Christian Gauvrit

Mechanisms of Resistance to Glyphosate in a Ryegrass (Lolium multiflorum) Biotype from Chile

Abstract Glyphosate behavior was examined in Italian ryegrass plants from Chile that were sensitive (S) and resistant (R) to this herbicide. In order to explain the resistance to glyphosate, contact angles, spray retention, foliar uptake, herbicide translocation, and target enzyme activity were studied. Contact angles of glyphosate solutions at a field concentration were 40° to 45° on the abaxial surface of R leaves as compared to 70° on S. Glyphosate spray retention by R plants was 35% lower than by S plants. Glyphosate uptake by the abaxial leaf surface of R plants was about 40% lower than that of S plants. In addition, in the R plants more glyphosate migrated to the tip of the treated leaves. The target enzyme in R and S plants was sensitive to the herbicide. Based on these and previous results, it is concluded that resistance in this Italian ryegrass biotype results from lower spray retention, lower foliar uptake from the abaxial leaf surface, and altered translocation pattern. The decreases in spray retention and foliar uptake constitute new mechanisms of glyphosate resistance. Nomenclature: Glyphosate; Italian ryegrass; Lolium multiflorum Lam. LOLMU

Glyphosate response to calcium, ethoxylated amine surfactant, and ammonium sulfate

Calcium ion in the spray water can reduce glyphosate efficacy. Ammonium sulfate (AMS) is commonly added to the spray tank to overcome the reduced efficacy. However, it is sometimes claimed that ethoxylated tallow amine surfactant (EA) is also efficacious, provided that calcium concentration is moderate (= 5 mM, 200 ppm). On response curves of ‘Plaisant’ barley treated with glyphosate, the presence of calcium ion increased the glyphosate dose needed to obtain 50% (ED50) barley growth reduction. The addition of AMS to the spray tank overcame the antagonistic effect of the calcium ion and restored glyphosate efficacy. EA was less effective than AMS at 5 or 10 mM calcium ion concentration as measured by ED50. However, at 90% growth reduction (ED90), EA was more effective than AMS at the 5 mM calcium ion concentration but less effective at the 10 mM concentration. Hence, at a moderate (= 5 mM) calcium concentration, EA would be an effective adjuvant. Calcium ion decreased the foliar uptake of glyphosate but did not affect the rate of uptake. AMS but not EA restored foliar uptake to values observed without calcium ion. EA increased spray retention, and this probably accounted for the increased glyphosate efficacy at low calcium concentration. Nomenclature: Glyphosate; barley, Hordeum vulgare L. Additional index words: Ammonium sulfate, bioassay, dose–response curve, ethoxylated tallow amine, foliar uptake, spray retention. Abbreviations: AMS, ammonium sulfate; EA, ethoxylated tallow amine; SE, standard error.

Uptake and fate of triticonazole applied as seed treatment to spring wheat (Triticum aestivum L.)

Following seed treatment of wheat (Triticum aestivum L.) with 14C-labelled triticonazole at a dose of 1·8 g kg-1 seed, the uptake of radioactivity by shoots and roots was investigated from the two- to three-leaf stage up to the beginning of the booting phase, 80 days after sowing. Triticonazole equivalents taken up by wheat plants reached 5·7% and 14·6% of the applied dose in the shoots and the roots, respectively. Between the two- to three-leaf stage and the beginning of the booting phase, the concentration of triticonazole equivalents in the shoots decreased from 2·5 to 0·15 μg g-1 fresh weight. This was attributed to uptake of triticonazole by roots not keeping pace with shoot growth and increased retention in the roots of triticonazole taken up. The main factor limiting the uptake of triticonazole by the roots may be the rapid growth of the uptake-active apical root parts out of the dressing zone which had formed in the soil. Distribution of triticonazole equivalents taken up by the main shoot showed a decreasing concentration gradient from the oldest to the youngest leaf. An increase in the seed treatment dose was investigated as a way to increase the concentration of triticonazole in the shoots, but its influence remained limited.

Action of methomyl analogues on maize mitochondria

Abstract Methomyl analogues were assayed on mitochondria isolated from male sterile (T cytoplasm) and male fertile maize. None of them was more selective than Methomyl. The analogues which were more efficient than Methomyl displayed no selectivity. The results suggest stringent steric requirements for Methomyl action and stress the importance of the electron conjugated system in the Methomyl molecule for its efficiency.

