SPECIFIC FLAVONOIDS PROMOTE INTERCELLULAR ROOT COLONIZATION OF ARABIDOPSIS-THALIANA BY AZORHIZOBIUM-CAULINODANS ORS571

The ability of Azorhizobium caulinodans ORS571 and other diazotrophic bacteria to Internally colonize roots of Arabidopsis thaliana has been studied, Strains tagged with lacZ or gusA reporter genes were used, a nd the principal colonization sites were found to be the points of eme rgence of lateral roofs, lateral root cracks (LRCs), High frequencies of colonization were found; 63 to 100% of plants were colonized by ORS 571, and 100% of plants were colonized by Herbaspirillum seropedicae, After LRCs were colonized, bacteria moved into intercellular spaces be tween the cortical and endodermal cell layers, Specific flavonoids, na ringenin and daidzein, at 5 x 10(-5) M, significantly promoted coloniz ation by ORS571, By using a nodC and a nodD mutant of ORS571, it was s hown that neither Nod factors nor NodD are involved in colonization or flavonoid stimulation of colonization, Flavonoids did not appear to b e stimulating LRC colonization by their activity as nutritional factor s, LRC acid intercellular colonization by H. seropedicae was stimulate d by naringenin and daidzein at the same concentration that stimulated colonization by ORS571.