The role of extracellular pH-homeostasis in potato resistance to ring rot pathogen

Different cultivars of in vitro plants of potato Solanum tuberosum L. were cultivated with a bacterium Clavibacter michiganensis ssp. sepedonicus (Spi eck. et Kott.) Skaptason et Burkh., causing wilt of the overground part and ring rot of tubers. Development of disease symptoms (chlorosis, growth sup pression) closely correlated with strong acidification of the medium, cause d by the bacterium producing extracellular polysaccharides. However, root c ells of the host plant (potato) and other nonhost plants (seedlings of toma to, wheat and radish) were able to restore extracellular pH. The efficiency of such restoration correlated with the resistance of the potato cultivar to bacteriosis. Plasma membrane and vacuolar H--ATPases were not involved i n the stabilization of extracellular pH-homeostasis, but a significant role was played by the buffer capacity of the cells. The maintenance of pH-home ostasis in the plants is inferred to be one of the main factors of nonspeci fic resistance.