Browsing by Author "Zama, Paul"

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    Studies on the mechanisms of action of the herbicide safener CGA- 92194
    Zama, Paul (Virginia Polytechnic Institute and State University, 1985)
    CGAr92194 {α-[1,3-dioxolan-2-yl-methoxy)imino]benzeneacetonitrile} is a herbicide safener that is used as a seed dressing agent (1.25 g ai/kg seeds) to protect grain sorghum [Sorghum bicolor (L.) Moench] against metolachlor [2-chloroi-N-(2-ethyl-6-methylphenyl-N-(2-methoxy1-methylethyl)acetamide] injury. The potential adverse phytotoxic effects and the mechanisms of the protective action of this safener were studied in laboratory experiments. Adverse phytotoxicity was assessed by comparing CGA-92194 and the herbicide safeners cyometrinil {(Z)-α[(cyanomethoxy)imino]benzeneacetonitrile} and flurazole [phenylmethyl 2-chloro-4-(trifluromethyl)-5-thiazolecarboxylate] for their effects on CO₂ fixation, protein, DNA, RNA and lipid syntheses of enzymatically isolated leaf cells of soybean [Clycine max (L.) Merr]. At physiological concentrations of less than 10 μM, CGA-92194, cyometrinil and flurazole were stimulatory of all metabolic processes. At 100 μM, the safeners were inhibitory of the five processes with flurazole being the most potent. The mechanisms of the safening action of CGA-92194 were studied by examining the potential interactions of this safener with metolachlor at the levels of uptake and macromolecular syntheses in enzymatically isolated leaf mesophyll protoplasts of grain sorghum. The influence of CGA-92194 on the in vitro reactivity of metolachlor with glutathione (GSH) and it metabolism by sorghum seedlings were also examined. When CGA-92194 and metolachlor were given simultaneously, CGA-92194 enhanced the uptake of ¹⁴C-metolachlor into the sorghum protoplasts in a concentration-dependent pattern. Thus, interference with herbicide uptake is not involved in the protective action of this safener Treatments with metolachlor and CGA-92194 in combination inhibited the incorporation of ¹⁴C-uracil, ³H-thymidine and ¹⁴C-acetate into sorghum protoplast macromolecules less than metolachlor given alone, suggesting the potential involvement of a competitive antagonism in the mechanism of action of CGA-92194. The metabolic activity and growth of sorghum seedlings grown from CGA-92194-pretreated seeds was significantly lower than that of seedlings grown from untreated seeds at 10 or 20 days after planting, The relationship of these effects of CGA-92194 to its safening action is unclear at the present time. CGA-92194 increased the in vitro chemica1 reactivity of metolachlor for GSH in a concentration-dependent pattern, Sorghum seedlings grown from safener-pretreated seeds enhanced ¹⁴C-metolachlor absorption and stimulated its metabolism via conjugation to GSH. This stimulation was reduced by tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethy1)- oxirane] a potent inhibitor of plant GSH-S-transference enzymes, These results indicate that a safener-induced stimulation of the spontaneous or enzymatic conjugation of metolachlor with GSH is most likely involved in the protective action of CGA-92194. It is suggested that the safening mechanism of action of CGA—92194 involves a sequence of multilevel interactions which together contribute to the overall protection of grain sorghum from metolachlor injury.