|Miller K J|
|Hadley J A|
|Gustine D L|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/1993
Publication Date: N/A
Interpretive Summary: New research findings are helping scientists understand how soil bacteria (Rhizobium and Bradyrhizobium) are able to find their way into leguminous plant roots. The roots provide nutrients for the bacteria to grow, while the bacteria convert nitrogen from the air to a chemically reduced form that serves as a critical nutrient to the crop plant (this mutually beneficial life style is called symbiosis). Extending the bacteria host range to grasses and increasing the efficiency of nitrogen fixation in legumes is of great importance to agriculture. Adequate supply of nitrogen to field crops in this way, translates to reduced petroleum energy input for fertilizer production. Results to be reported in the journal Plant Physiology, show that cyclic beta-1,6-1,3 glucans (a polymer of the carbohydrate glucose) are synthesized by Bradyrhizobium japonicum, and that they function biologically in stimulating biosynthesis of isoflavonoids in the host plant. Since isoflavonoids are known to be molecular signals for stimulating growth of the bacteria in plant roots, these findings are expected to help unravel the mysteries of symbiosis and nitrogen fixation.
Technical Abstract: High levels of cyclic beta-1,6-1,3 glucans (eg. 0.1 mg/mg total protein) are synthesized by free-living cells as well as by bacteroids of Bradyrhizobium japonicum USDA 110 (Miller, K.J. et al., 1990, J. Bacteriol. 172:136-142; Gore, R.S. and Miller, K.J., 1993, Plant Physiol. 102:191-194). These molecules share structural features with glucan fragments isolated from the mycelial cell wall of the soybean pathogen Phytophthora megasperma. These latter glucans have been shown to be potent elicitors of isoflavonoid production in Glycine max. Using the well-characterized soybean cotyledon bioassay, we now show that the cyclic beta-1,6-1,3 glucans of B. japonicum USDA 110 are also biologically-active elicitors of isoflavonoid production.