From chloroplasts to photosystems: in situ scanning force microscopy on intact thylakoid membranes.
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.
Kaftan
David
D
Department of Plant Sciences and Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
Brumfeld
Vlad
V
Nevo
Reinat
R
Scherz
Avigdor
A
Reich
Ziv
Z
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*
D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D025222:Chloroplast Proton-Translocating ATPases