surface density, which, for both, was found to be highest in grana margins. Surface rearrangements and pigment- protein complex redistribution associated with salt-induced membrane unstacking were followed on native, hydrated specimens. Unstacking was accompanied by a substantial increase in grana diameter and, eventually, led to their merging with the stroma lamellae. Concomitantly, PS IIalpha effective antenna size decreased by 21% and the mean size of membrane particles increased substantially, consistent with attachment of mobile light-harvesting complex II to PS I. The ability to image intact photosynthetic membranes at molecular resolution, as demonstrated here, opens up new vistas to investigate thylakoid structure and function.
authors.affiliation: Department of Plant Sciences and Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Kaftan
authors.forename: Vlad
authors.initials: V
authors.lastname: Brumfeld
authors.forename: Reinat
authors.initials: R
authors.lastname: Nevo
authors.forename: Avigdor
authors.initials: A
authors.lastname: Scherz
authors.forename: Ziv
authors.initials: Z
authors.lastname: Reich
mesh_terms: D025222:Chloroplast Proton-Translocating ATPases / Q000648:ultrastructure; D021621:Imaging, Three-Dimensional; D007150:Immunohistochemistry; D007425:Intracellular Membranes / Q000648:ultrastructure*; D018545:Lactuca; D018625:Microscopy, Atomic Force; D008854:Microscopy, Electron; D010316:Particle Size; D045322:Photosynthetic Reaction Center Complex Proteins / Q000648:ultrastructure*; D045331:Photosystem I Protein Complex; D020524:Thylakoids / Q000648:ultrastructure*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D025222:Chloroplast Proton-Translocating ATPases