Transport Of Glyphosate Research Articles

Surfactant-Increased Glyphosate Uptake into Plasma Membrane Vesicles Isolated from Common Lambsquarters Leaves.

Plasma membrane vesicles were isolated from mature leaves of lambsquarters (Chenopodium album L.) to investigate whether this membrane is a barrier to glyphosate uptake and whether surfactants possess differential abilities to enhance glyphosate permeability. Amino acids representing several structural classes showed [delta]pH-dependent transport, indicating that the proteins necessary for active, proton-coupled amino acid transport were present and functional. Glyphosate uptake was very low compared to the acidic amino acid glutamate, indicating that glyphosate is not utilizing an endogenous amino acid carrier to enter the leaf cells and that the plasma membrane appears to be a significant barrier to cellular uptake. In addition, glyphosate flux was much lower than that measured for either bentazon or atrazine, both lipid-permeable herbicides that diffuse through the bilayer. Glyphosate uptake was stimulated by 0.01% (v:v) MON 0818, the cationic surfactant used in the commercial formulation of this herbicide for foliar application. This concentration of surfactant did not disrupt the integrity of the plasma membrane vesicles, as evidenced by the stability of imposed pH gradients and active amino acid transport. Nonionic surfactants that disrupt the cuticle but that do not promote glyphosate toxicity in the field also increased glyphosate transport into the membrane vesicles. Thus, no correlation was observed between whole plant toxicity and surfactant-aided uptake. Current data suggest that surfactant efficacy may be the result of charged surfactants' ability to diffuse away from the cuticle into the subtending apoplastic space, where they act directly on the plasma membrane to increase glyphosate uptake.

Carrier‐mediated uptake of glyphosate in broad bean (Vicia faba) via a phosphate transporter

The possibility that the herbicide glyphosate (N‐phosphonomethylglycine) may be taken up in plant cells via a phosphate transporter of the plasma membrane was investigated using protoplasts of broad bean leaves (Vicia fabaL.). Phosphonoformic acid, a powerful inhibitor of phosphate transport in animal cells, was first demonstrated to be a competitive inhibitor of phosphate uptake inbroad bean protoplasts. Glyphosate was able to inhibit phosphate uptake into the protoplasts, and to protect partially the phosphate transporter from inhibition by phosphonoformic acid. Concentration dependence studies showed that glyphosate uptake exhibited a saturable phase at low glyphosate concentrations (0. 5 to 3 μM), superimposed by a linear uptake at higher concentrations (up to 100 μM). Inhibition of glyphosate uptake by para‐chloromercuribenzene sulphonic acid, sodium azide and carbonyl‐cyanide‐m‐chlorophenylhydrazone was much stronger at 1 than at 100 μM glyphosate. Kinetics indicated that the saturable component of glyphosate transport was competitively inhibited by either phosphate or phosphonoformic acid. It is concluded that glyphosate can be absorbed via a phosphate transporter of the plasma membrane

Penetration and effects of glyphosate in isolated potato mitochondria

The penetration and effects of the sodium salt of glyphosate, N-(phosphonomethyl) glycine, in isolated potato tuber mitochondria were investigated. The penetration studyrequired the measurement of the volume of mitochondrial water space and this measurement was repeatedlycarried out using [ 14C]dextran giving a value of 3.53 μl mg −1 protein. After a 15 minute incubation periodwith medium containing 1 μM or 1 mM glyphosate, without respiratory substrate, almost no product was found in themembrane pellet, after disruption of the organelles in distilled water. In contrast, glyphosate was found in themitochondrial water in a range of concentrations close to the external medium concentration. These results show that, at leastthe diffusion equilibrium between the medium, the intermembrane space and the matrix area was readily reached forglyphosate. The greater part of the product penetrated during the first five minutes of the incubation period.The glyphosate content, in mitochondria operating at 25°, was not changed by adding either substrate. (state IV), orsubstrate + ADP (state III). The probability of an active glyphosate transport by the mitochondrial inner membrane wastherefore very unlikely. Glyphosate, at a concentration as high as 50 mM, was unable to change therespiratory activities of isolated potato tuber mitochondria(oxygen consumption rate with different substrates, ADP/O, respiratorycontrol values, etc.).

Glyphosate Transport and Early Effects on Shikimate Metabolism and Its Compartmentation in Sink Leaves of Tomato and Spinach Plants

Glyphosate (N[phosphonomethyl]glycine) applied to an assimilate-exporting leaf of tomato or spinach plants is translocated via the phloem to the young growing areas of the shoot apex and root where it causes the rapid accumulation of shikimate and shikimate 3-phosphate to up to 16% of the dry weight or these tissues. Using the technique of non-aqueous fractionation of spinach leaves it was shown that the herbicidal target of glyphosate, the shikimate pathway enzyme 5-enolpyruvlyshikimate 3-phosphate synthase, is located within the chloroplast and that, in the presence of glyphosate. shikimate 3-phosphate accumulates in the same organelle, while shikimate was preferentially localized in the vacuolc. The major part of [l4C]glyphosatc imported into the leaf via the phloem was detected in the cytosolic fraction of the mesophyll cells.

