5.4.4
EFFECT OF AN ELEVATED ENDOGENOUS LEVEL OF H2O2 ON THE RESISTANCE OF POTATO TO PHYTOPHTHORA INFESTANS

M SCHNEIDER and J-P METRAUX

Department of Biology, Plant Biology, University of Fribourg, CH-1700 Fribourg, Switzerland

Background and objectives
Several observations indicate that active oxygen species might play an important role in plant defence against pathogens. Transgenic potato plants expressing a fungal gene that encodes glucose oxidase, which generates H2O2, exhibited strong resistance to the bacterial soft rot disease caused by Erwinia carotovora and to late blight caused by Phytophthora infestans [1]. In order to test this further, we have transformed potato plants with a gene encoding a plant oxalate oxidase.This enzyme oxidizes oxalate, which is a degradation product of ascorbate, into CO2and H2O2.

Materials and methods
A wheat oxalate oxidase gene [2] was put under the control of the 35S promoter from CaMV (a constitutive promoter) and inserted into a binary vector (pBin19). Potato (cv. Bintje) internodes were transformed with Agrobacterium tumefaciens strain LBA4404 containing the binary vector. The resistance test was carried out by infecting 10 plants of each transgenic line on three leaves with four drops of 5 Ál containing 150 zoospores of P. infestans strain 94-28.

Results and conclusions
At least five out of eight transgenic lines tested so far presented an increased resistance to P. infestans. This was shown by a reduced number of necroses per plant and by a decreased number of sporangias formed per necrosis. Moreover, the growth of the hyphae in those transgenic plants was markedly reduced. The transgenic lines will now be tested under agronomic conditions in an outdoor field test.

References
1. Wu G, Shortt BJ, Lawrence EB et al., 1995. Plant Cell 7, 1357-1368.
2. Lane BG, Dunwell JM, Ray JA et al., 1993. Journal of Biological Chemistry 268, 12239-12242.