Inhibitor studies on non-photochemical plastoquinone reduction and H(2) photoproduction in Chlamydomonas reinhardtii.
In the absence of PSII, non-photochemical reduction of plastoquinones (PQs) occurs following NADH or NADPH addition in thylakoid membranes of the green alga Chlamydomonas reinhardtii. The nature of the enzyme involved in this reaction has been investigated in vitro by measuring chlorophyll fluorescence increase in anoxia and light-dependent O(2) uptake in the presence of methyl viologen. Based on the insensitivity of these reactions to rotenone, a type-I NADH dehydrogenase (NDH-1) inhibitor, and their sensitivity to flavoenzyme inhibitors and thiol blocking agents, we conclude to the involvement of a type-II NADH dehydrogenase (NDH-2) in PQ reduction. Intact Chlamydomonas cells placed in anoxia have the property to produce H(2) in the light by a Fe-hydrogenase which uses reduced ferredoxin as an electron donor. H(2) production also occurs in the absence of PSII thanks to the existence of a non-photochemical pathway of PQ reduction. From inhibitors effects, we suggest the involvement of a plastidial NDH-2 in PSII-independent H(2) production in Chlamydomonas. These results are discussed in relation to the absence of ndh genes in Chlamydomonas plastid genome and to the existence of 7 ORFs homologous to type-II NDHs in its nuclear genome.
Mus
Florence
F
CEA Cadarache, DSV DEVM Laboratoire d'Ecophysiologie de la Photosynthèse, UMR 6191 CNRS-CEA, Aix-Marseille II, F-13108 Saint-Paul-lez-Durance Cedex, France.
Cournac
Laurent
L
Cardettini
Véronique
V
Caruana
Amandine
A
Peltier
Gilles
G
D000818:Animals; D015687:Cell Hypoxia; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000378:metabolism*; D004579:Electron Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006859:Hydrogen / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010084:Oxidation-Reduction; D010777:Photochemistry; D045332:Photosystem II Protein Complex; D010971:Plastoquinone / Q000378:metabolism*; D011808:Quinone Reductases / Q000037:antagonists & inhibitors; D012402:Rotenone / Q000494:pharmacology; D013379:Substrate Specificity; D020524:Thylakoids / Q000378:metabolism
D004791:Enzyme Inhibitors; D045332:Photosystem II Protein Complex; D012402:Rotenone; D006859:Hydrogen; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases; D009245:NADH Dehydrogenase; D010971:Plastoquinone