title: Action spectrum of photoinhibition in leaves of wild type and npq1-2 and npq4-1 mutants of Arabidopsis thaliana.
abstract: Photoinhibition is light-induced inactivation of PSII. Hypotheses about the photoreceptor(s) of photoinhibition include the Chl antenna of PSII, manganese of the oxygen-evolving complex (OEC), uncoupled Chl and iron-sulfur centres. We measured the action spectrum of photoinhibition in vivo from wild-type Arabidopsis thaliana L. and from the npq1-2 and npq4-1 mutants defective in non-photochemical quenching (NPQ) of excitations of the PSII antenna. The in vivo action spectrum was found to resemble closely the in vitro action spectra published for photoinhibition. We compared the action spectrum with absorbance spectra of model compounds of the OEC complex and other potential photoreceptors of photoinhibition. The comparison suggests that both manganese and Chl function as photoreceptors in photoinhibition. In accordance with the function of two types of photoreceptors in photoinhibition, NPQ was found to offer only partial protection against photoinhibition at visible wavelengths. The low protective efficiency of NPQ supports the conclusion that the Chl antenna of PSII is not the only photoreceptor of photoinhibition. Comparison of the action spectrum of photoinhibition with the emission spectrum of sunlight shows that the UV part of sunlight is responsible for the major part of photoinhibition under natural conditions.
authors.affiliation: Plant Physiology and Molecular Biology, Department of Biology, University of Turku, Finland.
authors.forename: Päivi
authors.initials: P
authors.lastname: Sarvikas
authors.forename: Marja
authors.initials: M
authors.lastname: Hakala
authors.forename: Eija
authors.initials: E
authors.lastname: Pätsikkä
authors.forename: Taina
authors.initials: T
authors.lastname: Tyystjärvi
authors.forename: Esa
authors.initials: E
authors.lastname: Tyystjärvi
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D004579:Electron Transport / Q000528:radiation effects; D005453:Fluorescence; D045342:Light-Harvesting Protein Complexes; D009154:Mutation / Q000235:genetics*; D010786:Photoreceptor Cells / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D018515:Plant Leaves / Q000235:genetics / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; C489731:NPQ4 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll