EFFECT OF AUTHENTIC FLAVONOIDS AND THE EXUDATE OF CLOVER ROOTS ON GROWTH-RATE AND INDUCING ABILITY OF NOD GENES OF RHIZOBIUM-LEGUMINOSARUM BV TRIFOLII

A number of authentic flavonoids and exudate of sprouted seeds of Trif olium pratense were used to test the growth rate and nodC:-:lacZ expre ssion controlled by nodD gene in Rhizobium leguminosarum bv. trifolii strains 24.1 and 288. All commercial flavonoids and clover exudate inc reased the growth rate of fresh field isolate 288 in defined minimal m edium. Apigenin and exudate inhibited the growth of laboratory strain 24.1. There was no correlation between the inducing activity and the g rowth rate of R. leguminosarum bv. trifolii strains. Unsubstituted fla vone, quercetin, hesperetin and hesperidin were not active in the indu ction of nodC-gene expression. Biological activity of aglycones and gl ycosides depended on their chemical structure i.e. quercetin-3-O-glyco side was more active than its aglycone, but hesperetin-7-O-glycoside w as not active similarly to hesperetin. These results suggest that the presence of the mixture of flavonoids in the exudate of the germinatin g seeds of clover can influence rhizobial population. Biological activ ity of flavonoids, measured by level of induction of beta-galactosidas e, depended on the structure of the compounds and also rhizobial strai n tested.