INHIBITION OF 1,3-BETA-GLUCAN SYNTHASE FROM GLYCINE-MAX AND PISUM-SATIVUM BY EXOPOLYSACCHARIDES OF BRADYRHIZOBIUM-JAPONICUM AND RHIZOBIUM-LEGUMINOSARUM

The 1,3-β-glucan synthase activity of Pisum sativum and Glycine max assayed in the presence of saturating Ca2+ was markedly inhibited by the exopolysaccharides (EPS) of their symbiotic-partners, Rhizobium leguminosarum and Bradyrhizobium japonicum, respectively. Excess concentrations of Ca2+ did not alter inhibition by EPS. EPS of Bradyrhizobium japonicum was the most effective inhibitor, but the reduction in glucan synthase activity was not host specific. Two other polyglucans of non-symbiotic organisms, xanthan and laminarin, exhibited no influence on the enzyme. The effects are discussed with regard to the function of EPS in protecting rhizobia against plant defence reactions. © 1991.