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Unintended Effects of Genetic Manipulation
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Glyphosate-resistant soybeans have altered root nodules when sprayed with glyphosate.

Manipulated Organism: Soybean (Glycine max).

Inserted Transgenes: CP4 EPSPS gene cloned from Agrobacterium, which produces an herbicide-resistant version of the enzyme targeted by the herbicide glyphosate (Roundup).

Goal of This Study: Although glyphosate-resistant (GR) soybeans have a resistant form of the EPSPS enzyme, the symbiotic bacteria Bradyrhizobium japonicum that live in the soybean root nodules and fix nitrogen do not. The goal of this study was to determine whether glyphosate interferes with this symbiotic relationship.

Results of This Study:
  • In one greenhouse experiment, GR soybean root nodules increased in number but decreased in weight when plants were sprayed with glyphosate.
  • In a different experiment, root biomass and total nitrogen content decreased, in some cases by as much as 50%, when GR soybeans were sprayed with glyphosate.
  • In growth chamber experiments under water stress, root nodule activity (as measured by acetylene reduction) was lower when GR soybeans were sprayed with glyphosate. According to the authors, this enhanced sensitivity to water stress did not appear to be related to differences in transpiration.
Source: King, C. A., L. C. Purcell, and E. D. Vories (2001). "Plant growth and Nitrogenase Activity of Glyphosate-tolerant Soybean in Response to Foliar Glyphosate Applications," Agronomy Journal vol. 93, pp. 179-86.

Author Affiliations: University of Arkansas.

Funding: Not mentioned.

Product Status: Genetically modified, glyphosate-resistant soybeans have been grown commercially in the U.S. since 1996 and currently constitute 90% of the U.S. soybean crop.

Copyright 2009 The Nature Institute.

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