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Plant Cell Physiol. 2016 Jul;57(7):1354-1363. Epub 2016 Mar 7.

The Water to Water Cycles in Microalgae.

Author information

1
Laboratoire de Physiologie Cellulaire et Végétale, UMR 5168, Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'Energie Atomique-Université Grenoble Alpes, UMR 1414 Institut National de la Recherche Agronomique (INRA) Biosciences and Biotechnology Institute of Grenoble (BIG), Commissariat à l'Energie Atomique (CEA) Grenoble, 38054 Grenoble cedex 9, France.
2
Fermentalg SA, F-33500 Libourne, France.
3
Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Università degli Studi di Milano, Via Celoria 26, 20133 Milan, Italy.
4
Laboratoire de Physiologie Cellulaire et Végétale, UMR 5168, Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'Energie Atomique-Université Grenoble Alpes, UMR 1414 Institut National de la Recherche Agronomique (INRA) Biosciences and Biotechnology Institute of Grenoble (BIG), Commissariat à l'Energie Atomique (CEA) Grenoble, 38054 Grenoble cedex 9, France giovanni.finazzi@cea.fr.

Abstract

In oxygenic photosynthesis, light produces ATP plus NADPH via linear electron transfer, i.e. the in-series activity of the two photosystems: PSI and PSII. This process, however, is thought not to be sufficient to provide enough ATP per NADPH for carbon assimilation in the Calvin-Benson-Bassham cycle. Thus, it is assumed that additional ATP can be generated by alternative electron pathways. These circuits produce an electrochemical proton gradient without NADPH synthesis, and, although they often represent a small proportion of the linear electron flow, they could have a huge importance in optimizing CO2 assimilation. In Viridiplantae, there is a consensus that alternative electron flow comprises cyclic electron flow around PSI and the water to water cycles. The latter processes include photosynthetic O2 reduction via the Mehler reaction at PSI, the plastoquinone terminal oxidase downstream of PSII, photorespiration (the oxygenase activity of Rubisco) and the export of reducing equivalents towards the mitochondrial oxidases, through the malate shuttle. In this review, we summarize current knowledge about the role of the water to water cycles in photosynthesis, with a special focus on their occurrence and physiological roles in microalgae.

KEYWORDS:

Electron transport; Microalgae; Photosynthesis; Water to water cycles

PMID:
26955846
DOI:
10.1093/pcp/pcw048
[Indexed for MEDLINE]

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