Active Oxygen Production During a Bacteria-Induced Hypersensitive Reaction in Tobacco Suspension Cells

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Abstract
In tobacco cell suspensions, onset of the hypersensitive reaction induced by phytopathogenic bacteria can be monitored as increased extracellular pH. Previous reports suggested that active oxygen-initiated lipid peroxidation preceded this increased extracellular pH. Here, we investigated the timing of active oxygen production and increased extracellular pH during the onset of the hypersensitive reaction. Active oxygen levels were monitored by measuring light production (chemiluminescence), in the presence of luminol. Increase in active oxygen levels over time correlated with increased extracellular pH. Pseudomonas syringae pv. syringae (wild-type, a pathogen of wheat) was used to induce a hypersensitive reaction in tobacco cell suspensions. P. s. syringae B7, a Tn5 insertion mutant that does not induce a hypersensitive reaction, P. s. tabaci, a pathogen of tobacco, were used as controls. All bacterial treatments induced transient increases in both active oxygen and extracellular pH between 0 and 1 hr. Concomitant increases of extracellular pH and active oxygen levels were observed between 2 and 4 hr only in tobacco cell suspensions undergoing the hypersensitive reaction (inoculated with wild-type bacteria).