Transgenic tobacco plants overexpressing chloroplastic ferredoxin-NADP(H) reductase display normal rates of photosynthesis and increased tolerance to oxidative stress.
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.
Rodriguez
Ramiro E
RE
Instituto de Biología Molecular y Celular de Rosario, División Biología Molecular, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, S2002LRK Rosario, Argentina.
Lodeyro
Anabella
A
Poli
Hugo O
HO
Zurbriggen
Matias
M
Peisker
Martin
M
Palatnik
Javier F
JF
Tognetti
Vanesa B
VB
Tschiersch
Henning
H
Hajirezaei
Mohammad-Reza
MR
Valle
Estela M
EM
Carrillo
Néstor
N
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*
D006540:Herbicides; D002245:Carbon Dioxide; D005287:Ferredoxin-NADP Reductase; D010269:Paraquat