Interaction of lectins from soybean and peanut with rhizobia that nodulate soybean, peanut, or both plants

Four of 14 strains of Rhizobium japonicum from soybean nodulated peanut (Arachis hypogaea L. cultivar Jumbo Virginia), and 3 of 8 Rhizobium sp. strains from peanut nodulate soybean (Glycine max (L.) Merr. cultivar Harosoy 63). Cells of three peanut rhizobia bound fluorescent- and radioisotope-labeled soybean lectin. Two of these strains failed to nodulate soybean, and conversely, two peanut strains that nodulated soybean did not bind to soybean lectin. Both culture medium and age had pronounced effects of the number of peanut rhizobia cells that bound fluorescent-labeled soybean lectin. Harosoy 63 soybean root exudates stimulated the growth of peanut rhizobia, but had no consistent influence on the number of cells that bound soybean lectin. Although extracellular soybean lectin receptors were present in culture fluids from each of the peanut rhizobia whose cells bound the lectin, the titer of receptors was greatest for strains 3G4b5. The affinity constants for the adherence of soybean lectin to Rhizobium sp. 3G4b5 cells from cultures of various ages ranged from 4.2 X 10(6) to 4.9 X 10(6) M-1, and the number of lectin binding sites per cell decreased as cells aged. Cells of the soybean and peanut rhizobia did not bind fluorescent- or radioisotope-labeled peanut lectin. The results indicate that there is no relationship between the ability of peanut and soybean rhizobia to nodulate the reciprocal host plant and their ability to bind to the lectin of that plant.