Production of Cell-Associated Polysaccharides of Rhizobium fredii USDA205 Is Modulated by Apigenin and Host Root Extract. Bradley L. Reuhs. Complex Carbohydrate Research Center, University of Georgia, 220 Riverbend Road, Athens 30602-4712 U.S.A. John S. Kim, Allison Badgett, and Russell W. Carlson. Complex Carbohydrate Research Center, University of Georgia, 220 Riverbend Road, Athens 30602-4712 U.S.A. MPMI 7:240-247. Accepted 4 January 1994. Copyright 1994 The American Phytopathological Society.

Rhizobium fredii USDA205 cells were cultured in the presence of 4',5,7-trihydroxyflavone (apigeniu), a compound that has been shown lo induce the nod genes and other symbiosis-related genes in R. fredii. The cell-associated polysaccharides were then extracted with hot phenol/ water, separated by repetitive gel nitration chromatography, and analyzed by polyacrylamide gel electrophoresis, nuclear magnetic resonance spectrometry, high-performance anion-exchange chromatography, and gas chromatography. These analyses showed that apigenin effects a modulation in the production of some cell-associated bacterial polysaccharides: 1) The production of a glucan is severely attenuated; 2) the lipopolysaccharide O antigen is modified in composition and Mr distribution; and 3) the ratio of two extracted polysaccharides, which are structurally analogous to group II K antigens (cap-sular polysaccharides), is altered. Similar effects resulted from the inclusion of host plant root extract in the growth medium.