title: Alternative photosynthetic electron flow to oxygen in marine Synechococcus.
abstract: Cyanobacteria dominate the world's oceans where iron is often barely detectable. One manifestation of low iron adaptation in the oligotrophic marine environment is a decrease in levels of iron-rich photosynthetic components, including the reaction center of photosystem I and the cytochrome b6f complex [R.F. Strzepek and P.J. Harrison, Photosynthetic architecture differs in coastal and oceanic diatoms, Nature 431 (2004) 689-692.]. These thylakoid membrane components have well characterised roles in linear and cyclic photosynthetic electron transport and their low abundance creates potential impediments to photosynthetic function. Here we show that the marine cyanobacterium Synechococcus WH8102 exhibits significant alternative electron flow to O2, a potential adaptation to the low iron environment in oligotrophic oceans. This alternative electron flow appears to extract electrons from the intersystem electron transport chain, prior to photosystem I. Inhibitor studies demonstrate that a propyl gallate-sensitive oxidase mediates this flow of electrons to oxygen, which in turn alleviates excessive photosystem II excitation pressure that can often occur even at relatively low irradiance. These findings are also discussed in the context of satisfying the energetic requirements of the cell when photosystem I abundance is low.
authors.affiliation: The Carnegie Institution, Department of Plant Biology, 260 Panama Street, Stanford, CA 94305, USA. shaunb@stanford.edu
authors.forename: Shaun
authors.initials: S
authors.lastname: Bailey
authors.forename: Anastasios
authors.initials: A
authors.lastname: Melis
authors.forename: Katherine R M
authors.initials: KR
authors.lastname: Mackey
authors.forename: Pierre
authors.initials: P
authors.lastname: Cardol
authors.forename: Giovanni
authors.initials: G
authors.lastname: Finazzi
authors.forename: Gert
authors.initials: G
authors.lastname: van Dijken
authors.forename: Gry Mine
authors.initials: GM
authors.lastname: Berg
authors.forename: Kevin
authors.initials: K
authors.lastname: Arrigo
authors.forename: Jeff
authors.initials: J
authors.lastname: Shrager
authors.forename: Arthur
authors.initials: A
authors.lastname: Grossman
mesh_terms: D000222:Adaptation, Physiological; D002734:Chlorophyll / Q000378:metabolism; D004579:Electron Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007501:Iron / Q000378:metabolism*; D000090463:Iron Deficiencies; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D011435:Propyl Gallate / Q000494:pharmacology; D012623:Seawater / Q000737:chemistry; D046940:Synechococcus / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D020524:Thylakoids / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C001785:chlorophyll P 700; D011435:Propyl Gallate; D007501:Iron; D010088:Oxidoreductases; D010100:Oxygen