Evidence Against a Direct Membrane Effect in the Mechanism of Action of Graminicides

Weed Science ◽  
1994 ◽  
Vol 42 (2) ◽  
pp. 302-309 ◽  
Author(s):  
Joseph M. Di Tomaso
Keyword(s):  
Specific Interaction ◽  
Herbicide Tolerance ◽  
External Solution ◽  
Protonated Form ◽  
Weak Acid ◽  
Antagonistic Interaction ◽  
Phytotoxic Activity ◽  
Broadleaf Species ◽  
Rigid Ryegrass ◽  
Acid Herbicides

The aryloxyphenoxypropionate and cyclohexanedione herbicides, which inhibit acetyl-coenzyme A carboxylase (EC 6.4.1.2), have also been hypothesized to act at specific sites on the plasmalemma. An impermeant sulfhydryl binding agent was reported to block the diclofop acid-induced depolarization of the membrane potential (Em) in rigid ryegrass. A correlation between the antagonistic interaction with auxin herbicides both in the field and in the Emresponse, and the repolarization of Emin herbicide-resistant rigid ryegrass following removal of diclofop acid also provide support for this hypothesis. However, similar membrane responses in resistant grasses and broadleaf species suggest that the membrane response may not be important in the phytotoxic activity of the postemergence graminicides under field conditions. In addition, an antagonistic interaction was not observed in roots of susceptible grasses exposed to combinations of diclofop-methyl and 2,4-D. Furthermore, the repolarization of the Emin diclofop-resistant rigid ryegrass was correlated to differential acidification of the external solution and an increase in the protonated form of diclofop acid, rather than a site-specific interaction at the plasmalemma. Although the membrane response is probably not involved in herbicide phytotoxicity in agricultural systems, a higher extracellular pH in the resistant biotypes of rigid ryegrass may inhibit the movement of these weak-acid herbicides across the plasmalemma, and possibly contribute to increased herbicide tolerance.

Soil pH Interference in the Behavior of Weak Acid Herbicides

2021 ◽  
pp. 43-64
Author(s):  
Levi Andres Bonilla Rave ◽  
Kassio Ferreira Mendes ◽  
Daniela Margarita Echeverri Delgadillo ◽  
Dilma Francisca de Paula ◽  
Adalin Cezar Moraes de Aguiar ◽  
...  
Keyword(s):  
Soil Ph ◽  
Weak Acid ◽  
Acid Herbicides

Weed control by 2,4-D dimethylamine depends on mixture water hardness and adjuvant inclusion but not spray solution storage time

2020 ◽  
Vol 34 (1) ◽  
pp. 107-116 ◽  
Author(s):  
Geoffrey P. Schortgen ◽  
Aaron J. Patton
Keyword(s):  
Weed Control ◽  
Storage Time ◽  
Water Hardness ◽  
Hard Water ◽  
Quality Parameters ◽  
Weak Acid ◽  
Hardness Level ◽  
Spray Solution ◽  
Water Conditioning ◽  
Acid Herbicides

AbstractHerbicides are an important tool in managing weeds in turf and agricultural production. One of the earliest selective herbicides, 2,4-D, is a weak acid herbicide used to control broadleaf weeds. Water-quality parameters, such as pH and hardness, influence the efficacy of weak acid herbicides. Greenhouse experiments were conducted to evaluate how varying water hardness level, spray solution storage time, and adjuvant inclusion affected broadleaf weed control by 2,4-D dimethylamine. The first experiment evaluated a range of water-hardness levels (from 0 to 600 mg calcium carbonate [CaCO3] L−1) on efficacy of 2,4-D dimethylamine applied at 1.60 kg ae ha−1 for dandelion and horseweed control. A second experiment evaluated dandelion control from spray solutions prepared 0, 1, 4, 24, and 72 h before application. Dandelion and horseweed control by 2,4-D dimethylamine was reduced when the CaCO3 level in water was at least 422 or at least 390 mg L−1, respectively. Hard-water antagonism was overcome by the addition of 20 g L−1 ammonium sulfate (AMS) into the mixture. When AMS was included in spray mixtures, no differences were observed at 600 mg CaCO3 L−1, compared with distilled water. Spray solution storage time did not influence dandelion control, regardless of water-hardness level or adjuvant inclusion. To prevent antagonism, applicators should use a water-conditioning agent such as AMS when applying 2,4-D dimethylamine in hard water.

