Resistance induction in barley coleoptile cells by intracellular pH decline

Cytoplasmic acidification in suspension-cultured plant cells has been chara cterized as a common intracellular response of some kinds of plant cells to elicitors. Expression of various defense genes in these cells has been inc reased by the cytoplasmic acidification itself without treatment by elicito rs. It is not evident, however, whether or not cells with acidified cytopla sm actually exhibit resistance to the pathogen because of the lack of an ad equate infection system between cultured plant cells and some pathogens. Us ing barley coleoptiles rather than suspension-cultured cells, we demonstrat ed both detection of cellular pH decline and increased resistance to Blumer ia graminis. The cytoplasmic pH of barley coleoptile cells floated on 1 mM citrate buffer (CB), pH 4.0, became 0.5 unit lower than that of cells float ed on 1 mM CB, pH 8.0, within 30 min after treatment. The penetration effic iency of B, graminis into the coleoptile was decreased in a pH-dependent ma nner; that is, when the coleoptiles were floated on 1 mM CB, pH 8.0, the pe netration efficiency of the fungi was about 80%, In contrast, when the cole optiles were floated on acidic buffers, the penetration efficiency decrease d in parallel the decline of pH and the penetration efficiency reached 0% w hen coleoptiles were floated on 1 mM CB, pH 4.0. Morphogenesis of appressor ia on the coleoptiles floating on CB was not influenced. The lowered penetr ation efficiency at lower pH was partially cancelled when the barley coleop tiles were irradiated with UV for 5 min prior to B, graminis inoculation. T hese findings suggest that the decline in cytoplasmic pH in barley coleopti le cells increases resistance to the pathogenic fungus B, graminis.