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Physiology and Biochemistry

Active Oxygen Production During a Bacteria-Induced Hypersensitive Reaction in Tobacco Suspension Cells. L. Dale Keppler, United States Department of Agriculture, ARS, Microbiology and Plant Pathology Laboratory, Beltsville, MD 20705; C. Jacyn Baker, and Merelee M. Atkinson. United States Department of Agriculture, ARS, Microbiology and Plant Pathology Laboratory, Beltsville, MD 20705. Phytopathology 79:974-978. Accepted for publication 10 May 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989. DOI: 10.1094/Phyto-79-974.

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, and 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).