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 pathogen Clavibacter michiganensis subsp. sepedonicus (Cms) and the corresponding recognition sites isolated from cell walls of potato suspension cultures have been studied. Extracellular polysaccharides of Cms consist of 4-6 components, which differ greatly in molecular mass (from <1 kD to >700 kD), and are capable of formation of associates stabilized by electrostatic interactions in the presence of calcium. Using affinity column chromatography, sites 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 receptor 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 molecular masses of the components of the receptor fraction of cell walls were from 39 to 86 kD. Polypeptides in the recognition sites for the resistant 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 content of polar amino acids being twice as large as that of nonpolar amino acids. Among polar amino acids, glutamine and glycine prevailed, whereas among nonpolar amino acids valine was dominant. We suggest that one of the reasons of variety-specific resistance of potato to Cms is the absence or a low content of the sites revealing the affinity for bacterial extracellular polysaccharides on the plant cell surface.