Confocal ratio-imaging of intercellular pH in unfertilised mouse oocytes

Zygote ◽  
1994 ◽  
Vol 2 (1) ◽  
pp. 37-45 ◽  
Author(s):  
C.R. House
Keyword(s):  
Confocal Microscopy ◽  
Uniform Distribution ◽  
Laser Light ◽  
External Solution ◽  
Calibration Procedure ◽  
Weak Acid ◽  
Scanning Confocal Microscopy ◽  
Mouse Oocytes ◽  
Weak Bases ◽  
Ratio Imaging

SummaryUnfertilised mouse oocytes absorbed the pH-sensitive fluoroprobe SNARF-1-AM (carboxyseminaphthorhodafluor-1-acetoxymethylester), the ester being hydrolysed by an intracellular esterase. Ratioimaging of oocytes containing the resultant SNARF-1 excited by laser light (514nm) has been obtained by scanning confocal microscopy with appropriate barrier filters to monitor emission maxima about 590 and 640 nm recorded simultaneously in separate channels of the framestore. Images produced by pixel-by-pixel division of these channel images showed uniform distribution of SNARF-1 in equatorial regions in most cells. However, in some oocytes regions (about 4 μm diameter) with smaller ratios (i.e. lower pHi) were detected. The relation between the ratio of emitted maxima and the extracellular pH (pHo) in the presence of nigericin allowed a calibration procedure to determine the intracellular pH (pHi). With this mehod pHi was estimated to be 7.13±0.05 (mean ± SEM, n = 31). Whereas the application of a weak acid (butyric) caused a fall in the ratio and hence in pHi, exposure to weak bases (NH4Cl or trimethylamine) caused a rise. Large changes in pH0. did not evoke corresponding changes in the ratio and hence in pHi. Addition of 5% CO2 to the external solution buffered at the usual value of pH 7.4, however, did cause a fall in the ratio which was reversible only when HCO3− was present in the external solution.

scholarly journals The Hexose-Proton Cotransport System of Chlorella

1974 ◽  
Vol 64 (5) ◽  
pp. 568-581 ◽  
Author(s):  
Ewald Komor ◽  
Widmar Tanner
Keyword(s):  
Sugar Transport ◽  
Protonated Form ◽  
Weak Acid ◽  
Sugar Uptake ◽  
Sugar Accumulation ◽  
Maximal Velocity ◽  
Uptake System ◽  
High Affinity ◽  
Ph Values ◽  
Proton Concentration

The proton concentration in the medium affects the maximal velocity of sugar uptake with a Km of 0.3 mM (high affinity uptake). By decreasing the proton concentration a decrease in high affinity sugar uptake is observed, in parallel the activity of a low affinity uptake system (Km of 50 mM) rises. Both systems add up to 100%. The existence of the carrier in two conformational states (protonated and unprotonated) has been proposed therefore, the protonated form with high affinity to 6-deoxyglucose, the unprotonated form with low affinity. A plot of extrapolated Vmax values at low substrate concentration versus proton concentration results in a Km for protons of 0.14 µM, i.e. half-maximal protonation of the carrier is achieved at pH 6.85. The stoichiometry of protons cotransported per 6-deoxyglucose is close to 1 at pH 6.0–6.5. At higher pH values the stoichiometry continuously decreases; at pH 8.0 only one proton is cotransported per four molecules of sugar. Whereas the translocation of the protonated carrier is strictly dependent on sugar this coupling is less strict for the unprotonated form. Therefore at alkaline pH a considerable net efflux of accumulated sugar can occur. The dependence of sugar accumulation on pH has been measured. The decrease in accumulation with higher pH values can quantitatively be explained by the decrease in the amount of protonated carrier. The properties of the unprotonated carrier resemble strikingly the properties of carrier at the inner side of the membrane. The inside pH of Chlorella was measured with the weak acid 5,5-dimethyl-2, 4-oxazolidinedion (DMO). At an outside pH of 6.5 the internal pH was found to be 7.2. To explain the extent of sugar accumulation it has to be assumed that the membrane potential also contributes to active sugar transport in this alga.

