MECHANISM FOR STABILIZATION OF APOPLASTIC PH DISTURBED BY ACIDIC EXTRACELLULAR POLYSACCHARIDES OF RING-ROT CAUSAL AGENT IN POTATO TISSUE

Early changes in pH caused by acidic extracellular polysaccharides (EP S) of the potato ring-rot causal agent (Clavibacter michiganensis subs p, sepedonicus) and the mechanism for apoplastic pH stabilization were studied in the root cells of test-tube plants of potato (Solanum tube rosum) cultivars differing in their resistance to the pathogen. In the cells of susceptible cultivars, neutralization of EPS caused a rapid short-term alkalinization of the extracellular solution followed by pH fluctuations. Such changes were not observed in the cells of resistan t potato cultivars or non-host (wheat) plants. The vacuolar buffer cap acity, which was higher in the tissues of resistant cultivars as compa red with the susceptible ones, played a considerable role in the resto ration of pH of extracellular solution acidified by EPS, whereas plasm alemma and tonoplast H+-ATPases were not involved in this reaction.