Rhizobial Nod-Gene Induction By Released Signal form Host Plant

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The inducing effects of flavonoids on the lebel of nod gene transcription were examined. The expression induction was measured the beta-galactosidase activity in Rhizobium leguminosarum bv. trifolii H1 (nod218) which is introduced a fusion plasmid (pMudI 1734) including lacZ, into nodA poeron of R. bv. trifolii into Sym plasmid cured strain H1(Nod^-).Four flavonoids (7-hydroxyflavone, 7HF ; 4', 7-dihydroxyflavone, DHF : 4', 5, 7-trihydroxyflavone, apigenic ; 3', 4, 5, 7-tetrahydroxyflavone, luteolin) were tested for nod inducing activity. The beta-galactosidase activity of strain H1(nod218) was transiently expressed only in early logarithmic phase of its growth stages. All of them were effective on the lacZ expression at the same lebel. The maximum infection of bete-galactiosidase activity was caused by 5 mu M of flavonoid addition.The induction of nodA : : lacZ expression of strain H1(nod28) wes also detected with an exudate form intact seedidilings of Trifulium repens cv. Ladino (1-5 days afyer seeding).Moreover, the influences of flavonoids in the rhizosphere on in the rhizosphre on infection thread formation was also observed.