title: Photosystem II cycle activity and alternative electron transport in the diatom Phaeodactylum tricornutum under dynamic light conditions and nitrogen limitation.
abstract: Alternative electron sinks are an important regulatory mechanism to dissipate excessively absorbed light energy particularly under fast changing dynamic light conditions. In diatoms, the cyclic electron transport (CET) around Photosystem II (PS II) is an alternative electron transport pathway (AET) that contributes to avoidance of overexcitation under high light illumination. The combination of nitrogen limitation and high-intensity irradiance regularly occurs under natural conditions and is expected to force the imbalance between light absorption and the metabolic use of light energy. The present study demonstrates that under N limitation, the amount of AET and the activity of CETPSII in the diatom Phaeodactylum tricornutum were increased. Thereby, the activity of CETPSII was linearly correlated with the amount of AET rates. It is concluded that CETPSII significantly contributes to AET in P. tricornutum. Surprisingly, CETPSII was found to be activated already at the end of the dark period under N-limited conditions. This coincided with a significantly increased degree of reduction of the plastoquinone (PQ) pool. The analysis of the macromolecular composition of cells of P. tricornutum under N-limited conditions revealed a carbon allocation in favor of carbohydrates during the light period and their degradation during the dark phase. A possible linkage between the activity of CETPSII and degree of reduction of the PQ pool on the one side and the macromolecular changes on the other is discussed.
authors.affiliation: Department of Biology, University of Leipzig, Johannisallee 21-23, 04103, Leipzig, Germany.
authors.forename: Heiko
authors.initials: H
authors.lastname: Wagner
authors.affiliation: Department of Biology, University of Leipzig, Johannisallee 21-23, 04103, Leipzig, Germany. tjakob@rz.uni-leipzig.de.
authors.forename: Torsten
authors.initials: T
authors.lastname: Jakob
authors.affiliation: Institute for Coastal Research and Environment (ILE), UMRi 7266 'LIENSs', CNRS/University of La Rochelle, 2 rue Olympe de Gouges, 17000, La Rochelle Cedex, France.|Department of Biology, UMI 3376 TAKUVIK, CNRS/University Laval, Pavillon Alexandre-Vachon, 1045 avenue de la Médecine, Québec, Québec, G1V 0A6, Canada.
authors.forename: Johann
authors.initials: J
authors.lastname: Lavaud
authors.affiliation: Department of Biology, University of Leipzig, Johannisallee 21-23, 04103, Leipzig, Germany.|German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, 04103, Leipzig, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Wilhelm
mesh_terms: D002244:Carbon / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D003624:Darkness; D017377:Diatoms / Q000502:physiology* / Q000528:radiation effects; D004579:Electron Transport / Q000528:radiation effects; D005453:Fluorescence; D008027:Light; D009584:Nitrogen / Q000172:deficiency*; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism* / Q000528:radiation effects; D010971:Plastoquinone / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002244:Carbon; D009584:Nitrogen; D010971:Plastoquinone; D000077194:Chlorophyll A
keywords: Cyclic electron transport; Diatom; FTIR spectroscopy; Macromolecular composition; Non-photochemical quenching