Studies on the physiological mechanisms of isoflavonoids on the nod-gene expression of Bradyrhizobium japonicum

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In order to investigate the point shared into ineffective or effective root nodules when soybean cultivars harboring Rj-gene were inoculated with a compatible or incompatible strain, we analyzed anatomically the nodule development in the roots of Rj_2Rj_3-and Rj_4-genotype soybean, CNS and Hill respectively, infected by Bradyrhizobium japonicum strains Is-1 (incompatible to CNS and compatible to Hill) and Is-34 (compatible to CNS and incompatible to Hill). The root hairs curlings were assayd by the staining method with methylene blue, the cortex divisions were examined with a light microscope, the invitation of rhizobia were investigated by the fluorescent antibody of rhizobia strains Is-1 or Is-34 with a fluorescence microscope. These results showed that the restriction mechanism of the infection with incompatible strains might operate at the step of rhizobia invasion into the primary meristem directly under cortex within 5 days after sowing and inoculation.On the assumption that the … More various composition of isoflavonoids were different in those soybean roots and the species of nod metabolites produced by genistein, daidzein and the root extracts were different among rhizobia strains, we searched a signal molecular which operate at the point shared intoineffective or effective root nodules. Daizein and glyceollin I contents in those soybean roots were level up to 7 days. Also the roots of CNS and Hill of 3 and 5 days' seedling inoculated with Is-1 or Is-34 were no difference in the contects of genistein and daidzen known as main isoflavonoids which induced the nod-gene expression of rhizobia. However a specific fluorescent spot was identified in the root extract of Hill and not in that of CNS.In order to analyze the composition and amount of nod metabolites, Is-1 and Is-34 were incubated using ^<14>C-acetate as tracer with genistein, daidzein, each soybean root extract or a specific fluorescent spot of Hill. These results shown that the separation pattern of nod metabolites of Is-1 or Is-34 were little difference among each treatment, but in comparison between Is-1 or Is-34, the number and intensity of nod metabolites were large difference. The chitinase treatment of those nod metabolites decreased the number of nod metabolites, thus it was confirmed that nod factors were included those nod metabolites. Hence, it was the different composition of nod metabolites between strains determined the compatibility of soybean varieties and B.japonicum strains, through different responses of host plant roots to nod metabolites. Less