Changes in Amounts of Isoflavones in Seeds during Germination of Soybean and Role in the Formation of Root Nodules

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Changes in the amounts of daidzein and genistein, which induce the activation of nodulation genes in Bradyrhizobium japonicum, during the germination of soybean (Glycine max (L.) Merr.) seeds were investigated. The amount of daidzein and genistein in the dry seeds decreased rapidly during imbibition. In the seedings, the amounts of isoflavones were much larger in the cotyledons than in the roots or hypocotyls. The amount of both isoflavones exuded from the seeds were very low compared with those in he seeds. Daidzein and genistein exuded from the cotyledons accounted for 76 and 43% of the total amount of each compound exuded from the seedlings, respectively. Although inoculation with B. Japonicum hardly affected the amounts of isoflavones in the seedlings, the amount of daidzein exuded from the seedings tended to be reduced by the inoculation. These results suggest that at the initial stages of nodulation, the cotyledonary tissues of the seeds or the seedings are a major source of isoflavones in the rhizosphere. The correlation between the amounts of isoflavones in seeds and the number of nodules formed on roots was analyzed in various cultivars of soybean. However, there was no clear relationship between these two parameters in any of the cultivars examined.
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