CHANGES IN AMOUNTS OF ISOFLAVONES IN SEEDS DURING GERMINATION OF SOYBEAN AND ROLE IN THE FORMATION OF ROOT-NODULES

Changes in the amounts of daidzein and genistein, which induce the act ivation of nodulation genes in Bradyrhizobium japonicum, during the ge rmination of soybean (Glycine max (L.) Merr.) seeds were investigated. The amounts of daidzein and genistein in the dry seeds decreased rapi dly during imbibition. In the seedlings, the amounts of isoflavones we re much larger in the cotyledons than in the roots or hypocotyls. The amounts of both isoflavones exuded from the seeds were very low compar ed with those in the seeds. Daidzein and genistein exuded from the cot yledons 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 seedlings tended to be reduce d by the inoculation. These results suggest that at the initial stages of nodulation, the cotyledonary tissues of the seeds or the seedlings 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.