RESUMO
The root exudate of Arachis hypogea (groundnut) and its seed lectin peanut agglutinin were found to stimulate the synthesis of exopolysaccharide and capsular polysaccharide of the microsymbiont cowpea Rhizobium strain JLn (c). The synthesis of capsular polysaccharide was enhanced 1·5-fold and 2-fold in the presence of peanut agglutinin and root exudate, respectively. The synthesis of capsular polysaccharide was suppressed in the presence of different forms of combined nitrogen. Quantitative differences were also detected between the exopolysaccharide of cells grown in the presence and absence of root exudate. Electron microscopic examination of negatively stained lectin-treated JLn (c) cells showed an increased deposition of capsular polysaccharide surrounding the cells. Hurthermore, ex planta nitrogenase activity of JLn(c) cells in the presence of lectin was found to be enhanced by 63% in correlation with the increased synthesis of polysaccharides.