Increased Sensitivity of Photosynthesis to Antimycin A Induced by Inactivation of the Chloroplast ndhB Gene. Evidence for a Participation of the NADH-Dehydrogenase Complex to Cyclic Electron Flow around Photosystem I

• Published in: Plant physiology (Bethesda) 2001-04, Vol.125 (4), p.1919-1929
• Main Authors: Joët, Thierry, Cournac, Laurent, Eva M. Horvath, Medgyesy, Peter, Peltier, Gilles
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Antimycin A - pharmacology; Bioenergetics and Photosynthesis; Biological and medical sciences; C3 plants; Carbon Dioxide - metabolism; Chlorophyll - metabolism; Chlorophylls; Chloroplasts; Economic plant physiology; Electron Transport; Fluorescence; Fundamental and applied biological sciences. Psychology; Kinetics; Leaves; Light; Light-Harvesting Protein Complexes; Metabolism; Methacrylates; NADH Dehydrogenase - metabolism; Net assimilation, photosynthesis, carbon metabolism. Photorespiration, respiration, fermentation (anoxia, hypoxia); Nicotiana - drug effects; Nicotiana - genetics; Nicotiana - physiology; Nutrition. Photosynthesis. Respiration. Metabolism; Photorespiration; Photosynthesis; Photosynthesis - drug effects; Photosynthesis - physiology; Photosynthesis, respiration. Anabolism, catabolism; Photosynthetic Reaction Center Complex Proteins - metabolism; Photosystem I Protein Complex; Plant physiology and development; Plant Proteins - genetics; Plants; Plants, Toxic; Plastids - genetics; Respiration; Thiazoles - pharmacology; Thylakoids
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.125.4.1919

Tobacco (Nicotiana tabacum var Petit Havana) ndhB-inactivated mutants ($ndhB^{-}$) obtained by plastid transformation (E. M. Horvath, S. O. Peter, T. Joët, D. Rumeau, L. Cournac, G. V. Horvath, T. A. Kavanagh, C. Schäfer, 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 CO2 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 $ndhB^{-}$ and wild type (WT). When leaf discs were treated with 5 μM 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% O2, 2,500 μL L-1 CO2), 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 CO2 assimilation in $ndhB^{-}$. The effect of antimycin A on $ndhB^{-}$ could not be mimicked by myxothiazol, an inhibitor of the mitochondrial cytochrome bc1 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.