title: Ascorbate accumulation during sulphur deprivation and its effects on photosystem II activity and H2 production of the green alga Chlamydomonas reinhardtii.
abstract: In nature, H2 production in Chlamydomonas reinhardtii serves as a safety valve during the induction of photosynthesis in anoxia, and it prevents the over-reduction of the photosynthetic electron transport chain. Sulphur deprivation of C. reinhardtii also triggers a complex metabolic response resulting in the induction of various stress-related genes, down-regulation of photosynthesis, the establishment of anaerobiosis and expression of active hydrogenase. Photosystem II (PSII) plays dual role in H2 production because it supplies electrons but the evolved O2 inhibits the hydrogenase. Here, we show that upon sulphur deprivation, the ascorbate content in C. reinhardtii increases about 50-fold, reaching the mM range; at this concentration, ascorbate inactivates the Mn-cluster of PSII, and afterwards, it can donate electrons to tyrozin Z(+) at a slow rate. This stage is followed by donor-side-induced photoinhibition, leading to the loss of charge separation activity in PSII and reaction centre degradation. The time point at which maximum ascorbate concentration is reached in the cell is critical for the establishment of anaerobiosis and initiation of H2 production. We also show that ascorbate influenced H2 evolution via altering the photosynthetic electron transport rather than hydrogenase activity and starch degradation.
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: Valéria
authors.initials: V
authors.lastname: Nagy
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: André
authors.initials: A
authors.lastname: Vidal-Meireles
authors.affiliation: Department of Biotechnology, University of Szeged, Közép fasor 52, H-6726, Szeged, Hungary.
authors.forename: Roland
authors.initials: R
authors.lastname: Tengölics
authors.affiliation: Department of Biotechnology, University of Szeged, Közép fasor 52, H-6726, Szeged, Hungary.|Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Rákhely
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: Győző
authors.initials: G
authors.lastname: Garab
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Kovács
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Temesvári krt. 62, H-6726, Szeged, Hungary.
authors.forename: Szilvia Z
authors.initials: SZ
authors.lastname: Tóth
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D013213:Starch / Q000378:metabolism; D013455:Sulfur / Q000172:deficiency*
chemical_list: D045332:Photosystem II Protein Complex; D013455:Sulfur; D006859:Hydrogen; D013213:Starch; D006864:Hydrogenase; D001205:Ascorbic Acid
keywords: chlorophyll a fluorescence; hydrogenase; oxygen evolution; thermoluminescence