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Using extracts from suspension-cultured cells of soybean (Glycine max cv. Mandarin) as a source of active enzymes, the activities of glutathione transferases (GSTs) catalysing the conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) and selective herbicides were determined to be in the order CDNB fomesafen > metolachlor = acifluorfen > chlorimuron-ethyl. GST activities showed a thiol dependence in a substrate-specific manner. Thus, GST activities toward acifluorfen and fomesafen were greater when homoglutathione (hGSH), the endogenously occurring thiol in soybean, was used as the co-substrate rather than glutathione (GSH). Compared with GSH, hGSH addition either reduced or had no effect on GST activities toward other substrates. In the absence of enzyme, the rates of hGSH conjugation with acifluorfen, chlorimuron-ethyl and fomesafen were negligible, suggesting that rapid hGSH conjugation in soybean must be catalysed by GSTs. GST activities were subsequently determined in 14-day-old plants of soybean and a number of annual grass and broadleaf weeds. GST activities of the plants were then related to observed sensitivities to post-emergence applications of the four herbicides. When enzyme activity was expressed on a mg -1 protein basis, all grass weeds and Abutilon theophrasti contained considerably higher GST activity toward CDNB than soybean. With fomesafen as the substrate, GST activities were determined to be in the order soybean Echinochloa crus-galli > Digitaria sanguinalis > Sorghum halepense = Setaria faberi with none of the broadleaf weeds showing any activity. This order related well to the observed selectivity of fomesafen, with the exception of A. theophrasti, which was partially tolerant to the herbicide. Using metolachlor as the substrate the order of the GST activities was soybean > A. theophrasti S. halepense > Amaranthus retroflexus > Ipomoea hederacea, with the remaining species showing no activity. GST activities toward metolachlor correlated well with the selectivity of the herbicide toward the broadleaf weeds but not toward the grass weeds. Acifluorfen and chlorimuron-ethyl were selectively active on these species, but GST activities toward these herbicides could not be detected in crude extracts from whole plants.

Polyclonal and monoclonal antibodies reactive with acifluorfen (AF) were prepared by the immunization of, respectively, rabbits and mice with AF-bovine serum albumin conjugates. The reactivities of polyclonal antibody and three monoclonal antibodies (AF 9-1, AF 51-5 and AF 75-144) were examined in an indirect competitive enzyme-linked immunosorbent assay (C-ELISA). The polyclonal antibody reacted with AF at concentrations of 1.5 to 800 μg litre -1 , while the monoclonal antibodies reacted with AF at concentrations of 3 to 24 μg litre -1 for AF 9-1, 1.5 to 12 μg litre -1 for AF 51-5 and 12 to 48 μg litre -1 for AF 75-144. In the presence of up to 40% methanol in C-ELISA, the monoclonal antibodies, particularly AF 75-144, were less affected in their reactivities with AF than was the polyclonal antibody. Moreover AF 9-1 and AF 51-5 specifically reacted with acifluorfen-methyl and oxyfluorfen, while AF 75-144 reacted with chlornitrofen which did not react with the other antibodies. These results indicated that the antibodies are useful for the assay of AF and its related compounds.

Protoporphyrinogen oxidase (Protox) was inhibited stereoselectively by three pairs of enantiomers belonging to diphenyl ether (DPE) and pyrazole phenyl ether (PPE) herbicide classes. The (R) enantiomers were 10- to 44-fold more active than the (S) enantiomers as inhibitors of Protox from barley etioplasts. Similarly, the (R) enantiomers caused green barley tissue to accumulate greater amounts of porphyrins and caused greater tissue damage than the (S) enantiomers. The (R) enantiomers competed more successfully with [ 14 C]acifluorfen than the (S) enantiomers for the binding sites on Protox. In the PPE class, the in-vitro and in-vivo activity differences were wider in the isopropyl pairs than in the n-propyl pairs. The DPE enantiomers were tested on ten dicotyledonous and six monocotyledonous weed species and ten crops for weed control and crop safety. In general, neither enantiomer had pre-emergence activity on monocotyledons, but the (R) enantiomer provided some monocotyledonous weed control when applied post-emergence. On dicotyledons, the (R) enantiomer provided excellent pre-emergence control, whereas the (S) enantiomer was inactive. The (R) enantiomer caused no injury to corn, cotton, peanuts, rice, sorghum, or soybeans applied pre-emergence, but it severely injured crops when applied post-emergence. There was a positive correlation between the activities of the compounds at the molecular, cellular and whole plant levels. The only molecular property differences found to account for differences in activity between members of chiral pairs were steric parameters.

