The response of resistant and susceptible plants to diclofop‐methyl

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Electrophysiological measurements were made on the mesophyll cells of wheat (Triticum aesti'um L. cv Waldron) and oat (APena satiia L. cv Garry) coleoptiles treated either with the herbicide didofop-methyl (methyl 2-(4-(2',4'-dichlorophenoxy)phenoxy)propanoate), or it's primary metabolite diclofop, (2-(4-(2',4'-dichlorophenoxy)phenoxy)-propanoic acid). Application of a 100 micromolar solution of diclofopmethyl to wheat coleoptiles had little or no effect on the membrane potential (EM) however in oat, EM slowly depolarized to the diffusion potential (ED). At pH 5.7, 100 micromolar diclofop rapidly abolished the electrogenic component of the membrane potential in both oat and wheat coleoptiles with half-times of 5 to 10 minutes and 15 to 20 minutes, respectively. The concentrations giving half-maximal depolarizations in wheat were 20 to 30 micromolar compared to 10 to 20 micromolar in oat.The depolarizing response was not due to a general increase in membrane permeability as judged from the EM'S response to changes in K+, Na', Cl-, and S042-, before and after treatment with diclofop and from its response to KCN treatment. In both plants, diclofop increased the membrane permeability to protons, makin the EM strongly dependent upon the external pH in the range of pH 5.5 to pH 8.5. The effects of diclofop can best be explained by its action as a specific proton ionophore that shuttles protons across the plasmalemma. The rapidity of the cell's response to both diclofop-methyl (15-20 minutes) and diclofop (2-5 minutes) makes the ionophoric activity a likely candidate for the earliest herbicidal event exhibited by these compounds.Diclofop-methyl (methyl 2-(4-(2',4'-dichlorophenoxy)phenoxy)propanoate) is a selective postemergence grass herbicide that controls wild oat and other grasses in wheat (1). The reasons for its phytotoxicity and selectivity are not known for certain. The selectivity is probably due to a differential metabolism between susceptible and tolerant species (8). In both susceptible oats and resistant wheat, diclofop-methyl is rapidly hydrolized to the free acid, diclofop (24442',4'-dichlorophenoxy)phenoxy)propanoic acid. In wheat diclofop is subsequently metabolized by aryl hydroxylation and conjugation to form an acidic, aryl-glucoside; in oat, diclofop is metabolized to a neutral glucosyl ester (7,14,21,23 ofdiclofop-methyl is less well understood than is the metabolism. In susceptible plants such as oat, diclofop-methyl induced an inhibition of leaf, stem, and root elongation, chlorosis of leaves (11), and severe damage to cellular ultrastructure (2). After 92 h treated leaves contained chloroplasts with compressed grana thylakoids and indistinct envelopes while the remainder of the cytoplasm had extensive vesiculation similar to that seen in senescent cells (2). Simultaneous application of diclofop-methyl and auxic herbicides such as 2,4-D under field conditions resulted in a reduction in herbicidal activity of both diclofop-methyl and the auxic compound (6). Shimabukuro et al. (22) have rep...

mentioning

confidence: 98%

Effects of Diclofop and Diclofop-Methyl on the Membrane Potentials of Wheat and Oat Coleoptiles

Wright¹,

Shimabukuro²

1987

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“…Similar observations are now being reported for plants. In plants both the aryloxyphenoxypropionate diclofop (11,19,25) and the cyclohexanedione sethoxydim (24) reduced electrochemical potentials across plant cell membranes. Diclofop, applied as the free acid, depolarized membrane potentials in Chara cells (13).…”

