Binding between pole bean (Phaseolus vulgaris L.) lectin and rhizobia that do or do not nodulate the pole bean

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Abstract
The pole bean (Phaseolus vulgaris L. cv. Kentucky Wonder) was nodulated not only by Rhizobium phaseoli 127K14 but also by Rhizobium sp. 127E15, R. leguminosarum 92A3, and R. trifolii 0403. It was not, however, nodulated by R. trifolii ATCC 14481 and R. japonicum 61A118. The binding between pole bean lectin (PBL) and various strains of Rhizobium that can or cannot nodulate the pole bean was tested. Using rabbit antibodies prepared against purified PBL, the lectin was shown by immunofluorescence microscopy to be present on the pole bean root hair surface. The binding between PBL and exponentially growing rhizobia was quantified by a radial immunodiffusion technique. PBL was found to bind to all rhizobia tested whether they nodulate the pole bean or not. The amount of PBL bound to R. phaseoli 127K14, Rhizobium sp. 127E15,R. leguminosarum 92A3, R. trifolii 0403, R. trifolii ATCC 14481, and R. japonicum 61A118 was 3.7, 4.0, 7.4, 5.7, 7.8, and 6.5 μg per 109 cells, respectively. Although hemagglutination activity of PBL was inhibited by N-acetyl-D-galactosamine, the binding betwen PBL and rhizobia was strongly inhibited by D-gluconate, D-galacturonate, and polygalacturonate. The latter three carbohydrates did not inhibit hemagglutination. The results suggest that the sugar specificity of PBL for binding rhizobia may be different than that for the interaction with erythrocytes. Since the sugar specificities of PBL and soybean lectin for binding R. japonicum are different, rhizobia such as R. japonicum 61A118 may have multiple independent binding sites, each having different sugar specificity, for lectins of various legumes.