Glufosinate

Last updated
Glufosinate
Glufosinate.png
Glufosinate zwitterion 3D ball.png
Names
Preferred IUPAC name
2-Amino-4-[hydroxy(methylphosphonoyl)]butanoic acid
Other names
Phosphinothricin
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.051.893 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 257-102-5
KEGG
PubChem CID
UNII
  • InChI=1S/C5H12NO4P/c1-11(9,10)3-2-4(6)5(7)8/h4H,2-3,6H2,1H3,(H,7,8)(H,9,10) Yes check.svgY
    Key: IAJOBQBIJHVGMQ-UHFFFAOYSA-N Yes check.svgY
  • O=P(O)(CCC(C(=O)O)N)C
Properties
C5H12NO4P
Molar mass 181.128 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Glufosinate (also known as phosphinothricin and often sold as an ammonium salt) is a naturally occurring broad-spectrum herbicide produced by several species of Streptomyces soil bacteria. Glufosinate is a non-selective, contact herbicide, with some systemic action. [1] Plants may also metabolize bialaphos and phosalacine, other naturally occurring herbicides, directly into glufosinate. [2] 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 and resulting in plant death. [3]

Contents

Discovery

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". [4] :90 They determined that phosphinothricin irreversibly inhibits glutamine synthetase. [4] :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. [4] :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 viridochromogenes was called "phosphinothricin acetyltransferase" or "pat". [4] :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. [4] :98

Use

Glufosinate use in the USA in 2018 Glufosinate USA 2018.png
Glufosinate use in the USA in 2018

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. [3] It is sold in formulations under brands including Basta, Rely, Finale, Challenge and Liberty. [3] Glufosinate is typically used in three situations as an herbicide:

Glufosinate also has shown to provide some protection against various plant diseases, as it also acts to kill fungi and bacteria on contact. [6]

Genetically modified crops

Genetically modified crops resistant to glufosinate were created by genetically engineering the bar or pat genes from streptomyces into the relevant crop seeds. [4] :98 [7] In 1995 the first glufosinate-resistant crop, canola, was brought to market, and it was followed by corn in 1997, cotton in 2004, and soybeans in 2011. [7]

Mode of action

Phosphinothricin is a glutamine synthetase inhibitor that binds to the glutamate site. Glufosinate-treated plants die due to a buildup of ammonia in the thylakoid lumen, leading to the uncoupling of photophosphorylation. [6] The uncoupling of photophosphorylation causes the production of reactive oxygen species, lipid peroxidation, and membrane destruction. [8]

Elevated levels of ammonia are detectable within one hour after application of phosphinothricin. [3]

Toxicity

Exposure to humans in foods

As glufosinate is often used as a pre-harvest desiccant, it can be found in foods that humans ingest. Such foods include potatoes, peas, beans, corn, wheat, and barley. In addition, the chemical can be passed to humans through animals who are fed contaminated straw. Flour processed from wheat grain that contained traces of glufosinate was found to retain 10-100% of the chemicals' residues. [9]

The herbicide is also persistent; it has been found to be prevalent in spinach, radishes, wheat and carrots that were planted 120 days after the treatment of the herbicide. [3] Its persistent nature can also be observed by its half-life which varies from 3 to 70 days depending on the soil type and organic matter content. [3] Residues can remain in frozen food for up to two years and the chemical is not easily destroyed by cooking the food item in boiling water. [9] The EPA classifies the chemical as 'persistent' and 'mobile' based on its lack of degradation and ease of transport through soil. A study revealed the presence of circulating PAGMF in women with and without pregnancy, paving the way for a new field in reproductive toxicology including nutrition and utero-placental toxicities [10]

Exposure limits

There are no exposure limits established by the Occupational Safety & Health Administration or the American Conference of Governmental Industrial Hygienists. [11] The WHO/FAO recommended acceptable daily intake (ADI) for glufosinate is 0.02 mg/kg. [9] The European Food Safety Authority has set an ADI of 0.021 mg/kg. The Acute reference dose (ARfD) for child-bearing women is 0.021 mg/kg. [9]

