A loss of resistance to avirulent bacterial pathogens in tobacco is associated with the attenuation of a salicylic acid-potentiated oxidative burst

L A J Mur, I R Brown, R M Darby, Charles Bestwick, Y M Bi, J W Mansfield, J Draper

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Abstract

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.

Original languageEnglish
Pages (from-to)609-621
Number of pages13
JournalThe Plant Journal
Volume23
Issue number5
DOIs
Publication statusPublished - Sep 2000

Keywords

  • salicylic acid
  • potentiation
  • oxidative burst
  • systemic acquired-resistance
  • plant-disease resistance
  • hypersensitive cell-death
  • syringae PV phaseolicola
  • hydrogen-peroxide
  • transgenic tobacco
  • plasma-membrane
  • active oxygen
  • signal-transduction
  • NADPH oxidase

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