CYCLIC BETA-1,6-1,3-GLUCANS OF BRADYRHIZOBIUM-JAPONICUM USDA-110 ELICIT ISOFLAVONOID PRODUCTION IN THE SOYBEAN (GLYCINE-MAX) HOST

High levels of cyclic beta-1,6-1,3-glucans (e.g. 0.1 mg mg(-1) of tota l protein) are synthesized by free-living cells as well as by bacteroi ds of Bradyrhizobium japonicum USDA 110 (K.J. Miller, R.S. Gore, R. Jo hnson, AJ. Benesi, V.N. Reinhold [1990] J Bacteriol 172: 136-142; R.S. Core and KJ. Miller [1993] Plant Physiol 102: 191-194). These molecul es share structural features with glucan fragments isolated from the m ycelial cell wall of the soybean (Glycine max) pathogen Phytophthora m egasperma. These latter glucans have been shown to be potent elicitors (at nanogram levels) of the phytoalexin glyceollin in G. max. Using t he well-characterized soybean cotyledon bioassay, we now show that the cyclic beta-1,6-1,3-glucans of B. japonicum USDA 110 are also biologi cally active elicitors of glyceollin production (but at microgram leve ls). We further show that both classes of beta-glucans elicit the prod uction of the isoflavone daidzein within soybean cotyledon wound dropl ets.