The Hypersensitive Reaction of Tobacco to Pseudomonas syringae pv. pisi: Activation of a Plasmalemma K

Net electrolyte efflux from suspension-cultured tobacco cells undergoing the hypersensitive reaction to Pseudomonas syringae pv. pisi resulted from a specific efflux of K + which was accompanied by an equimolar net influx of H + . These fluxes began 60 to 90 minutes after inoculation of tobacco cells with bacteria, reached maximum rates of 6 to 9 micromoles per gram fresh weight tobacco cells per hour within 2.5 to 3 hours, and dropped below 4 micromoles per gram per hour within 5 hours. Tobacco cells lost approximately 35% of total K + during this period, and average cellular pH declined by approximately 0.75 pH unit. These events were accompanied by a 30% decrease in cellular ATP. K + and H + fluxes were inhibited by the protonophore ( p -trifluoromethoxy)carbonyl cyanide phenylhydrazone and by increasing the K + concentration of the external solution. Tobacco leaf discs inoculated with the bacterium also exhibited a specific net K + efflux and H + influx. These results suggest that induction of the hypersensitive reaction in tobacco proceeds through the activation of a passive plasmalemma K + /H + exchange mechanism. It is hypothesized that activation of this exchange is a major contributing factor in hypersensitive plant cell death.