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Curr Opin Plant Biol. 2015 Jun;25:71-8. doi: 10.1016/j.pbi.2015.04.009. Epub 2015 May 20.

Sharing light between two photosystems: mechanism of state transitions.

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Department of Botany and Plant Biology, University of Geneva, 30 quai Ernest Ansermet, 1211 Geneva 4, Switzerland. Electronic address:
Dipartimento di Biotecnologie, Università degli Studi di Verona, 15, strada Le Grazie, 37134 Verona, Italy.


In the thylakoid membrane, the two photosystems act in series to promote linear electron flow, with the concomitant production of ATP and reducing equivalents such as NADPH. Photosystem I, which is preferentially activated in far-red light, also energizes cyclic electron flow which generates only ATP. Thus, changes in light quality and cellular metabolic demand require a rapid regulation of the activity of the two photosystems. At low light intensities, this is mediated by state transitions. They allow the dynamic allocation of light harvesting antennae to the two photosystems, regulated through protein phosphorylation by a kinase and phosphatase pair that respond to the redox state of the electron transfer chain. Phosphorylation of the antennae leads to remodeling of the photosynthetic complexes.

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