The estrogenic isoflavones found in soybeans and their glycosides are products of the shikimate pathway that is targeted by glyphosate, a common soybean herbicide. This study was to test whether nonphytotoxic levels of glyphosate and other herbicides that affect phenolic biosynthesis might influence levels of these isoflavones in glyphosate-resistance (Roundup Ready™) soybeans. Four herbicide treatments were applied to soybeans at different times and rates at two locations; the soybeans were harvested and the seed analyzed for daidzein, daidzin, genistein, genistin, glycitein, shikimate, glyphosate and glyphosate degradation compounds. The results indicated no treatment effect on the content of any of these biosynthetic compounds in the soybean seed from either the Mississippi or Missouri test site, indicating that the early season and later season applications of glyphosate had no effect on the phytoestrogen level in glyphosate-resistant soybeans. (This study should eliminate concern about isoflavone levels in Roundup Ready™ soybean varieties).
Duke, S.O. and co-workers. 2003. Isoflavone, glyphosate and aminomethylphosphonic acid levels in seeds of glyphosate-treated, glyphosate-resistant soybean. J. Agri. and Food Chem. 51(1): 340-344.