scholarly journals Effect of Carbonaceous Soil Amendments on Potential Mobility of Weak Acid Herbicides in Soil

2012 ◽  
pp. 497-500
Author(s):  
William C. Koskinen ◽  
Alegria Cabrera ◽  
Kurt A. Spokas ◽  
Lucia Cox ◽  
Jennifer L. Rittenhouse ◽  
...  
Keyword(s):  
Soil Amendments ◽  
Weak Acid ◽  
Acid Herbicides ◽  
Potential Mobility

scholarly journals Lower formulation pH does not enhance bentazone uptake into plant foliage

2002 ◽  
Vol 55 ◽  
pp. 163-167 ◽  
Author(s):  
Z.Q. Liu
Keyword(s):  
Plant Cells ◽  
Sinapis Alba ◽  
Weak Acid ◽  
Foliar Uptake ◽  
Plant Foliage ◽  
Wheat Leaves ◽  
Spray Formulation ◽  
Acid Herbicides

Lower pH generally favours the diffusion of weak acid compounds in vitro into plant cells Such a rule may not be applicable to the uptake of formulated weak acid herbicides applied to plant foliage in vivo In this study the effect of spray formulation pH (5 7 and 9) on the foliar uptake of a weak acid herbicide bentazone which is used as a formulated salt was investigated using three plant species mustard (Sinapis alba) wheat (Triticum aestivum) and bean (Vicia faba) Greater uptake of the herbicide occurred at pH 9 and pH 7 than at pH 5 on mustard and wheat leaves Uptake of bentazone into bean was slow (< 20 after 24 h) regardless of carrier pH However in the presence of a surfactant faster uptake was achieved with higher pH The results are discussed in relation to the lipophilicity and the solubility of weak acid chemicals as influenced by pH

Mechanisms of Herbicide Absorption Across Plant Membranes and Accumulation in Plant Cells

Weed Science ◽  
1994 ◽  
Vol 42 (2) ◽  
pp. 263-276 ◽  
Author(s):  
Tracy M. Sterling
Keyword(s):  
Plant Cell ◽  
Cell Membranes ◽  
Plant Cells ◽  
Physicochemical Characteristics ◽  
Weak Acid ◽  
Ion Trapping ◽  
Metabolic Inhibitors ◽  
Plant Cell Membranes ◽  
Plant Membranes ◽  
Acid Herbicides

In most cases, a herbicide must traverse the cell wall, the plasma membrane, and organellar membranes of a plant cell to reach its site of action where accumulation causes phytotoxicity. The physicochemical characteristics of the herbicide molecule including lipophilicity and acidity, the plant cell membranes, and the electrochemical potential in the plant cell control herbicide absorption and accumulation. Most herbicides move across plant membranes via nonfacilitated diffusion because the membrane's lipid bilayer is permeable to neutral, lipophilic xenobiotics. Passive absorption of lipophilic, ionic herbicides or weak acids can be mediated by an ion-trapping mechanism where the less lipophilic, anionic form accumulates in alkaline compartments of the plant cell. A model that includes the pH and electrical gradients across plant cell membranes better predicts accumulation concentrations in plant cells of weak acid herbicides compared to a model that uses pH only. Herbicides also may accumulate in plant cells by conversion to nonphytotoxic metabolites, binding to cellular constituents, or partitioning into lipids. Evidence exists for herbicide transport across cell membranes via carrier-mediated processes where herbicide accumulation is energy dependent; absorption is saturable and slowed by metabolic inhibitors and compounds of similar structure.

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