Purification of the rice embryo lectin and its binding to nitrogen-fixing bacteria from the rhizosphere of rice

A lectin was purified from rice embryos by aqueous acid extraction of crude embryo powder, followed by ammonium sulfate precipitation, affinity chromatography on agarose p-aminophenyl-β-D-N-acetylglucosamine and gel-filtration on AcA 54. Its homogeneity was checked by polyacrylamide gel electrophoreris, gel-filtration and immunological methods. The hemagglutinating activity of the purified rice lectin was 0.02 μg/ml. This lectin labelled with [ 14 C] acetic anhydride was shown to interact in vitro with different bacteria isolated from the rhizosphere of rice. The most efficient binding was obtained with Beijerinckia V. . The affinity constant K a was (1.04 ± 0.30) × 10 7 M −1 and each bacterium contained 1660 ± 150 lectin receptor sites. In contrast, no interaction between bacteria isolated from the rhizosphere of maize or E. coli K 12 and rice lectin was evidenced.