Alteration of Plasmalemma Sucrose Transport inPhaseolus vulgarisbyPseudomonas syringaepv.syringaeand its Association with K+/ H+Exchange

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Abstract
Plasmalemma H+ gradients created by H+-extruding ATPases are believed to drive the active transport of sucrose, amino acids, and inorganic ions into plant cells. Pseudomonas syringae pv. syringae, a bean pathogen, activates a host plasma membrane K+ efflux/H+ influx exchange, which increases apoplastic pH from approximately 5.5 to 7.5 with consequent reduction or reversal of the H+ gradient. Because the exchange response is strongly associated with bacterial multiplications in bean leaves, we have investigated the hypothesis that it promotes bacterial multiplication by altering host plasmalemma nutrient transport and thereby increasing availability of nutrients to bacteria. P. s. pv. syringae induced increased efflux and decreased influx of sucrose in bean tissue within 2-4 hr after inoculation. A bacterial mutant unable to induce the exchange response or multiply in bean leaves had no effect on sucrose transport. Uninoculated leaf tissue was infiltrated with buffers at pH 7-8 or with 25-50 mM K+ salts to approximate intercellular conditions resulting from the exchange. These treatments induced changes in sucrose transport comparable to those induced by wild-type bacteria. Our findings indicate that the strong association of K+/H+ exchange with bacterial multiplication in bean leaves could be partly due to increased availability of sucrose in host intercellular spaces.