Influence of Herbicide Safeners on Herbicide Metabolism

Gronwald, John W.

doi:10.1016/b978-0-12-332910-3.50008-4

Cited by 24 publications

(17 citation statements)

References 86 publications

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“…On the other hand, NA appeared to enhance the GST activity of wheat seedlings, in contrast to another report (Edwards and Cole 1996). NA thus induced the same type of effect in wheat as in maize and sorghum (Gronwald 1989). In addition, the protein content of shoots increased (Table 1).…”

Section: Isolation Of the Total Complement Of Gstscontrasting

confidence: 72%

Purification and characterization of a safener‐induced glutathione S‐transferase from wheat (Triticum aestivum)

Pascal¹,

Scalla²

1999

Physiologia Plantarum

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The genome of cultivated wheat is hexaploid, and in consequence a large number of glutathione S‐transferase (GSTs, EC 2.5.1.18) isozymes is expected in that organism. Wheat GST subunits were first analyzed by reverse‐phase high performance liquid chromatography (RP‐HPLC). In root and shoot tissues, subunits 4, 8, and 9 were constitutively expressed whereas subunits 2, 3, and 5 were inducible by the herbicide safener naphthalic anhydride (NA). Significant differences were observed, however, between the distributions of these six major subunits in roots and shoots. A major GST isozyme was purified from the shoots of plants treated by NA. A combination of ammonium sulphate precipitation, hydrophobic interaction chromatography (HIC) and affinity chromatography resulted in purification with an apparent yield of 4.6% and a 48‐fold increase in specific activity toward 1‐chloro‐2,4‐dinitrobenzene (CDNB). Analysis by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) showed a single band at 24.5 kDa. Molecular mass estimated by nondenaturing PAGE was 49.5 kDa. These results suggest that the enzyme exists as a dimer. A pI of 5.2 was determined by native isoelectric focusing (IEF). Analysis by 2‐D electrophoresis showed a single spot, with a pI of 5.8–5.9. However, further analysis by RP‐HPLC revealed that the two subunits were different. They were characterized and identified by electrospray ionization mass spectrometry (ESI‐MS) as subunits 2 and 3, molecular masses 24 924±3 and 24 958±5 Da, respectively. Therefore, GST(2–3) is apparently a heterodimer consisting of subunits 2 and 3. Apparent KM values were 424 μM for CDNB and 228 μM for glutathione (GSH). GST(2–3) metabolized the herbicide fluorodifen, and a KM of 22 μM was determined for the herbicide.

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Section: Isolation Of the Total Complement Of Gstscontrasting

confidence: 72%

Purification and characterization of a safener‐induced glutathione S‐transferase from wheat (Triticum aestivum)

Pascal¹,

Scalla²

1999

Physiologia Plantarum

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“…Applied to seeds either prior to planting or directly to the soil together with the herbicide, safeners reduce the phytotoxicity of the herbicide through at least one of the following three mechanisms: (1) decreased uptake or translocation of the herbicide, (2) competitive binding with the herbicide at the active site of the cognate enzyme(s), and (3) increased herbicide metabolism (Hatzios 1983). Although exceptions have been reported, the majority of research in this area suggests that enhancement of herbicide metabolic activity is the predominant mechanism of safener action (reviewed in Gronwald 1989;Hatzios 1991).…”

Section: Regulation Of Plant P450 Expression By Herbicides and Herbicmentioning

confidence: 97%

Plant cytochrome P450-mediated herbicide metabolism

2006

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In the last two decades it has become apparent that enzymes of the P450 monooxygenase (P450) superfamily are responsible for the Phase I metabolism of numerous herbicides representing several classes of organic compounds. The majority of experimental evidence for P450 involvement in herbicide metabolism has been derived from in vitro studies in which the catalytic activity of plant microsomes towards herbicidal substrates was measured in the presence of various P450 inhibitors and activators. While the studies with microsomes elicited much appreciation for the pivotal roles of plant P450s in herbicide metabolism, detailed characterization of these enzymes only became possible after the isolation of genes encoding specific isoforms responsible for herbicide conversion. Several lines of evidence suggest that the development of herbicide resistance in weeds by enhanced detoxification is frequently associated with elevated levels of P450 activity. Enhanced detoxification-based herbicide resistance is particularly difficult to control, because it can involve resistance to multiple, chemically unrelated classes of herbicides. Continued research efforts are aimed at elucidating the role of P450s in the metabolic fates of herbicides in plants and the development of herbicide resistance in weeds. Recent advances made in the isolation and genetic manipulation of P450 enzymes have created new opportunities for their application in engineering herbicide tolerance and bioremediation.

