Azospirillum brasilense colonisation of wheat roots and the role of lectin-carbohydrate interactions in bacterial adsorption and root-hair deformation

The dynamics of adsorption of the nitrogen-fixing soil bacteria Azospirillu m brasilense 75 and 80 (isolated from soil samples collected in Saratov Obl ast, southern Russia) and A. brasilense Sp245 to the roots of seedlings of common spring wheat was studied in relation to inoculum size, period of inc ubation with the roots and bacterial-growth phase. The number of root-attac hed cells increased with increasing size of inoculum and time of contact. T he saturation of root-surface adsorption was observed by 24 h of co-incubat ion for A. brasilense 75, by 6 h for A. brasilense 80, and by 3 h for A. br asilense Sp245. The firmness of bacterial-root attachment increased after e xtended co-incubation. Differences in the adsorption kinetics of the azospi rilla were found that were associated with bacterial-growth phases. Azospir illa attached to the roots of their host cultivar more actively than they d id to the roots of a non-host cultivar. Adsorption was partially inhibited when the roots were treated with N-acetyl-D-glucosamine. Maximal inhibition occurred after a 3-h exposure of the roots to the bacteria. Root-hair defo rmation induced with polysaccharide-containing complexes from the Azospiril lum capsular material was inhibited by N-acetyl-D-glucosamine and chitotrio se, specific haptens of wheat germ agglutinin. A possible mechanism of the mutual influence of bacteria and plants may involve key roles of wheat germ agglutinin, present on the roots, and the polysaccharide-containing compon ents of the Azospirillum capsule.