title: Interplay between non-photochemical plastoquinone reduction and re-oxidation in pre-illuminated Chlamydomonas reinhardtii: a chlorophyll fluorescence study.
abstract: In photosynthetic eukaryotes, the redox state of the plastoquinone (PQ) pool is an important sensor for mechanisms that regulate the photosynthetic electron transport. In higher plants, a multimeric nicotinamide adenine dinucleotide (phosphate) (NAD(P))H dehydrogenase (NDH) complex and a plastid terminal oxidase (PTOX) are involved in PQ redox homeostasis in the dark. We recently demonstrated that in the microalgae Chlamydomonas reinhardtii, which lacks the multimeric NDH complex of higher plants, non-photochemical PQ reduction is mediated by a monomeric type-II NDH (Nda2). In this study, we further explore the nature and the importance of non-photochemical PQ reduction and oxidation in relation to redox homeostasis in this alga by recording the 'dark' chlorophyll fluorescence transients of pre-illuminated algal samples. From the observation that this fluorescence transient is modified by addition of propyl gallate, a known inhibitor of PTOX, and in a Nda2-deficient strain we conclude that it reflects post-illumination changes in the redox state of PQ resulting from simultaneous PTOX and Nda2 activity. We show that the post-illumination fluorescence transient can be used to monitor changes in the relative rates of the non-photochemical PQ reduction and reoxidation in response to different physiological situations. We study this fluorescence transient in algae acclimated to high light and in a mutant deficient in mitochondrial respiration. Some of our observations indicate that the chlororespiratory pathway participates in redox homeostasis in C. reinhardtii.
authors.affiliation: Laboratory of Bioenergetics, Institute of Plant Biology B22, University of Liège, Sart Tilman, 4000 Liège, Belgium.
authors.forename: Pierre-Alain
authors.initials: PA
authors.lastname: Houyoux
authors.forename: Bart
authors.initials: B
authors.lastname: Ghysels
authors.forename: Renaud
authors.initials: R
authors.lastname: Lecler
authors.forename: Fabrice
authors.initials: F
authors.lastname: Franck
mesh_terms: D019069:Cell Respiration; D016825:Chlamydomonas reinhardtii / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D003624:Darkness; D004579:Electron Transport; D005453:Fluorescence; D008027:Light; D008928:Mitochondria / Q000378:metabolism; D009154:Mutation; D009249:NADP / Q000378:metabolism*; D009252:NADPH Dehydrogenase / Q000378:metabolism; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D010100:Oxygen / Q000378:metabolism; D055668:Photochemical Processes; D010788:Photosynthesis / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism*; D010971:Plastoquinone / Q000378:metabolism*; D011435:Propyl Gallate / Q000494:pharmacology
chemical_list: D010940:Plant Proteins; D002734:Chlorophyll; D009249:NADP; D011435:Propyl Gallate; D009252:NADPH Dehydrogenase; D010971:Plastoquinone; D010100:Oxygen