Association of Host Plasma Membrane K+/H+Exchange with Multiplication ofPseudomonas syringaepv.syringaeinPhaseolus vulgaris

Abstract

Pseudomonas syringae pv. syringae, a bean pathogen, induced plasma membrane K+ efflux/net H+ influx exchange and multiplied rapidly in bean leaf tissue. Nine bacterial mutants previously selected for impaired ability to induce a hypersensitive response and the K+/H+ response in tobacco were also examined. Mutants unable to induce K+/H+ exchange in bean did not multiply within this host, whereas weak, moderate, and strong inductions were associated with slow, moderate, and rapid population growth, respectively. Time course experiments indicated that induction of K+/H+ exchange preceded the onset of bacterial population growth. Continued operation of the exchange increased host intercellular fluid pH from approximately 5.5 to 7.5. Infiltration of host intercellular spaces with pH 7.0-8.0 buffers promoted growth of a nonpathogenic bacterial mutant, whereas pH 6.0 buffer inhibited growth of the wild-type strain. These results suggest that increased pH of host intercellular fluids resulting from K+/H+ exchange promotes bacterial multiplication. In view of the role of H+ gradients in active transport of sucrose, amino acids, and inorganic ions across the plasmalemma, we hypothesize that increased intercellular pH leads to increased nutrient levels in intercellular spaces where bacteria reside.