Aryl hydroxylation of diclofop by a cytochrome P450 dependent monooxygenase from wheat

McFadden, James J.; Frear, D.S.; Mansager, Eugene R.

doi:10.1016/0048-3575(89)90145-4

Cited by 78 publications

(45 citation statements)

References 23 publications

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“…Resistant crops metabolize diclofop by hydroxylation and subsequent conjugation to glucose. Diclofop hydroxylation was shown to be inhibited by tetcyclasis, an established Cyt P-450 inhibitor (20). Primsulfuron, a sulfonurea herbicide which inhibits plant acetohydroxyacid synthase in the branched chain amino acid pathway, was found to be hydroxylated in two different positions by maize seedling microsomes (7).…”

Section: Some Plant Cyt P-450 May Be Involved In Modification Of Herbmentioning

confidence: 99%

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Multiple Forms of Plant Cytochromes P-450

Donaldson¹,

Luster²

1991

Plant Physiol.

159

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Accumulating evidence indicates that there is a multiplicity of cytochrome P-450 enzymes in plants. These monooxygenases are implicated in the metabolism of sterols, terpenes, gibberellins, isoflavonoids, and xenobiotics. Evidence that cytochromes P-450 are involved in the detoxification of herbicides (chlorotoluron, primsulfuron, and diclofop) includes photoreversible CO inhibition of the reactions, and a requirement for 02 and NADPH. Several cytochromes P-450, Mr 45,000 to 65,000, have been isolated, including hydroxylases of cinnamic acid, 3,9-dihydroxypterocarpan, and digitoxin. In some cases the purified cytochrome P-450 has been successfully reconstituted with NADPH:cytochrome P-450 reductase (Mr 72,000-84,000 protein). This reductase appears to be a nonspecific electron donor to different forms of cytochrome P-450. Immunological techniques and specific inhibitors (triazoles, imidazole derivatives) are being used to characterize plant cytochromes P-450 and the NADPH:cytochrome P-450 reductase. Specific cytochromes P-450 are induced by wounding or pathogens, others are expressed in specific cell types. Plant cytochromes P-450 are found in various subcellular locations, including endoplasmic reticulum, plasma membranes, glyoxysomes, and perhaps mitochondria. A cytochrome P-450 demethylase from avocado has recently been sequenced and found to have a hydrophobic N terminus similar to the membrane anchor of cytochromes P-450 from other organisms. The existence of cytochromes P-450 in different subcellular locations suggests that there are many genes for cytochromes P-450 in plants which have yet to be identified and classified.Cyt P-450 are membrane-bound heme-containing proteins which have been implicated in a variety of oxidative reactions in plant tissues. A wide range of reactions are mediated by specific forms of these proteins. Cyt P-450-linked enzymes have been implicated in biosynthetic pathways leading to the synthesis of lignin phenolics, membrane sterols, phytoalexins, and terpenoids (33). It has been postulated that plants have evolved highly specific Cyt P-450-linked secondary pathways to produce defense-related phytoalexins, while animals have evolved parallel less specific, Cyt P-450-linked systems to detoxify ingested phytoalexins and other xenobiotics (11,22 at the expense of the 450 nm peak (25). For this reason the CO-hemoprotein adduct with the 420 nm peak, termed P-420, is often considered to be a degradation product of Cyt P-450.In addition to the nonspecific inhibition by CO, certain Cyt P-450 activities are selectively inhibited by various imidazole, pyrimidine, and triazole derivatives. Inhibitor binding also can be determined spectrophotometrically by changes in difference spectra. A typical Cyt P-450 spectrum of any mem-669 www.plantphysiol.org on May 10, 2018 -Published by Downloaded from

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Section: Some Plant Cyt P-450 May Be Involved In Modification Of Herbmentioning

confidence: 99%

“…Recently, such evidence has been acquired for at least three important herbicides, chlorotoluron (21), primsulfuron (7), and diclofop (20). Microsomes isolated from etiolated wheat seedlings hydroxylated chlorotoluron and diclofop.…”

Section: Some Plant Cyt P-450 May Be Involved In Modification Of Herbmentioning

confidence: 99%

Multiple Forms of Plant Cytochromes P-450

Donaldson¹,

Luster²

1991

Plant Physiol.

