Transgenic tobacco plants overexpressing chloroplastic ferredoxin-NADP(H) reductase display normal rates of photosynthesis and increased tolerance to oxidative stress

RODRIGUEZ, R E; LODEYRO, A.; POLI, H O; ZURBRIGGEN, M.; PALATNIK, JAVIER FERNANDO; TOGNETTI, V B; TSCHIERSCH, H; HAJIREZAEI, M; VALLE, E M; CARRILLO, N

PLANT PHYSIOLOGY.

Año: 2006 p. 1 - 1

0032-0889

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 the analysis of plants transformed with an antisense version of the FNR gene. To investigate if accumulation of this flavoprotein over the wild-type levels could improve photosynthetic efficiency and growth, we generated transgenic tobacco plants expressing a pea FNR targeted to chloroplasts. The alien product distributed between the thylakoid membranes and the chloroplast stroma. Transformants grown at 150 or 700 m mol quanta m-2 s-1 displayed wild-type phenotypes, irrespective of FNR contents. Thylakoids isolated from plants with a 5-fold FNR increase over the wild type displayed only a moderate stimulation (~ 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 activities were 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 wide range of light intensities and CO2 concentrations. The 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.