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confidence: 99%

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

Häusler¹,

Holtum²,

Powles³

1991

The herbicidally active aryloxyphenoxypropionates diclofop acid, haloxyfop acid, and fluazifop acid and the cyclohexanedione sethoxydim depolarized membranes in coleoptiles of eight biotypes of herbicide-susceptible and herbicide-resistant annual ryegrass (Lo/ium rigidum). Membrane polarity was reduced from -100 millivolts to -30 to -50 millivolts. Membranes repolarized after removal of the compounds only in biotypes with resistance to the compound added. Repolarization was not observed in herbicide-susceptible L. rigidum, nor was it observed in biotypes resistant to triazine, triazole, triazinone, phenylurea, or sulfonylurea herbicides but not resistant to aryloxyphenoxypropionates and cyclohexanediones. Chlorsulfuron, a sulfonylurea herbicide, at a saturating concentration of 1 micromolar, reduced membrane polarity in all biotypes studied by only 15 millivolts. The recovery of membrane potential following the removal of chlorsulfuron was restricted to chlorsulfuron-susceptible and -resistant biotypes that did not exhibit diclofop resistance. These differences in membrane responses are correlated with resistance to dicloflop rather than with resistance to chlorsulfuron. It is suggested that the differences may reflect altered membrane properties of diclofop-resistant biotypes. Further circumstantial evidence for dissimilarity of properties of membranes from diclofop-resistant and diclofop-susceptible ryegrass is provided by observations that K+/Na+ ratios were significantly higher in coleoptiles from diclofop-resistant biotypes than in coleoptiles from susceptible plants. Intact and excised roots from susceptible biotypes were capable of acidifying the external medium, whereas roots from resistant biotypes were unable to do so. The ineluctable conclusion is that in L. rigidum the phenomena of membrane repolarization and resistance to aryloxyphenoxypropionate and cyclohexanedione herbicides are correlated.

“…However, none of the above mechanisms appears to be significantly involved in the antagonism between DM and 2,4-D (7,8). In intact plants the sensitive sites of action appear to be the meristematic zones (3,8,9,15). The (20,21).…”

mentioning

confidence: 99%

Reciprocal Antagonism between the Herbicides, Diclofop-Methyl and 2,4-D, in Corn and Soybean Tissue Culture

Shimabukuro¹,

Walsh²,

Hoerauf³

1986

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The antagonistic interaction between the grass herbicide, diclofopmethyl (methyl 2-14(2',4'-dichlorophenoxy)phenoxylpropanoate) (DM), and 2,4-dichlorophenoxyacetic acid (2,4-D), was demonstrated in DMresistant soybean (Glycine max [L.] Meff.) and DM-susceptible corn (Zea mays L.). 2,4-D caused root shortening and thickening, and induced callus growth in soybean and corn root tissue cultures at 1 and 10 micromolar. Normal soybean root growth was unaffected by 10 micromolar DM whereas corn root growth was inhibited completely by 1 to 10 micromolar DM. DM at 10 micromolar reversed completely the induction of callus growth by 1 micromolar 2,4-D in soybean roots. In cor, 10 micromolar 2,4-D reversed the growth inhibiting activity of 1 micromolar DM and induced callus growth. The antagonistic interaction between DM and 2,4-D was reciprocal and the activity of either compound depended upon the relative concentration of the other. 2,4-D did not antagonize or decrease the activity of DM by decreasing its uptake by root tissues or increasing the rate of its detoxication. The antagonistic interaction between DM and 2,4-D probably involves cellular activity associated with actively growing and proliferating cells and reqnires the presence of both compounds at the sensitive site.Diclofop-methyl (DM),' is a selective postemergence herbicide that controls wild oat (Avenafatua L.) and other annual grasses in wheat (Triticum aestivum L.) (1). DM acts like a proton ionophore to dissipate rapidly the cell membrane potential in oat (Avena sativa L.) (24) and Chara cells (14). DM inhibits IAA-induced coleoptile growth and acidification (19,20) and probably causes a loss of apical dominance in wild oat root tips (3). Lipid metabolism is affected strongly in sensitive species (10) and severe ultrastructural cell membrane damage occurs with time (2). DM is poorly translocated from both leaves (2) and roots (13).The auxinic herbicide, 2,4-D, is used to control broad-leaved weeds in wheat. Therefore, a single application of DM and 2,4-D should control both wild oat and broad-leaved weeds in wheat. However Corn and soybean seeds were disinfected by rinsing in sterile distilled H20 containing detergent, transferred to 1% NaOCl (v/v) for 5 min, and rinsed twice in sterile distilled H20. Corn seeds were soaked for an additional hour in 0.15% (v/v) NaOCl following the 1% (v/v)