Enhanced Resistance to Viruses in 'Columbia' Is Dependent on Salicylic Acid, Correlates with High Glutathione Levels, and Extends to Plant-Pathogenic Bacteria and Abiotic Stress.

Our earlier research showed that an interspecific tobacco hybrid ( 'Columbia' [NEC]) displays elevated levels of salicylic acid (SA) and enhanced resistance to localized necrotic symptoms (hypersensitive response [HR]) caused by tobacco mosaic virus (TMV) and tobacco necrosis virus (TNV), as compared with another interspecific hybrid ( [NE]) derived from the same parents. In the present study, we investigated whether symptomatic resistance in NEC is indeed associated with the inhibition of TMV and TNV and whether SA plays a role in this process. We demonstrated that enhanced viral resistance in NEC is manifested as both milder local necrotic (HR) symptoms and reduced levels of TMV and TNV.

Reactive Oxygen Species Contribute to Symptomless, Extreme Resistance to in Tobacco.

Here we show that in tobacco ( cultivar Samsun NN ) the development of gene-mediated, symptomless, extreme resistance to (PVX) is preceded by an early, intensive accumulation of the reactive oxygen species (ROS) superoxide (O·), evident between 1 and 6 h after inoculation and associated with increased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activities. This suggests a direct contribution of this ROS to virus restriction during symptomless, extreme resistance. Superoxide inhibition in PVX-inoculated leaves by infiltration of antioxidants (superoxide dismutase [SOD] and catalase [CAT]) partially suppresses extreme resistance in parallel with the appearance of localized leaf necrosis resembling a hypersensitive resistance (HR) response.

Superoxide (O) accumulation contributes to symptomless (type I) nonhost resistance of plants to biotrophic pathogens.

Nonhost resistance is the most common form of disease resistance exhibited by plants against most pathogenic microorganisms. Type I nonhost resistance is symptomless (i.e.

Up-regulation of antioxidants in tobacco by low concentrations of H₂O₂ suppresses necrotic disease symptoms.

Pretreatment of tobacco leaves with low concentrations (5 to 10 mM) of H₂O₂ suppressed hypersensitive-type necrosis associated with resistance to Tobacco mosaic virus (TMV) or Pseudomonas syringae pv. phaseolicola. The same pretreatment resulted in suppression of normosensitive necrosis associated with susceptibility to Botrytis cinerea.