Uptake of Triticonazole, during Imbibition, by Wheat Caryopses after Seed Treatment

The uptake of 14C-labelled triticonazole by wheat caryopses during imbibition was investigated. The uptake from an aqueous solution appeared to be driven by mass flow rather than by accumulation in seed lipids. During treatment with a liquid seed-dressing preparation of triticonazole, c. 1 μg triticonazole per caryopsis (2·4% of applied triticonazole) entered the seed. During germination in soil, another c. 1 μg triticonazole per caryopsis entered the seed in 24 h. In killed seeds, no penetration was observed between 24 h and 72 h after the beginning of imbibition. After seed treatment and imbibition in soil, triticonazole appeared to be located in the seed coats and embryo, but not in endosperm; experiments suggested that the testa acted as a barrier. Under our conditions, the pathway from seed coats to shoots was not an important route for triticonazole uptake by the shoots.

Biological activity of the two geometrical isomers of methomyl on maize mitochondria

Abstract Methomyl ( S -methyl- N [(methylcarbamoyl)oxy]thioacetimidate), the active ingredient in lannate insecticide, gave a geometrical isomer after acid

Methomyl analogues with increased biological activity towards F7T maize mitochondria

Abstract Methomyl analogues were synthesized by substituting alkyl moieties (C 2 -C 21 ) in the place of the carbamic methyl. They were assayed on mitochondria isolated from male sterile (F 7 T) and male fertile (F 7 N) maize. They had no action on F 7 N mitochondria. The heptadecyl (C 17 ) and heneicosanyl (C 21 ) derivatives had no conspicuous effect on F 7 T mitochondria. By contrast, the ethyl, propyl, butyl, nonyl, tridecyl (C 13 ) and pentadecyl (C 15 ) derivatives had the same type of activity as Methomyl on F 7 T mitochondria, namely stimulation of NADH oxidation and inhibition of malate oxidation. Moreover, the concentration at which they were maximally effective decreased from 10 mM (Methomyl) to 3 μM (tridecyl derivative); hence, the latter compound has a biological activity which is nearly the same as that of Helminthosporium maydis toxin.

Effects of the herbicides benzoylpropethyl and flampropisopropyl on rat liver mitochondria: An alteration in membrane fluidity?

Abstract The action of the herbicides benzoylpropethyl and flampropisopropyl, and the corresponding unesterified acids was studied in rat liver mitochondria. The herbicides were found to (a) inhibit the mitochondrial electron transfer in complex III or at the level of ubiquinone (I50 of 4 nmol mg protein−1 for flampropisopropyl and 18 for benzoylpropethyl with succinate as a substrate); (b) have an additional (however less sensitive) site of inhibition near succinate dehydrogenase; and (c) interfere with energy transfer. Sensitivity was increased 2- (benzoylpropethyl) and 3.5-fold (flampropisopropyl) as the rats age increased from 12–13 weeks to 23–26 weeks. The free acids were far less effective. Since the herbicides benzoylpropethyl and flampropisopropyl are readily hydrolyzed by animals and since the free acids are less effective than the herbicides, it explains why these potentially harmful compounds have a low acute toxicity. Swelling studies in isoosmotic salts suggested that the two herbicides decrease membrane fluidity, an action which was assumed to be responsible for the electron transfer inhibition and, via inhibition of phosphate transport, the interference with energy transfer.

The experimental herbicide UKJ72J is an inhibitor of succinate oxidation in plant mitochondria

not received UKJ72J Herbicide Thiopyrimidine Plant mitochondria Inhibitor Succinate oxidation

Inhibition of succinate oxidation by the herbicide UKJ72J

Abstract The inhibitory activity of the herbicide UKJ72J on succinate oxidation in mitochondria from various plant species was studied. In monocotyledons (Gramineae: wheat, oat, maize; Liliaceae: onion, leek) succinate oxidation was affected only at high concentrations. Among dicotyledons widely differing sensitivities were found: in Solanaceae (tomato, potato, tobacco), Leguminosae (mung bean, soybean) and Compositae (sunflower) I 50 concentrations for UKJ72J inhibition were below 55 μM. In Cruciferae (turnip, cauliflowers Chenopodiaceae (lambsquarter, beetroot) and Compositae (endive) I 50 were between 100 and 250 μM, whereas in Rosaceae (apple, pear) and Umbelliferae (carrot, fennel) I 50 were near (apple) or higher than 500 μM. No correlation could be found between the sensitivity to UKJ72J of mitochondrial succinate oxidation in these families and their location in the presently accepted flowering plant classification.