Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2002
Publication Date: 1/5/2003
Citation: Duke, S.O., Rimando, A.M., Pace, P.F., Reddy, K.N., Smeda, R.J. 2003. Isoflavone, Glyphosate, and Aminomethylphosphonic Acid Levels in Seeds of Glyphosate-treated, Glyphosate-resistant Soybean. Journal of Agricultural and Food Chemistry. 51(1):340-344. Interpretive Summary: A study was conducted at two locations (Mississippi and Missouri) to determine if the herbicide glyphosate influences estrogenic isoflavone levels in glyphosate-resistant (GR) soybeans. The seed of GR-soybeans had normal levels of isoflavones at harvest whether treated with glyphosate early or late or whether they were treated with other herbicides. Seeds of GR-soybeans treated at the blooming stage had the highest levels of glyphosate and its degradation product, aminomethylphosphonic acid. Seeds of plants treated earlier had much lower levels of these compounds. The highest levels of glyphosate found were below EPA tolerance levels.
Technical Abstract: The estrogenic isoflavones of soybeans and their glycosides are products of the shikimate pathway, the target pathway of glyphosate. We tested the hypothesis that non-phytotoxic levels of glyphosate and other herbicides known to affect phenolic compound biosynthesis might influence levels of these nutraceutical compounds in soybeans. The effects of glyphosate and other herbicides were determined on estrogenic isoflavones and shikimate in glyphosate-resistant soybeans from identical experiments conducted in 2000 with different cultivars in Mississippi and Missouri. Four commonly-used herbicide treatments were compared to a hand-weeded control. The herbicide treatments were: (1) Glyphosate at 1260 g/ha at 3 WAP (wk after planting), followed by glyphosate at 840 g/ha at 6 WAP; (2) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied PRE (preemergence), followed by glyphosate at 1260 g/ha at 6 WAP; (3) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied PRE, followed by glyphosate at 1260 g/ha at full bloom; and (4) sulfentrazone at 168 g/ha plus chlorimuron at 34 g/ha applied PRE, followed by acifluorfen at 280 g/ha plus bentazon at 560 g/ha plus clethodim at 140 g/ha at 6 WAP. Soybeans were harvested at maturity and seeds were analyzed for daidzein, daidzin, genistein, genistin, glycitin, glycitein, shikimate, glyphosate, and the glyphosate degradation product, aminomethylphosphonic acid (AMPA). There were no remarkable effects of any treatment on the contents of any of the biosynthetic compounds in soybean seed from either test site, indicating that early and later season applications of glyphosate have no effects on phytoestrogen levels in glyphosate-resistant soybeans. Glyphosate and AMPA residues were highest in seeds from treatment 3 than the other two treatments in which glyphosate was used earlier. Low levels of glyphosate and AMPA were found in treatment 4 and a hand-weeded control, apparently due to herbicide drift.