Contents of isoflavones and effect of isoflavones on root hair curling in non-nodulating-Rj1Rj1) soybean plant

Abstract

Abstract Leguminous plants form symbiotic nitrogen-fixing nodules with specific bacterial species of Rhizobium or Bradyrhizobium. This symbiosis takes place by interaction of both partners. The non-nodulating mutants of the host plants are useful materials for physiological and genetical analyses of plant function in nodule formation. In a Rj 1 non-nodulating mutant of soybean, root hair curling was greatly reduced, whereas bacterial adhesion onto the root surface was not affected as compared to the nodulating soybean (Suganuma et al. 1990). Recently, plant flavonoids have been identified as specific-signals inducing the expression of Rhizobium nod ABC genes responsible for root hair curling (Firmin et al. 1986; Peters et al. 1986; Djordjevic et al. 1987; Zaat et al. 1987). The flavonoid secreted by the plant interacts with the product of the nodD gene which is constitutively expressed in the microsymbiont and induces the expression of several nodulation genes including the nod ABC genes (Rolfe and Gresshoff 1988). In the soybean/Bradyrhizobium symbiosis, two inducing compounds were isolated from soybean seedlings and were identified as 4,7-dihydroxyisoflavone (daidzein) and 4,5,7-trihydroxyisoflavone (genistein) (Kosslak et al. 1987). In the present study, we determined whether the lack of root hair curling in the Rj 1 soybean mutant was due to the absence or reduced contents of isoflavones.