title: Differential mobility of pigment-protein complexes in granal and agranal thylakoid membranes of C₃ and C₄ plants.
abstract: The photosynthetic performance of plants is crucially dependent on the mobility of the molecular complexes that catalyze the conversion of sunlight to metabolic energy equivalents in the thylakoid membrane network inside chloroplasts. The role of the extensive folding of thylakoid membranes leading to structural differentiation into stacked grana regions and unstacked stroma lamellae for diffusion-based processes of the photosynthetic machinery is poorly understood. This study examines, to our knowledge for the first time, the mobility of photosynthetic pigment-protein complexes in unstacked thylakoid regions in the C₃ plant Arabidopsis (Arabidopsis thaliana) and agranal bundle sheath chloroplasts of the C₄ plants sorghum (Sorghum bicolor) and maize (Zea mays) by the fluorescence recovery after photobleaching technique. In unstacked thylakoid membranes, more than 50% of the protein complexes are mobile, whereas this number drops to about 20% in stacked grana regions. The higher molecular mobility in unstacked thylakoid regions is explained by a lower protein-packing density compared with stacked grana regions. It is postulated that thylakoid membrane stacking to form grana leads to protein crowding that impedes lateral diffusion processes but is required for efficient light harvesting of the modularly organized photosystem II and its light-harvesting antenna system. In contrast, the arrangement of the photosystem I light-harvesting complex I in separate units in unstacked thylakoid membranes does not require dense protein packing, which is advantageous for protein diffusion.
authors.affiliation: Institute of Biological Chemistry , Washington State University, Pullman, Washington 99164, USA. kirchhh@wsu.edu
authors.forename: Helmut
authors.initials: H
authors.lastname: Kirchhoff
authors.forename: Richard M
authors.initials: RM
authors.lastname: Sharpe
authors.forename: Miroslava
authors.initials: M
authors.lastname: Herbstova
authors.forename: Robert
authors.initials: R
authors.lastname: Yarbrough
authors.forename: Gerald E
authors.initials: GE
authors.lastname: Edwards
mesh_terms: D017360:Arabidopsis / Q000378:metabolism* / Q000502:physiology; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D004058:Diffusion; D004591:Electrophoresis, Polyacrylamide Gel; D036681:Fluorescence Recovery After Photobleaching; D008027:Light; D008563:Membrane Lipids / Q000378:metabolism; D058503:Mesophyll Cells / Q000378:metabolism; D018613:Microscopy, Confocal; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology; D021381:Protein Transport; D011523:Protoplasts / Q000378:metabolism; D045868:Sorghum / Q000378:metabolism / Q000502:physiology; D013045:Species Specificity; D020524:Thylakoids / Q000378:metabolism* / Q000502:physiology; D003313:Zea mays / Q000378:metabolism / Q000502:physiology
chemical_list: D008563:Membrane Lipids; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D000077194:Chlorophyll A