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“…However, it is surprising that GST-M activity continued to increase at 10 and 100 pM benoxacor, because these concentrations did not provide protection any greater than did 1 p~ benoxacor (Table I). If we assume that safening activity is due primarily to induction of GST activity, as indicated in studies of the mode of action of benoxacor (Kreuz et al, 1989;Viger et al, 1991b) and other safeners (Gronwald et al, 1987;Gronwald, 1989;Fuerst and Lamoureux, 1992), there is a need to explain why further increases in GST-M titer did not lead to greater protection. Two explanations are suggested: (a) The inhibition of growth that was seen even at very high benoxacor concentrations was the result of inhibition of growth by metolachlor during germination or emergence, before maximal induction of GST-M by benoxacor; altematively, (b) at such high metolachlor concentrations, further increases in GST-M titer did not completely prevent metolachlor from reaching shoot meristematic regions.…”

Section: Effect Of Benoxacor Concentration In Growth Medium On Growthmentioning

confidence: 99%

Partial Characterization of Glutathione S-Transferase Isozymes Induced by the Herbicide Safener Benoxacor in Maize

1993

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The effects of the dichloroacetamide safener benoxacor on maize (Zea mays 1. var Pioneer 3906) growth and glutathione Stransferase (CST) activity were evaluated, and CST isozymes induced by benoxacor were partially separated, characterized, and identified. Protedion from metolachlor injury was closely correlated with CST activity, which was assayed with metolachlor as a substrate, as benoxacor concentration increased from 0.01 to 1 p~. CST adivity continued to increase at higher benoxacor concentrations (10 and 100 PM), but no further protection was observed.Total CST activity with metolachlor as a substrate increased 2.6-to 3.8-fold in response to 1 p~ benoxacor treatment. Total CST activity from maize treated with or without 1 p~ benoxacor was resolved by fast protein liquid chromatography anion-exchange chromatography into four major activities, designated adivity peaks A, B, C, and D in their order of elution. These CST activity peaks were enhanced to varying degrees by benoxacor. Activity peak B showed the least induction, whereas activity peak A was absent constitutively and thus highly induced by benoxacor. In contrast to earlier reports, there appear to be not one, but at least two, major constitutive isozymes (adivity peaks A and D) having activity with metolachlor as substrate; there were at least three such isozymes in benoxacor-treated maize (activity peaks A, C, and D). l h e elution volumes of activity peaks A, B, C, and D were compared with those of partially purified maize CST I and CST 11; also, the reactivity of polypeptides in these activity peaks with antisera to CST I or CST 1/111 (mixture) was evaluated. Evidence from these experiments indicated that adivity peak B contained CST I, and adivity peak C contained CST II and CST 111. Adivity peaks A and D contained unique CSTs that may play a major role in metolachlor metabolism and in the safening activity of benoxacor in maize. lsozymes present in adivity peaks A and D were not detected in earlier reports because of the very low activity with the artificial substrate l-chloro-2,4-dinitrobenzene. Immunoblotting experiments also indicated the presence of numerous unidentified CST subunits, including multiple subunits in chromatography fractions containing single peaks of CST adivity; this is indicative of the likely complexity and diversity of the maize CST enzyme family.GST enzymes catalyze the conjugation of GSH to electrophilic, lipophilic molecules. The GSH conjugates formed are

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Influence of Herbicide Safeners on Herbicide Metabolism

Cited by 24 publications

References 86 publications

Purification and characterization of a safener‐induced glutathione S‐transferase from wheat (Triticum aestivum)

Purification and characterization of a safener‐induced glutathione S‐transferase from wheat (Triticum aestivum)

Plant cytochrome P450-mediated herbicide metabolism

Partial Characterization of Glutathione S-Transferase Isozymes Induced by the Herbicide Safener Benoxacor in Maize

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