7,4'-Dihydroxyflavanone Is the Major Azorhizobium nod Gene-Inducing Factor Present in Sesbania rostrata Seedling Exudate. Eric Messens. Laboratorium voor Genetica, Rijksuniversiteit Gent, B-9000 Gent, Belgium. Danny Geelen, Marc Van Montagu, and Marcelle Holsters. Laboratorium voor Genetica, Rijksuniversiteit Gent, B-9000 Gent, Belgium.. MPMI 4:262-267. Accepted 25 January 1991. This article is in the public domain and not copryightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991.

Exudate from Sesbania rostrata seedlings contains signaling compounds that induce the common nodABC operon of the bacterial symbiont Azorhizobium caulinodans ORS571. An Azorhizobium strain harboring a nodA::lacZ reporter fusion was used to monitor the nod-inducing activity of crude exudate fractions that were separated by reversed-phase chromatography. The major inducer was shown, by spectroscopic analysis and by comparison with chemically synthesized compounds, to be 7,4'-dihydroxyflavanone (liquiritigenin). Newly synthesized analogues, 7,3'-dihydroxyflavanone and 7.2' dihydroxyflavanone, have only poor inducing activity.