title: Transgenic tobacco plants overexpressing chloroplastic ferredoxin-NADP(H) reductase display normal rates of photosynthesis and increased tolerance to oxidative stress.
abstract: 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 micromol 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.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario, División Biología Molecular, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, S2002LRK Rosario, Argentina.
authors.forename: Ramiro E
authors.initials: RE
authors.lastname: Rodriguez
authors.forename: Anabella
authors.initials: A
authors.lastname: Lodeyro
authors.forename: Hugo O
authors.initials: HO
authors.lastname: Poli
authors.forename: Matias
authors.initials: M
authors.lastname: Zurbriggen
authors.forename: Martin
authors.initials: M
authors.lastname: Peisker
authors.forename: Javier F
authors.initials: JF
authors.lastname: Palatnik
authors.forename: Vanesa B
authors.initials: VB
authors.lastname: Tognetti
authors.forename: Henning
authors.initials: H
authors.lastname: Tschiersch
authors.forename: Mohammad-Reza
authors.initials: MR
authors.lastname: Hajirezaei
authors.forename: Estela M
authors.initials: EM
authors.lastname: Valle
authors.forename: Néstor
authors.initials: N
authors.lastname: Carrillo
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology*; D005287:Ferredoxin-NADP Reductase / Q000235:genetics* / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006540:Herbicides / Q000494:pharmacology; D008027:Light; D018384:Oxidative Stress; D010269:Paraquat / Q000494:pharmacology; D018532:Pisum sativum / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D030821:Plants, Genetically Modified; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*
chemical_list: D006540:Herbicides; D002245:Carbon Dioxide; D005287:Ferredoxin-NADP Reductase; D010269:Paraquat