A loss of resistance to avirulent bacterial pathogens in tobacco is associated with the attenuation of a salicylic acid-potentiated oxidative burst.
The role of salicylic acid (SA) in events occurring before cell death during the hypersensitive reaction (HR) was investigated in leaves of wild-type tobacco Samsun NN and in transgenic lines expressing salicylate hydroxylase (35S-SH-L). Challenge of 35S-SH-L tobacco with avirulent strains of Pseudomonas syringae gave rise to symptoms resembling those normally associated with a compatible response to virulent strains in terms of visible phenotype, kinetics of bacterial multiplication, and escape from the infection site. Compared with responses in wild-type tobacco, both the onset of plant cell death and the induction of an active oxygen species-responsive promoter (AoPR1-GUS) were delayed following challenge of 35S-SH-L plants with avirulent bacteria. The oxidative burst occurring after challenge with avirulent bacteria was visualized histochemically and quantified in situ. H2O2 accumulation at reaction sites was evident within 1 h after inoculation in wild-type tobacco, whereas in 35S-SH-L plants the onset of H2O2 accumulation was delayed by 2-3 h. The delay in H2O2 generation was correlated with a reduction in the transient rise in SA that usually occurred within 1-2 h following inoculation in wild-type plants. Our data indicate that an early transient rise in SA potentiates the oxidative burst, with resultant effects on accumulation of H2O2, plant cell death and also defence-gene induction, factors that together may determine the outcome of plant-pathogen interactions.
Mur
L A
LA
Institute of Biological Sciences, University of Wales, Aberystwyth, Edward Llwyd Building, Penglais Campus, Aberystwyth, Ceredigion SY23 3DA, UK.
Brown
I R
IR
Darby
R M
RM
Bestwick
C S
CS
Bi
Y M
YM
Mansfield
J W
JW
Draper
J
J
D006861:Hydrogen Peroxide / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000382:microbiology; D010947:Plants, Toxic; D011401:Promoter Regions, Genetic; D011549:Pseudomonas / Q000472:pathogenicity*; D016897:Respiratory Burst; D020156:Salicylic Acid / Q000378:metabolism*; D014026:Nicotiana / Q000235:genetics / Q000382:microbiology*; D014774:Virulence
D006861:Hydrogen Peroxide; D020156:Salicylic Acid