Lectins: a possible basis for specificity in the Rhizobium--legume root nodule symbiosis.

Soybean lectin labeled with fluorescein isothiocyanate combined specifically with all but 3 of 25 strains of the soybean-nodulating bacterium Rhizobium japonicum. The lectin did not bind to any of 23 other strains representative of rhizobia that do not nodulate soybeans. The evidence suggests that an interaction between legume lectins and Rhizobium cells may account for the specificity expressed between rhizobia and host plant in the initiation of the nitrogen-fixing symbiosis.