Properties of extracellular polysaccharides of potato ring rot pathogen and corresponding recognition sites of potato cell walls

The properties of extracellular polysaccharides of the potato ring rot path ogen Clavibacter michiganensis subsp. sepedonicus (Cms) and the correspondi ng recognition sites isolated from cell walls of potato suspension cultures have been studied. Extracellular polysaccharides of Cms consist of 4-6 com ponents, which differ greatly in molecular mass (from <1 kD to >700 kD), an d are capable of formation of associates stabilized by electrostatic intera ctions in the presence of calcium. Using affinity column chromatography, si tes possessing affinity for the total extracellular polysaccharide complex of Cms were isolated from cell walls of suspension cultures of three potato varieties with different resistance to the pathogen. The content of the re ceptor sites consisting of glycopeptides and sugars for the variety devoid of resistance was 10 times greater than that for the resistant variety. In the receptor fraction for the latter variety, only sugars were found. The m olecular masses of the components of the receptor fraction of cell walls we re from 39 to 86 kD. Polypeptides in the recognition sites for the resistan t variety escaped detection in electrophoretic patterns. Study of the amino acid composition of the receptor sites of cell walls showed that the sites of the resistant variety contained trace amounts of only seven amino acids . In the sites of the receptive variety 14 amino acids were found, the cont ent of polar amino acids being twice as large as that of nonpolar amino aci ds. Among polar amino acids, glutamine and glycine prevailed, whereas among nonpolar amino acids valine was dominant. We suggest that one of the reaso ns of variety-specific resistance of potato to Cms is the absence or a low content of the sites revealing the affinity for bacterial extracellular pol ysaccharides on the plant cell surface.