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Cyclic electron flow under saturating excitation of dark-adapted Arabidopsis leaves

2004; Elsevier BV; Volume: 1656; Issue: 2-3 Linguagem: Inglês

10.1016/j.bbabio.2004.03.010

1879-2650

Pierre Joliot, Daniel J. Beal, Anne Joliot,

Light effects on plants

The rate of cyclic electron flow measured in dark-adapted leaves under aerobic conditions submitted to a saturating illumination has been performed by the analysis of the transmembrane potential changes induced by a light to dark transfer. Using a new highly sensitive spectrophotometric technique, a rate of the cyclic flow of ∼130 s−1 has been measured in the presence or absence of 3-(3,4-dichloro-phenyl)-1,1-dimethylurea (DCMU). This value is ∼1.5 times larger than that previously reported [Proc. Natl. Acad. Sci. U. S. A. 99 (2001) 10209]. We have characterized in the presence or absence of DCMU charge recombination process (t1/2∼60 μs) that involves P700+ and very likely the reduced form of the iron sulfur acceptor FX. This led to conclude that, under saturating illumination, the PSI centers involved in the cyclic pathway have most of the iron sulfur acceptors FA and FB reduced. In the proposed mechanism, electrons are transferred from a ferredoxin bound to a site localized on the stromal side of the cytochrome b6f complex to the Qi site. Two possible models of the organization of the membrane complexes are discussed, in which the cyclic and linear electron transfer chains are isolated one from the other.