Journal Article

NAD(P)H Dehydrogenase-Dependent, Antimycin A-Sensitive Electron Donation to Plastoquinone in Tobacco Chloroplasts

Tsuyoshi Endo, Toshiharu Shikanai, Fumihiko Sato and Kozi Asada

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 39, issue 11, pages 1226-1231
Published in print November 1998 | ISSN: 0032-0781
Published online November 1998 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/oxfordjournals.pcp.a029324
NAD(P)H Dehydrogenase-Dependent, Antimycin A-Sensitive Electron Donation to Plastoquinone in Tobacco Chloroplasts

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Cyclic electron transport around PSI through the NAD(P)H dehydrogenase complex (NDH) in tobacco leaf disks, measured as an increase in the dark level of Chl fluorescence after the onset of darkness, was inhibited by antimycin A, an inhibitor of ferredoxin quinone reductase (FQR), suggesting that antimycin A inhibits not only the FQR-mediated cyclic flow but also the NDH-dependent flow. This electron flow was inhibited also by amytal, an inhibitor of mitochondrial NDH and by nigericin. The reduction of plastoquinone was detected when NADPH and ferredoxin were added to the suspension of the osmotically ruptured chloroplasts of the wild type and NDH-defective mutant. Because the addition of NADPH alone did not induce the reduction, membrane-bound ferredoxin NADP+reductase (FNR) was supposed to reduce ferredoxin, which may be a more direct electron donor for the plastoquinone reduction. The presence of two types of reducing enzymes was suggested from the bi-phasic inhibition of plastoquinone reduction by antimycin A in the wild type. It is proposed that the reducing activity inhibited by antimycin A at a low concentration is attributed to FQR and the less sensitive activity to NDH.

Keywords: Antimycin A; Chlororespiration; Cyclic electron transport; Ferredoxin quinone reductase (FQR); NAD(P)H dehydrogenase (NDH, EC 1.6.99.3); Tobacco (Nicotiana tabacum)

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Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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