title: Photoprotective energy dissipation involves the reorganization of photosystem II light-harvesting complexes in the grana membranes of spinach chloroplasts.
abstract: Plants must regulate their use of absorbed light energy on a minute-by-minute basis to maximize the efficiency of photosynthesis and to protect photosystem II (PSII) reaction centers from photooxidative damage. The regulation of light harvesting involves the photoprotective dissipation of excess absorbed light energy in the light-harvesting antenna complexes (LHCs) as heat. Here, we report an investigation into the structural basis of light-harvesting regulation in intact spinach (Spinacia oleracea) chloroplasts using freeze-fracture electron microscopy, combined with laser confocal microscopy employing the fluorescence recovery after photobleaching technique. The results demonstrate that formation of the photoprotective state requires a structural reorganization of the photosynthetic membrane involving dissociation of LHCII from PSII and its aggregation. The structural changes are manifested by a reduced mobility of LHC antenna chlorophyll proteins. It is demonstrated that these changes occur rapidly and reversibly within 5 min of illumination and dark relaxation, are dependent on ΔpH, and are enhanced by the deepoxidation of violaxanthin to zeaxanthin.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London E14NS, United Kingdom.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Johnson
authors.forename: Tomasz K
authors.initials: TK
authors.lastname: Goral
authors.forename: Christopher D P
authors.initials: CD
authors.lastname: Duffy
authors.forename: Anthony P R
authors.initials: AP
authors.lastname: Brain
authors.forename: Conrad W
authors.initials: CW
authors.lastname: Mullineaux
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Ruban
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D036681:Fluorescence Recovery After Photobleaching; D005614:Freeze Fracturing; D007425:Intracellular Membranes / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D008958:Models, Molecular; D055668:Photochemical Processes; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D021381:Protein Transport; D018724:Spinacia oleracea / Q000378:metabolism* / Q000648:ultrastructure; D013816:Thermodynamics; D020524:Thylakoids / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll