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-beta-D-N-acetylglucosamine and gel-filtration on AcA 54. Its homogeneity was checked by polyacrylamide gel electrophoresis, gel-filtration and immunological methods. The hemagglutinating activity of the purified rice lectin was 0.02 micrograms/ml. This lectin labelled with [14C] 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 Ka was (1.04 +/- 0.30) X 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.