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IMPLICATIONS D'UN COMPLEXE NAD(P)H DESHYDROGENASE ET D'UNE OXYDASE TERMINALE CHLOROPLASTIQUES DANS LA PHOTOSYNTHESE ET LA CHLORORESPIRATION

Thierry Joet 1
1 LEMP - Laboratoire d'Ecophysiologie Moléculaire des Plantes
BIAM - Institut de Biosciences et Biotechnologies d'Aix-Marseille (ex-IBEB) : DRF/BIAM
Abstract : Thylakoid membranes of higher plants contain respiratory-type proteins of unknown function, namely a NADH dehydrogenase complex (Ndh) and an oxidase (PTOX), respectively homologuous to mitochondrial complex I and alternative oxidase. In order to elucidate the function of the Ndh complex, the ndhB gene has been inactivated by plastid transformation. Chlorophyll fluorescence measurements, performed on transplastomic tobacco plants, showed that the Ndh complex is involved in the non-photochemical reduction of the PQ pool. In mutants deficient in the Ndh complex, both a growth retardation and a decrease in photosynthetic capacities has been measured in conditions where photorespiration is highly active, due to a decreased CO2 avaibility (such as limited water deficit). Based on the effects of antimycin A, an inhibitor of cyclic electron transport, on photosynthesis and on measurments of PS I energy storage by photoacoustic spectroscopy, we conclude to the existence of two pathways of cyclic electron flow around PS I, one of which involving the Ndh complex. This mechanism, regulated by the redox state of electron transport chain putatively through the plastoquinol oxidase activity of PTOX, could re-equilibrate the NADPH/ATP ratio when ATP demand is high, for instance during water deficit.
In order to determine the role of PTOX during photosynthesis, tobacco plants overexpressing this protein have been generated. Based on chlorophyll fluorescence measurements, we show the involvement of PTOX in the non-photochemical oxidation of plastoquinones. We conclude that the Ndh complex and PTOX, both located in stroma lamellae, are components of a chlororespiratory electron transport chain. We propose that chlororespiration, through a fine tuning of the redox state of some inter-system electron carriers, participates to the regulation of cyclic electron transport around PS I.
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https://tel.archives-ouvertes.fr/tel-00009113
Contributor : Thierry Joët <>
Submitted on : Wednesday, April 27, 2005 - 12:37:28 PM
Last modification on : Thursday, March 14, 2019 - 1:23:50 AM
Long-term archiving on: : Friday, April 2, 2010 - 9:36:46 PM

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  • HAL Id : tel-00009113, version 1

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Thierry Joet. IMPLICATIONS D'UN COMPLEXE NAD(P)H DESHYDROGENASE ET D'UNE OXYDASE TERMINALE CHLOROPLASTIQUES DANS LA PHOTOSYNTHESE ET LA CHLORORESPIRATION. Physiologie [q-bio.TO]. Université Montpellier II - Sciences et Techniques du Languedoc, 2001. Français. ⟨tel-00009113⟩

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