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glyphosate N-(phosphonomethyl)glycine: a herbicide, marketed as Roundup and Tumbleweed, that kills a wide range of plants but shows little persistence in soil and has low toxicity to animals. If applied to the leaves it is rapidly translocated to the rest of the plant, and hence can penetrate the roots of even hardy perennials. It works by blocking the synthesis of aromatic amino acids, so that treated plants are unable to manufacture proteins and other key metabolites. Glyphosate inhibits the activity of 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS), a key enzyme in the shikimic acid pathway, which occurs only in plants and microorganisms. Certain crops, notably soya bean, have been genetically engineered to give them resistance to glyphosate, by inserting genes for an EPSPS enzyme from Agrobacterium. These ‘Roundup-ready’ crops, which can be sprayed with the herbicide without being affected, are now widely grown in North America and elsewhere.