Regulation

Glufosinate is a United States Environmental Protection Agency EPA registered chemical. It is also a California registered chemical. It is not banned in the country and it is not a PIC pesticide. [12] There are no exposure limits established by OSHA or the American Conference of Governmental Industrial Hygienists. [11]

Glufosinate is not approved for use as an herbicide in Europe; it was last reviewed in 2007 and that registration expired in 2018. [13] It has been withdrawn from the French market since October 24, 2017 by the Agence nationale de sécurité sanitaire de l'alimentation, de l'environnement et du travail due to its classification as a possible reprotoxic chemical (R1b). [14]

Related Research Articles

<span class="mw-page-title-main">Herbicide</span> Type of chemical used to kill unwanted plants

Herbicides, also commonly known as weed killers, are substances used to control undesired plants, also known as weeds. Selective herbicides control specific weed species while leaving the desired crop relatively unharmed, while non-selective herbicides kill plants indiscriminately. The combined effects of herbicides, nitrogen fertilizer, and improved cultivars has increased yields of major crops by 3x to 6x from 1900 to 2000.

<span class="mw-page-title-main">Pesticide resistance</span> Decreased effectiveness of a pesticide on a pest

Pesticide resistance describes the decreased susceptibility of a pest population to a pesticide that was previously effective at controlling the pest. Pest species evolve pesticide resistance via natural selection: the most resistant specimens survive and pass on their acquired heritable changes traits to their offspring. If a pest has resistance then that will reduce the pesticide's efficacy – efficacy and resistance are inversely related.

<span class="mw-page-title-main">Glyphosate</span> Systemic herbicide and crop desiccant

Glyphosate is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP). It is used to kill weeds, especially annual broadleaf weeds and grasses that compete with crops. Its herbicidal effectiveness was discovered by Monsanto chemist John E. Franz in 1970. Monsanto brought it to market for agricultural use in 1974 under the trade name Roundup. Monsanto's last commercially relevant United States patent expired in 2000.

<span class="mw-page-title-main">Paraquat</span> Chemical compound used as an herbicide

Paraquat (trivial name; ), or N,N′-dimethyl-4,4′-bipyridinium dichloride (systematic name), also known as methyl viologen, is an organic compound with the chemical formula [(C6H7N)2]Cl2. It is classified as a viologen, a family of redox-active heterocycles of similar structure. This salt is one of the most widely used herbicides. It is quick-acting and non-selective, killing green plant tissue on contact. It is also toxic (lethal) to human beings and animals due to its redox activity, which produces superoxide anions. It has been linked to the development of Parkinson's disease and is banned in 58 countries.

<span class="mw-page-title-main">Glutamate dehydrogenase</span> Hexameric enzyme

Glutamate dehydrogenase is an enzyme observed in both prokaryotes and eukaryotic mitochondria. The aforementioned reaction also yields ammonia, which in eukaryotes is canonically processed as a substrate in the urea cycle. Typically, the α-ketoglutarate to glutamate reaction does not occur in mammals, as glutamate dehydrogenase equilibrium favours the production of ammonia and α-ketoglutarate. Glutamate dehydrogenase also has a very low affinity for ammonia, and therefore toxic levels of ammonia would have to be present in the body for the reverse reaction to proceed. However, in brain, the NAD+/NADH ratio in brain mitochondria encourages oxidative deamination. In bacteria, the ammonia is assimilated to amino acids via glutamate and aminotransferases. In plants, the enzyme can work in either direction depending on environment and stress. Transgenic plants expressing microbial GLDHs are improved in tolerance to herbicide, water deficit, and pathogen infections. They are more nutritionally valuable.

<span class="mw-page-title-main">Clavulanic acid</span> Molecule used to overcome antibiotic resistance in bacteria

Clavulanic acid is a β-lactam drug that functions as a mechanism-based β-lactamase inhibitor. While not effective by itself as an antibiotic, when combined with penicillin-group antibiotics, it can overcome antibiotic resistance in bacteria that secrete β-lactamase, which otherwise inactivates most penicillins.

