Endogenous lectins from cultured soybean cells: isolation of a protein immunologically cross-reactive with seed soybean agglutinin and analysis of its role in binding of Rhizobium japonicum

Incubation of Rhizobium japonicum with the cultured soybean cell line SB-1, originally derived from the roots of Glycine max, resulted in specific adhesion of the bacteria to the plant cells. This binding interaction appears to be mediated via carbohydrate recognition, since galactose can inhibit the heterotypic adhesion but glucose cannot. Affinity chromatography, on a Sepharose column derivatized with N-caproyl-galactosamine, of the supernatant fraction of a SB-1 cell suspension after enzymatic removal of cell wall yielded a single polypeptide (Mr approximately 30,000) on immunoblotting analysis with rabbit antibodies directed against seed soybean agglutinin. Fluorescently labeled rabbit anti-seed soybean agglutinin also yielded specific immunofluorescent staining on the cell wall and plasma membrane of the SB-1 cells. These results suggest that one likely candidate that may mediate the recognition between the Rhizobium and the soybean cells is the endogenously produced SB-1 lectin. This notion is supported by the observation that rabbit anti-seed soybean agglutinin blocked the Rhizobium-soybean cell adhesion, whereas control antibodies did not.