期刊
PLANT PHYSIOLOGY
卷 125, 期 4, 页码 1919-1929出版社
AMER SOC PLANT BIOLOGISTS
DOI: 10.1104/pp.125.4.1919
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Tobacco (Nicotiana tabacum var Petit Havana) ndhB-inactivated mutants (ndhB(-)) obtained by plastid transformation (E.M. Horvath, S.O. Peter, T. Joet, D. Rumeau, L. Cournac, G.V. Horvath, T.A. Kavanagh, C. Schafer, G. Peltier, P. Medgyesy-Horvath [2000] Plant Physiol 123: 1337-1350) were used to study the role of the NADH-dehydrogenase complex (NDH) during photosynthesis and particularly the involvement of this complex in cyclic electron flow around photosystem I (PSI). Photosynthetic activity was determined on Leaf discs by measuring CO, exchange and chlorophyll fluorescence quenchings during a dark-to-light transition. In the absence of treatment, both non-photochemical and photochemical fluorescence quenchings were similar in ndh(-) and wild type (WT). When leaf discs were treated with 5 muM antimycin A, an inhibitor of cyclic electron flow around PSI, both quenchings were strongly affected. At steady state, maximum photosynthetic electron transport activity was inhibited by 20% in WT and by 50% in ndhB(-). Under non-photorespiratory conditions (2% O(2), 2,500 muL L(-1) CO(2)), antimycin A had no effect on photosynthetic activity of WT, whereas a 30% inhibition was observed both on quantum yield of photosynthesis assayed by chlorophyll fluorescence and on CO(2) assimilation in ndhB(-). The effect of antimycin A on ndhB- could not be mimicked by myxothiazol, an inhibitor of the mitochondrial cytochrome he, complex, therefore showing that it is not related to an inhibition of the mitochondrial electron transport chain but rather to an inhibition of cyclic electron flow around PSI. We conclude to the existence of two different pathways of cyclic electron flow operating around PSI in higher plant chloroplasts. One of these pathways, sensitive to antimycin A, probably involves ferredoxin plastoquinone reductase, whereas the other involves the NDH complex. The absence of visible phenotype in ndhB(-) plants under normal conditions is explained by the complement of these two pathways in the supply of extra-ATP for photosynthesis.
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