A biopesticide is a biological substance or organism that damages, kills, or repels organisms seen as pests. Biological pest management intervention involves predatory, parasitic, or chemical relationships.

<span class="mw-page-title-main">Genetically modified crops</span> Plants used in agriculture

Genetically modified crops are plants used in agriculture, the DNA of which has been modified using genetic engineering methods. Plant genomes can be engineered by physical methods or by use of Agrobacterium for the delivery of sequences hosted in T-DNA binary vectors. In most cases, the aim is to introduce a new trait to the plant which does not occur naturally in the species. Examples in food crops include resistance to certain pests, diseases, environmental conditions, reduction of spoilage, resistance to chemical treatments, or improving the nutrient profile of the crop. Examples in non-food crops include production of pharmaceutical agents, biofuels, and other industrially useful goods, as well as for bioremediation.

<span class="mw-page-title-main">Glutamine synthetase</span> Class of enzymes

Glutamine synthetase (GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

<span class="mw-page-title-main">Agricultural chemistry</span> Agricultural sub-discipline of applied chemistry

Agricultural chemistry is the chemistry, especially organic chemistry and biochemistry, as they relate to agriculture. Agricultural chemistry embraces the structures and chemical reactions relevant in the production, protection, and use of crops and livestock. Its applied science and technology aspects are directed towards increasing yields and improving quality, which comes with multiple advantages and disadvantages.

Roundup Ready is the Monsanto trademark for its patented line of genetically modified crop seeds that are resistant to its glyphosate-based herbicide, Roundup.

LibertyLink is a BASF-owned brand of genes for use in agriculture providing tolerance to Liberty herbicide and glufosinate. The genes were developed by Bayer CropScience, before being sold to BASF Ag in late 2017. LibertyLink provides an herbicide resistance system that is still effective in the presence of glyphosate resistant weeds. The gene which gives resistance to glufosinate is a bar or pat gene which was first isolated from two species of Streptomyces bacteria. Glufosinate was included in a biocide ban proposed by the Swedish Chemicals Agency and approved by the European Parliament on January 13, 2009.

<span class="mw-page-title-main">Bialaphos</span> Chemical compound

Bialaphos is a natural herbicide produced by the bacteria Streptomyces hygroscopicus and Streptomyces viridochromogenes. It is also known by the ISO common name bilanafos. Bialaphos is a protoxin and nontoxic as is. When it is metabolized by a plant, the glutamic acid analog glufosinate is released which inhibits glutamine synthetase. This results in the accumulation of ammonium and disruption of primary metabolism.

<span class="mw-page-title-main">EPSP synthase</span> Enzyme produced by plants and microorganisms

5-enolpyruvylshikimate-3-phosphate (EPSP) synthase is an enzyme produced by plants and microorganisms. EPSPS catalyzes the chemical reaction:

4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors are a class of herbicides that prevent growth in plants by blocking 4-Hydroxyphenylpyruvate dioxygenase, an enzyme in plants that breaks down the amino acid tyrosine into molecules that are then used by plants to create other molecules that plants need. This process of breakdown, or catabolism, and making new molecules from the results, or biosynthesis, is something all living things do. HPPD inhibitors were first brought to market in 1980, although their mechanism of action was not understood until the late 1990s. They were originally used primarily in Japan in rice production, but since the late 1990s have been used in Europe and North America for corn, soybeans, and cereals, and since the 2000s have become more important as weeds have become resistant to glyphosate and other herbicides. Genetically modified crops are under development that include resistance to HPPD inhibitors. There is a pharmaceutical drug on the market, nitisinone, that was originally under development as an herbicide as a member of this class, and is used to treat an orphan disease, type I tyrosinemia.