«Sylgard® 309» organosilicone surfactant is a very effective adjuvant for broadleaf weed control with a number of herbicides. It is also effective in providing rainfastness to these post-emergence herbicide applications. To elucidate the basis for herbicide activity enhancement and rainfastness, the absorption of [ 14 C]acifluorfen, [ 14 C]bentazone and [ 14 C]«Sylgard 309» were studied. Non-ionic surfactants and crop oil concentrates were used as adjuvants with [ 14 C]acifluorfen and [ 14 C]bentazone, respectively, for purposes of comparison (.)

The photolysis of acifluorfen, sodium 5-[2-chloro-4-(trifluoromethyl)-phenoxy]-2-nitrobenzoate (I) in aqueous solution afforded only 2-chloro-1-(4-nitrophenoxy)-4-trifluoromethylbenzene (II) arising from photodecarboxylation. The reaction followed first-order kinetics, though the photo-reaction rate was solvent-dependent. A mechanism that accounts for the formation of the product is proposed.

The biological activity of the sodium salt of acifluorfen was determined for velvetleaf (Abutilon theophrasti), cocklebur (Xanthium pensylvanicum), morning-glory (Ipomoea sp.), and soybean (Glycine max) in greenhouse tests and by a leaf-disc efflux assay which bypasses cuticular penetration. The greenhouse activity in order of decreasing control was morning-glory > cocklebur > velvetleaf > soybean. Activity in the efflux assay in order of decreasing control was velvetleaf ≈ morning-glory > cocklebur > soybean. Leaf wetting was determined by contact angle measurements. Cocklebur wets very readily, and this was attributed partly to its more polar wax content. Soybean wets very poorly, primarily due to its large leaf hairs, which accounts for part of acifluorfen selectivity. Surfactants and inorganic salts increased penetration in a species-specific manner, and as penetration increased, so did activity. Acifluorfen-sodium is more active on velvetleaf than on cocklebur in a leaf-disc efflux assay, but in the greenhouse the reverse is true. This may be explained by the fact that penetration is eight times greater in cocklebur than in velvetleaf. The chemical composition of the leaf waxes was determined for each species by gas chromatography–mass spectroscopy (GC/MS). Morning-glory and velvetleaf waxes consist mainly of long-chain esters. Soybean wax is primarily a C-30 alcohol. Cocklebur wax is primarily composed of one material which is not a typical leaf wax. This component could not be conclusively identified, but contains several carbonyls, several vinyl groups, and possibly a hydroxyl group. This wax is more polar than the other leaf waxes and seems to account for the extremely good wetting and high degree of penetration in cocklebur compared to the other species. Wax composition does not relate to penetration or activity in the other three species tested. More complex differences in cuticle structure and biological sensitivity probably account for differences in penetration and activity.

The effect of acifluorfen and oxyfluorfen on chlorophyll bleaching, lipid peroxidation and photosynthesis in pea leaf discs was studied. Both her- bicides induced light-dependent bleaching and lipid peroxidation, the level of damage being greater at higher light intensities. Photosynthetic carbon dioxide fixation was only partially inhibited in treated leaf discs incubated in darkness, thus indicating that these herbicides did not inhibit photo- synthesis as a primary mode of action. Leaf discs maintained in darkness showed no visible signs of injury, and light-dependent herbicide-induced damage was reduced by incubating discs under nitrogen, orpre-incubating them with the electron-transport inhibitor monuron. It is suggested that acifluorfen and oxyfluorfen are activated by a light-dependent process, which requires photosynthetic electron transport.