Plant Peptidoglucans Affecting the Phenotypic Expression of Rhizobial Nitrogenase

Abstract

Dialysable substances capable of influencing rhizobial nitrogenase activity in vitro were obtained from Glycine max root cells during transfilter coculture with Rhizobium japonicum. These substances from the liquid plant-conditioned medium were chromatographed on Sephadex G-25, DEAE- cellulose and carboxymethylcellulose and on a concanavalin A-Sepharose column. The separated active column fractions initiated the phenotypic expression of nitrogenase activity (C₂H₂ reduction, H₂ production) in different Rhizobium strains. Hydrolysis of these column fractions showed them to contain a small peptide and a glucan. Analysis of active fractions also showed the presence of bound copper. It was concluded that the plant fractions involved in stimulating rhizobial nitrogenase activity were peptidoglucans; at least one active fraction may also be a copper metallothionein.