<span class="mw-page-title-main">Crop desiccation</span>

Pre-harvest crop desiccation refers to the application of an agent to a crop just before harvest to kill the leaves and/or plants so that the crop dries out from environmental conditions, or "dry-down", more quickly and evenly. In agriculture, the term desiccant is applied to an agent that promotes dry down, thus the agents used are not chemical desiccants, rather they are herbicides and/or defoliants used to artificially accelerate the drying of plant tissues. Desiccation of crops through the use of herbicides is practiced worldwide on a variety of food and non-food crops.

The Enlist Weed Control System is an agricultural system that includes seeds for genetically modified crops that are resistant to Enlist and the Enlist herbicide; spraying the herbicide will kill weeds but not the resulting crop. The system was developed by Dow AgroSciences, part of Dow Chemical Company. In October 2014 the system was registered for restricted use in Illinois, Indiana, Iowa, Ohio, South Dakota and Wisconsin by the US Environmental Protection Agency. In 2013, the system was approved by Canada for the same uses.

<span class="mw-page-title-main">DMH-11 Mustard</span> Genetically modified variety of mustard plant

Dhara Mustard Hybrid-11, otherwise known as DMH - 11, is a genetically modified hybrid variety of the mustard species Brassica juncea. It was developed by Professor Deepak Pental from the University of Delhi, with the aim of reducing India's demand for edible oil imports. DMH - 11 was created through transgenic technology, primarily involving the Bar, Barnase and Barstar gene system. The Barnase gene confers male sterility, while the Barstar gene restores DMH - 11's ability to produce fertile seeds. The insertion of the third gene Bar, enables DMH - 11 to produce phosphinothricin-N- acetyl-transferase, the enzyme responsible for Glufosinate resistance. This hybrid mustard variety has come under intense public scrutiny, mainly due to concerns regarding DMH - 11's potential to adversely affect the environment as well as consumer health. DMH - 11 was found not to pose any food allergy risks, and has demonstrated increased yields over existing mustard varieties. Conflicting details and results regarding the field trials and safety evaluations conducted on DMH - 11 have delayed its approval for commercial cropping.

<span class="mw-page-title-main">Fluazifop</span> ACCase herbicide, fop, anti-grass

Fluazifop is the common name used by the ISO for an organic compound that is used as a selective herbicide. The active ingredient is the 2R enantiomer at its chiral centre and this material is known as fluazifop-P when used in that form. More commonly, it is sold as its butyl ester, fluazifop-P butyl with the brand name Fusilade.

References

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  2. Schwartz, D.; Berger, S.; Heinzelmann, E.; Muschko, K.; Welzel, K.; Wohlleben, W. (2004). "Biosynthetic Gene Cluster of the Herbicide Phosphinothricin Tripeptide from Streptomyces viridochromogenes Tu494". Applied and Environmental Microbiology. 70 (12): 7093–7102. Bibcode:2004ApEnM..70.7093S. doi:10.1128/AEM.70.12.7093-7102.2004. PMC   535184 . PMID   15574905.
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  7. 1 2 Green JM and Castle LA. Transitioning from Single to Multiple Herbicide-resistant Crops. Chapter 4 in Glyphosate Resistance in Crops and Weeds: History, Development, and Management. Editor, Vijay K. Nandula. John Wiley & Sons, 2010 ISBN   9781118043547 Page 112
  8. Summary of Herbicide Mechanism of Action, HRAC and WSSA
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  10. Aris, Aziz; Leblanc, Samuel (2011). "Maternal and fetal exposure to pesticides associated to genetically modified foods in Eastern Townships of Quebec, Canada". Reproductive Toxicology. 31 (4): 528–533. doi:10.1016/j.reprotox.2011.02.004. PMID   21338670. S2CID   16144327.
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  12. "The Rotterdam Convention on Prior Informed Consent (PIC)". Archived from the original on 2021-09-24. Retrieved 2015-08-07.
  13. European Commission. Glufosinate in EU Pesticides Database Page accessed August 7, 2015
  14. Anses. L’Anses procède au retrait de l’autorisation de mise sur le marché du Basta F1, un produit phytopharmaceutique à base de glufosinate Page accessed October 26, 2017