Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 2009
Publication Date: September 25, 2009
Citation: Bellaloui, N., Reddy, K.N., Zablotowicz, R.M., Abbas, H.K., Abel, C.A. 2009. Effects of Glyphosate Application on Seed Iron and Root Ferric (III) Reductase in Soybean Cultivars. Journal of Agriculture and Food Chemistry. 57:9569-9574 Interpretive Summary: Glyphosate is a nonselective broad-spectrum herbicide used extensively throughout the world for postemergence weed control. Soybean is a major crop in the world and soybean seed quality is determined by its protein, oil, and mineral contents. Iron is an essential nutrient for plant growth and development. Iron deficiency can be attributed to the consumption of food crops containing low levels of iron as a result of various soils and genetic factors. Recently, it was shown that iron deficiency had been increasingly observed in cropping systems with frequent glyphosate applications. We investigated the effect of glyphosate on iron assimilation using in vivo root ferric reductase (enzyme involved in iron assimilation) activity in glyphosate-sensitive (using drift rate) and resistant soybean (using commercial rate). Effect of commercial rate of glyphosate on seed iron concentration was also investigated in glyphosate-resistant soybean. The results showed a greater inhibition in iron concentration in leaves and ferric reductase activity in glyphosate-sensitive cultivar Hutchson than in glyphosate-sensitive cultivar DP5110. The inhibition of iron concentration in leaves and ferric reductase activity was noticed even in glyphosate-resistant cultivar AG 4604RR. These results indicate that glyphosate drift leads to reduction in iron concentration in seed and leaves, and in the activity of the enzyme ferric reductase in glyphosate-sensitive soybean. Identification of physiological and biochemical traits controlling iron nutrition in soybean seed will help soybean breeders select for higher mineral nutrition qualities.
Technical Abstract: Previous research demonstrated that nitrate assimilation and nitrogen fixation were significantly reduced by glyphosate (Gly) drift in glyphosate-susceptible (GS) soybean, but soybean had the ability to recover from the physiological stress caused by glyphosate drift. The objective of this study was to investigate the effects of Gly at drift rate (12.5 % of commercial use rate of 0.84 kg ai/ha) on iron (Fe) concentrations in seed, and Fe assimilation using root in vivo ferric reductase activity (FRA). A two-year field experiment and a greenhouse experiment were conducted. Results showed that Gly application resulted in a significant decrease in Fe concentration in seeds and in leaves compared to the non-treated plants (control). Fe concentration in leaves had significant positive correlations with root FRA (P<0.0001, r=0.806). A greater inhibition in Fe concentration in leaves and FRA was noticed in GS cultivar Hutchson than in GS cultivar DP5110. The inhibition of Fe concentration in leaves and FRA was noticed even in Gly-resistant (GR) cultivar AG 4604RR. These results indicate that Gly drift leads to reduction in Fe concentration in seed and leaves, and FRA in GS soybean. The positive correlation between Fe concentrations in leaves with FRA indicates that Fe status in leaves may determine FRA, and consequently Fe assimilation and concentration in seed. Identification of physiological and biochemical traits controlling Fe nutrition in soybean seed will help soybean breeders select for higher mineral nutrition qualities.