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BIOENERGETICS AND PHOTOSYNTHESIS

Transgenic Tobacco Plants Overexpressing Chloroplastic Ferredoxin-NADP(H) Reductase Display Normal Rates of Photosynthesis and Increased Tolerance to Oxidative Stress¹

Instituto de Biología Molecular y Celular de Rosario, División Biología Molecular, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, S2002LRK Rosario, Argentina (R.E.R., A.L., H.O.P., M.Z., J.F.P., V.B.T., E.M.V., N.C.); and Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung, 06466 Gatersleben, Germany (M.P., H.T., M.-R.H.)

Ferredoxin-NADP(H) reductase (FNR) catalyzes the last step of photosynthetic electron transport in chloroplasts, driving electrons from reduced ferredoxin to NADP⁺. This reaction is rate limiting for photosynthesis under a wide range of illumination conditions, as revealed by analysis of plants transformed with an antisense version of the FNR gene. To investigate whether accumulation of this flavoprotein over wild-type levels could improve photosynthetic efficiency and growth, we generated transgenic tobacco (Nicotiana tabacum) plants expressing a pea (Pisum sativum) FNR targeted to chloroplasts. The alien product distributed between the thylakoid membranes and the chloroplast stroma. Transformants grown at 150 or 700 µmol quanta m^–2 s^–1 displayed wild-type phenotypes regardless of FNR content. Thylakoids isolated from plants with a 5-fold FNR increase over the wild type displayed only moderate stimulation (approximately 20%) in the rates of electron transport from water to NADP⁺. In contrast, when donors of photosystem I were used to drive NADP⁺ photoreduction, the activity was 3- to 4-fold higher than the wild-type controls. Plants expressing various levels of FNR (from 1- to 3.6-fold over the wild type) failed to show significant differences in CO₂ assimilation rates when assayed over a range of light intensities and CO₂ concentrations. Transgenic lines exhibited enhanced tolerance to photooxidative damage and redox-cycling herbicides that propagate reactive oxygen species. The results suggest that photosynthetic electron transport has several rate-limiting steps, with FNR catalyzing just one of them.

² Present address: Department of Plant Physiology and Biochemistry/W5, University of Bielefeld, 33501 Bielefeld, Germany.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Néstor Carrillo (carrillo{at}ibr.gov.ar).

www.plantphysiol.org/cgi/doi/10.1104/pp.106.090449

^* Corresponding author; e-mail carrillo{at}ibr.gov.ar; fax 54–341–4390465.

Received September 28, 2006; accepted December 13, 2006; published December 22, 2006.

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