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An original adaptation of photosynthesis in the marine green alga Ostreococcus
Cardol, P.; Bailleul, B.; Rappaport, F.; Derelle, E.; Beal, D.; Breyton, C.; Bailey, S.; Wollman, F.; Grossman, A.; Moreau, H.; Finazzi, G. (2008). An original adaptation of photosynthesis in the marine green alga Ostreococcus. Proc. Natl. Acad. Sci. U.S.A. 105(22): 7881-7886
In: Proceedings of the National Academy of Sciences of the United States of America. The Academy: Washington, D.C.. ISSN 0027-8424, more
Peer reviewed article  

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Keyword
    Marine
Author keywords
    marine environment; PTOX; water cycle; eletron flow; photoprotection

Authors  Top 
  • Cardol, P., more
  • Bailleul, B.
  • Rappaport, F.
  • Derelle, E.
  • Beal, D.
  • Breyton, C.
  • Bailey, S.
  • Wollman, F.
  • Grossman, A.
  • Moreau, H.
  • Finazzi, G.

Abstract
    Adaptation of photosynthesis in marine environment has been examined in two strains of the green, picoeukaryote Ostreococcus: OTH95, a surface/high-light strain, and RCC809, a deep-sea/low-light strain. Differences between the two strains include changes in the light-harvesting capacity, which is lower in OTH95, and in the photoprotection capacity, which is enhanced in OTH95. Furthermore, RCC809 has a reduced maximum rate of O2 evolution, which is limited by its decreased photosystem I (PSI) level, a possible adaptation to Fe limitation in the open oceans. This decrease is, however, accompanied by a substantial rerouting of the electron flow to establish an H2O-to-H2O cycle, involving PSII and a potential plastid plastoquinol terminal oxidase. This pathway bypasses electron transfer through the cytochrome b6f complex and allows the pumping of “extra” protons into the thylakoid lumen. By promoting the generation of a large ?pH, it facilitates ATP synthesis and nonphotochemical quenching when RCC809 cells are exposed to excess excitation energy. We propose that the diversion of electrons to oxygen downstream of PSII, but before PSI, reflects a common and compulsory strategy in marine phytoplankton to bypass the constraints imposed by light and/or nutrient limitation and allow successful colonization of the open-ocean marine environment.

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