title: Involvement of a plastid terminal oxidase in plastoquinone oxidation as evidenced by expression of the Arabidopsis thaliana enzyme in tobacco.
abstract: Chlororespiration has been defined as a respiratory electron transport chain in interaction with photosynthetic electron transport involving both non-photochemical reduction and oxidation of plastoquinones. Different enzymatic activities, including a plastid-encoded NADH dehydrogenase complex, have been reported to be involved in the non-photochemical reduction of plastoquinones. However, the enzyme responsible for plasquinol oxidation has not yet been clearly identified. In order to determine whether the newly discovered plastid oxidase (PTOX) involved in carotenoid biosynthesis acts as a plastoquinol oxidase in higher plant chloroplasts, the Arabidopsis thaliana PTOX gene (At-PTOX) was expressed in tobacco under the control of a strong constitutive promoter. We showed that At-PTOX is functional in tobacco chloroplasts and strongly accelerates the non-photochemical reoxidation of plastoquinols; this effect was inhibited by propyl gallate, a known inhibitor of PTOX. During the dark to light induction phase of photosynthesis at low irradiances, At-PTOX drives significant electron flow to O(2), thus avoiding over-reduction of plastoquinones, when photo- synthetic CO(2) assimilation was not fully induced. We proposed that PTOX, by modulating the redox state of intersystem electron carriers, may participate in the regulation of cyclic electron flow around photosystem I.
authors.affiliation: CEA Cadarache, Direction des Sciences du Vivant, Département d'Ecophysiologie Végétale et de Microbiologie, Laboratoire d'Ecophysiologie de la Photosynthèse, Unité Mixte de Recherche 163 CNRS CEA, Univ-Mediterranée CEA1000, Saint-Paul-lez-Durance, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Joët
authors.forename: Bernard
authors.initials: B
authors.lastname: Genty
authors.forename: Eve-Marie
authors.initials: EM
authors.lastname: Josse
authors.forename: Marcel
authors.initials: M
authors.lastname: Kuntz
authors.forename: Laurent
authors.initials: L
authors.lastname: Cournac
authors.forename: Gilles
authors.initials: G
authors.lastname: Peltier
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D017931:DNA Primers; D007700:Kinetics; D008027:Light; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D018087:Plastids / Q000201:enzymology*; D010971:Plastoquinone / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D013050:Spectrometry, Fluorescence; D014026:Nicotiana / Q000201:enzymology*; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D002734:Chlorophyll; D017931:DNA Primers; D009243:NAD; D010088:Oxidoreductases; D010971:Plastoquinone; C405742:IM protein, Arabidopsis