Apoplastic and Symplastic Pathways of Atrazine and Glyphosate Transport in Shoots of Seedling Sunflower

[(14)C]Atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino]-s-triazine) and [(14)C]glyphosate (N-[phosphonomethyl]glycine) were xylem fed to sunflower shoots at 100 micromolar for 1 hour in the light, then placed in the dark at 100% relative humidity for 1, 4, 7, or 10 hours. The distribution of atrazine and glyphosate between shoot parts, in the leaves, and between the aoplast and symplast of the leaf was determined. The apoplastic concentrations and distribution patterns of atrazine and glyphosate in the leaves were evaluated using a pressure dehydration technique, our results were compared to the previously reported distribution patterns of the naturally occurring apoplastic leaf solutes, and the apoplastic dye PTS (trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate). The pattern of atrazine and glyphosate distribution in the shoot, and between the leaf apoplast and symplast, was found to reflect the potential of these herbicides to enter the shoot symplast. The results of this study are discussed with respect to current theories of xenobiotic transport in plants, and have been found to be consistent with the intermediate permeability hypothesis for xenobiotic transport.

Effect of Leaf Girdling and Rhizome Girdling on Glyphosate Transport in Quackgrass (Agropyron repens)

Glyphosate transport was studied using the14C-labeled herbicide. Because glyphosate appears to undergo little metabolism in plants, detected14C was assumed to indicate the presence of glyphosate. Leaf-girdling experiments demonstrated that14C-glyphosate [N-(phosphonomethyl)glycine] transport in treated quackgrass [Agropyron repens(L.) Beauv. ♯3AGRRE] leaves occurred in both leaf symplast and apoplast. Symplastic transport was toward the leaf tip and the leaf base. Apoplastic transport was toward the leaf tip only. Rhizome-girdling experiments showed that translocation of glyphosate from a treated shoot to another shoot on the same rhizome occurs primarily in the rhizome symplast. Girdling the base of quackgrass culms showed that acropetal transport of glyphosate from the rhizome into quackgrass shoots is in the apoplast and the symplast of the culms of quackgrass shoots. Excision of rhizome buds and rhizome apices indicated that the rhizome is a sink for glyphosate independent of rhizome buds or rhizome apices. The concentration of14C-glyphosate in rhizome buds was less in plants with rhizome apices removed than in those with apices intact. The concentration of C-glyphosate in rhizome apices did not differ between plants with buds removed and those with buds intact.14C-glyphosate applied to a girdled rhizome apex remained primarily in the apex. Some transport of glyphosate past the girdle occurred, indicating apoplastic transport of glyphosate in the rhizome. Apoplastic transport of14C-glyphosate in the rhizome was greatest in water-stressed plants.

Carbon Partitioning and Herbicide Transport in Glyphosate-Treated Sugarbeet (Beta vulgaris)

Glyphosate [N-(phosphonomethyl)glycine] had several effects on carbon translocation in sugarbeet (Beta vulgarisL. ‘Klein E multigerm’): a) import of carbon by sink leaves was inhibited, b) net starch accumulation in source leaves was stopped, and c) carbon export from source leaves in the dark was stopped following 10 h of treatment in the light. During periods when no carbon was exported, glyphosate also was not transported from treated leaves. The limitation of glyphosate transport, resulting from disruption of carbon metabolism, appears important in the study and use of the herbicide.

A Watershed Study of Glyphosate Transport in Runoff

AbstractGlyphosate (N‐[phosphonomethyl]glycine)3 formulated as Round‐up® herbicide,4 was applied on 0.3‐ to 3.1‐ha watersheds at rates of 1.10‐, 3.36‐, and 8.96‐kg/ha as a preseeding herbicide in the no‐tillage establishment of rescue (Festuca arundinacea L.) and corn (Zea mays L.). Runoff from natural rainfall following early springtime treatments was measured and analyzed to define concentration and transport of glyphosate under these conditions.The highest concentration of glyphosate (5.2 mg/liter) was found in runoff occurring 1 day after treatment at the highest rate. Glyphosate (2 µg/liter) was detected in runoff from this watershed up to 4 months after treatment. For the lower application rates, maximum concentration of the herbicide in runoff was < 100 µg/liter for events occurring 9–10 days after application and decreased to <2 µg/liter within 2 months of treatment. The maximum amount of glyphosate transport by runoff was 1.85% of the amount applied, most of which occurred during a single storm on the day after application. In each of the three study years, herbicide transport in the first runoff event following treatment accounted for 99% of the total runoff transport on one watershed. Glyphosate residues in the upper 2.5 cm of treated soil decreased logarithmically with the logarithm of time; they persisted several weeks longer than in the runoff water.

EFFECTS OF GROWTH STAGE ON TRANSLOCATION OF GLYPHOSATE IN QUACK GRASS

Visual symptoms of toxicity (inhibition of leaf growth and bud germination) were used to study the influence of growth stage of quack grass (Agropyron repens (L.) Beauv.) on glyphosate (N-phosphonomethyl glycine) transport and efficiency. Glyphosate (or a toxic metabolite) moved in sufficient quantity from the point of application on the leaf within 1 day to significantly affect the regrowth and within 2 days to affect the regenerative potential of rhizomes. As quack grass plants developed to the four-leaf stage the effect of glyphosate treatment increased. When only one shoot was sprayed on a rhizome supporting two shoots at the same leaf stage, glyphosate inhibited leaf growth on the untreated shoot at the two-leaf stage but not at the four-leaf stage. Similarly, glyphosate inhibited leaf growth on tillers when only the main shoot was sprayed. However, when only the tiller was sprayed, leaf production was not affected on the main shoot suggesting that glyphosate is phloem mobile.