Glufosinate

Glufosinate (also known as phosphinothricin and often sold as an ammonium salt) is a naturally occurring broad-spectrum systemic herbicide produced by several species of Streptomyces soil bacteria. Plants may also metabolize bialaphos, another naturally occurring herbicide, directly into glufosinate. The compound irreversibly inhibits glutamine synthetase, an enzyme necessary for the production of glutamine and for ammonia detoxification, giving it antibacterial, antifungal and herbicidal properties. Application of glufosinate to plants leads to reduced glutamine and elevated ammonia levels in tissues, halting photosynthesis, resulting in plant death. Glufosinate (also known as phosphinothricin and often sold as an ammonium salt) is a naturally occurring broad-spectrum systemic herbicide produced by several species of Streptomyces soil bacteria. Plants may also metabolize bialaphos, another naturally occurring herbicide, directly into glufosinate. The compound irreversibly inhibits glutamine synthetase, an enzyme necessary for the production of glutamine and for ammonia detoxification, giving it antibacterial, antifungal and herbicidal properties. Application of glufosinate to plants leads to reduced glutamine and elevated ammonia levels in tissues, halting photosynthesis, resulting in plant death. In the 1960s and early 1970s, scientists at University of Tübingen and at the Meiji Seika Kaisha Company independently discovered that species of Streptomyces bacteria produce a tripeptide they called bialaphos that inhibits bacteria; it consists of two alanine residues and a unique amino acid that is an analog of glutamate that they named 'phosphinothricin'.:90 They determined that phosphinothricin irreversibly inhibits glutamine synthetase.:90 Phosphinothricin was first synthesized by scientists at Hoechst in the 1970s as a racemic mixture; this racemic mixture is called glufosinate and is the commercially relevant version of the chemical.:91–92 In the late 1980s scientists discovered enzymes in these Streptomyces species that selectively inactivate free phosphinothricin; the gene encoding the enzyme that was isolated from Streptomyces hygroscopicus was called the 'bialaphos resistance' or 'bar' gene, and the gene encoding the enzyme in Streptomyces viridochromeogenes was called 'phosphinothricin acetyltransferase' or 'pat'.:98 The two genes and their proteins have 80% homology on the DNA level and 86% amino acid homology, and are each 158 amino acids long.:98 Glufosinate is a broad-spectrum herbicide that is used to control important weeds such as morning glories, hemp sesbania (Sesbania bispinosa), Pennsylvania smartweed (Polygonum pensylvanicum) and yellow nutsedge similar to glyphosate. It is applied to young plants during early development for full effectiveness. It is sold in formulations under brands including Basta, Rely, Finale, Challenge and Liberty.