159

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“…This tolerance is due, at least in part, to the high capacity of wheat to detoxify the biocidal metabolite diclofop acid (23). Wheat contains an active MFO which catalyzes the physiologically irreversible aryl-hydroxylation of diclofopacid (15). The aryl-hydroxyl group is glucosylated to form a sugar conjugate with little or no herbicidal activity.…”

mentioning

confidence: 99%

Cross-Resistance to Herbicides in Annual Ryegrass (Lolium rigidum)

Holtum

Matthews²,

Häusler³

et al. 1991

Plant Physiol.

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Annual ryegrass (Lollum rigidum) biotype SLR 31 is resistant to the postemergent graminicide methyl-2-[4-(2,4-dichlorophenoxy)phenoxy]-propanoate (diclofop-methyl). Uptake of [14C](Uphenyl)diclofop-methyl and root/shoot distribution of radioactivity in susceptible and resistant plants were similar. In both biotypes, diclofop-methyl was rapidly demethylated to the biocidal metabolite diclofop acid which, in tum, was metabolized to ester and aryl-O-sugar conjugates. Susceptible plants accumulated 5 to 15% more radioactivity in dicloflop acid than did resistant plants. Resistant plants had a slightly greater capacity to form nonbiocidal sugar conjugates. Despite these differences, resistant plants retained 20% of 14C in the biocidal metabolite diclofop acid 192 hours after treatment, whereas susceptible plants, which were close to death, retained 30% in diclofop acid. The small differences in the pool sizes of the active and inactive metabolites are by themselves unlikely to account for a 30-fold difference in sensitivity to the herbicide at the whole plant level. Similar highpressure liquid chromatography elution patterns of conjugates from both susceptible and resistant biotypes indicated that the mechanisms and the products of catabolism in the biotypes are similar. It is suggested that metabolism of diclofop-methyl by the resistant biotype does not alone explain resistance observed at the whole-plant level. Diclofop acid reduced the electrochemical potential of membranes in etiolated coleoptiles of both biotypes; 50% depolarization required I to 4 Mm diclofop acid. After removal of diclofop acid, membranes from the resistant biotype recovered polarity, whereas membranes from the susceptible biotype did not. Intemal concentrations of diclofop acid 4 h after exposing plants to herbicide were estimated to be 36 to 39 micromolar in a membrane fraction and 16 to 17 micromolar in a soluble fraction. Such concentrations should be sufficient to fully depolarize membranes. It is postulated that differences in the ability of membranes to recover from depolarization are correlated with the resistance response of biotype SLR 31.

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“…The major reactions in wheat are the aromatic ring hydroxylation of the 2,4-dichloro-phenyl moiety of the herbicide, followed by conjugation to form an acidic aryl glycoside. Metabolism of diclofop acid in wheat is catalyzed by cytochrome P450-dependent hydroxylase [7]. In wild oat, a carbohydrate conjugation of the carboxylic group in the diclofop produced a neutral glycosyl ester.…”

Section: Metabolism and Selectivity Of Accase Inhibitor Aryloxyphenoxmentioning

confidence: 99%

Herbicide Metabolism in Weeds — Selectivity and Herbicide Resistance

Jablonkai¹

2015

Herbicides, Physiology of Action, and Safety

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The metabolic detoxication/bioactivation pathways, the levels and activity of enzymes, and endogenous cofactors mediating these reactions in crops have been well documented; however, much less evidence has been accumulated in weed species. The herbicide metabolism as a selectivity factor is summarized with special attention to acetyl-CoA carboxylases (ACCase)-inhibiting aryloxyphenoxypropionate, protoporphyrinogen IX oxidase (PPO) inhibitor, carotenoid biosynthesis inhibitor clomazone, and acetolactate synthase (ALS) inhibitor imidazolinone and sulfonylurea herbicides in various weed species. The metabolism-based herbicide resistance related to these herbicide classes is also discussed along with the role and level of metabolizing enzymes and cofactors in weed species.

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Aryl hydroxylation of diclofop by a cytochrome P450 dependent monooxygenase from wheat

Cited by 78 publications

References 23 publications

Multiple Forms of Plant Cytochromes P-450

Multiple Forms of Plant Cytochromes P-450

Cross-Resistance to Herbicides in Annual Ryegrass (Lolium rigidum)

Herbicide Metabolism in Weeds — Selectivity and Herbicide Resistance

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