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Glyphosate (N-(phosphonomethyl) glycine, C₃H₈NO₅P) is a non-selective herbicide to kill weeds, especially perennials.

Glyphosate is the primary ingredient in Monsanto's popular herbicide Roundup. Many crops have been genetically engineered to be resistant to it. The chemical is only absorbed by the leaves of planst and it is not absorbed by roots from the soil.

Chemistry

Glyphosate is an aminophosphonic analogue of the natural amino acid glycine and the name is a contraction of glycine, phospho-, and -ate: Chemical structure of glyphosate.

Biochemistry

Glyphosate kills plants by inhibiting the enzyme 5-enolpyruvoyl-shikimate-3-phosphate synthetase (EPSPS), which forms the aromatic amino acids: phenylalanine, tyrosine and tryptophan. EPSPS catalyzes the reaction of Shikimate-3-phosphate (S3P) and phosphoenolpyruvate (PEP) to form EPSP and phosphate. The aromatic amino acids are also used to make secondary metabolites such as folates, ubiquinones and naphthoquines. The shikimate pathway is not present in mammals and humans.

Environmental science

Glyphosate binds tightly to soil so it does not end up passing through the soil and ending up in the aquifers. It is rapidly metabolized in the soil by dephosphorolization.

Health concerns

There are concerns about the effects of glyphosate (and Roundup) on non-plant species. For more information, see the Roundup article.

Glyphosate resistance

Some microorganisms have a version of 5-enolpyruvoyl-shikimate-3-phosphate synthetase (EPSPS) that is resistant to glyphosate inhibition. The version used in genetically modified crops was isolated from Agrobacterium strain CP4 (CP4 EPSPS) that was resisitant to glyphosate. The CP4 EPSPS gene was cloned and inserted into soybeans. The CP4 EPSPS gene was engineered for plant expression by fusing the 5' end of the gene to a chloroplast transit peptide derived from the petunia EPSPS. This transit peptide was used because it had shown previously an ability to deliver bacterial EPSPS to the chloroplasts of other plants. The plasmid used to move the gene into soybeans was PV-GMGTO4. It contained three bacterial genes, two PC4 EPSPS genes, and a gene encoding B-glucuronidase (GUS) from E-coli as a marker. The DNA was injected into the soybeans using the particle acceleration method. Soybean cultivar A54O3 was used for the transformation. The expression of the GUS gene was used as the initial evidence of transformation. Gus expression was detected by a staining method in which the GUS enzyme converts a substrate into a blue precipitate. Those plants that showed GUS expression were then taken and sprayed with glyphosate and their tolerance was tested over many generations.

Genetically modifies crops

In 1991, genetically modified soybeans were available commercially. This greatly improved the ability to control weeds in soybean fields since glyphosate could be sprayed on fields without hurting the crop. As of 2004, glyphosate was used on 80% of U.S. soybean fields to eliminate weeds.

Tradenames

It was first sold by Monsanto under the tradename Roundup but is no longer under patent so is now marketed under various names.

Trivia

Glyphosate is one of a number of herbicides used by the United States government to spray Colombian coca fields through Plan Colombia. Its health effects, effects on legal crops, and effectiveness in fighting the war on drugs have been widely disputed.

External Links

• US weighs costs of Plan Colombia
• Study Showing Glyphosate to Be Dangerous
• Website of the SynBioC research group, working on different types of aminophosphonates

• Herbicides