Aryldiones incorporating a [1,4,5]oxadiazepane ring. Part 2: chemistry and biology of the cereal herbicide pinoxaden

BACKGROUND: Pinoxaden is a new cereal herbicide that provides outstanding levels of post‐emergence activity against a broad spectrum of grass weed species for worldwide selective use in both wheat and barley. RESULTS: Factors influencing activity and tolerance to pinoxaden were in part linked to distinct structural parts of the active ingredient. Three complementary contributions that decisively impact upon the herbicidal potency against grasses were identified: a preferred 2,6‐diethyl‐4‐methyl aromatic substitution pattern, a dione area suitable for proherbicide formation and beneficial adjuvant effects. The uptake and translocation pattern of pinoxaden when coapplied with its tailored adjuvant were analysed by autoradiography, indicating extensive and rapid penetration, followed by effective distribution throughout the plant. Crop injury reduction on incorporation of the [1,4,5]oxadiazepane ring into the aryldione template was reinforced with safener technology. Comparative studies on the behaviour of pinoxaden applied either alone or in combination with the safener cloquintocet‐mexyl demonstrated that addition of the safener resulted in significant enhancement of metabolic degradation in wheat and barley, providing excellent crop tolerance and a substantial selectivity margin without adverse effects on weed control. CONCLUSION: The biological potential of pinoxaden and its active principle pinoxaden dione in terms of grass weed control and tolerance in cereals was fully exploited by inclusion of the safener cloquintocet‐mexyl in the formulation in combination with a specific and tailor‐made tank‐mix adjuvant based on methylated rape seed oil. Copyright © 2011 Society of Chemical Industry     

Uptake and phytotoxicity of chlorsulfuron in Zea mays L. in the presence of 1,8-naphthalic anhydride

The sites of uptake of chlorsulfuron in maize (Zea mays L.) were investigated at three different growth stages. Exposure of seedling roots, or shoots separately, to herbicide-treated sand over 4 days resulted in inhibition of both roots and shoots. Exposure of seedling roots to chlorsulfuron-treated soil over 21 days severely inhibited both roots and foliage, while separate shoot exposure also reduced both foliage and root growth. After plant emergence, exposure of the crown root node, growing point and lower stem to treated soil reduced foliage and root growth, but exposure of the shoot above the growing point caused only slight inhibition of foliage and had no effect on roots. The herbicide safener 1,8-naphthalic anhydride (NA) applied as a dust (10 g kg^?1 seed weight), or as a 50 mg 1^?1 suspension in water to maize seeds, reduced the root inhibition by chlorsulfuron in 4-day-old seedlings. NA completely prevented both foliage and root injury when chlorsulfuron was placed in soil in the shoot zone before emergence, or in the shoot zone below the soil surface after plant emergence. NA slightly decreased injury to foliage, but not to roots when chlorsulfuron was placed in soil in the root zone before emergence. NA seed treatment protected both roots and foliage against injury from foliarly applied chlorsulfuron. Plants were also protected when a suspension of NA in water was sprayed on the foliage seven days before chlorsulfuron. When a mixture of NA and chlorsulfuron was applied to foliage, root injury was reduced more than foliage injury.     

The foliar uptake of isoproturon by wheat and Alopecurus myosuroides huds

The uptake and translocation of ¹⁴C-isoproturon (3-p-cumenyl-1-1,-dimethylurea) in wheat (tolerant) and backgrass (sensitive) following foliar treatment under controlled environmental conditions were examined. The amount of ¹⁴C-isoproturon translocated through the xylem was about 10 times that translocated through the phloem in both wheat and blackgrass. However, 25.5% of the applied ¹⁴C-isoproturon was translocated in the xylem in blackgrass, compared with 8.9% in wheat. ¹⁴C-isoproturon did not respond significantly to induced sink-demand in either species. Leaf-disc autoradiograms revealed the absorption of ¹⁴C-isoproturon by the minor veins and translocation into the cut vein endings. No significant differences were found in between wheat and blackgrass in this respect.     

Studies on the selectivity of alloxydim-sodium in plants

Alloxydim-sodium, methyl 3-[1-(allyloxyimino)butyl]-4-hydroxy-6,6-dimethyl-2-oxocyclohex-3-enecarboxylate sodium salt, is a selective herbicide which controls grass weeds in a wide range of broad-leaf crops. Spray retention, tested at two growth stages, was generally greater for the broad-leaf crops (cotton, sugarbeet, flax, beans and peas) than for wild oat (Avena fatua L.), blackgrass (Alopecurus myosuroides Huds), barley and couch grass [Agropyron repens (L.) Beauv.], and did not contribute to selectivity between susceptible and tolerant species. Broad-leaf crops tolerated 2820 g alloxydim-sodium ha^?1, three times the recommended rate used to control annual grasses. Differential uptake and translocation were not factors contributing to selectivity. In wild oat, blackgrass and sugarbeet, uptake and translocation of ¹⁴C continued during a period of 14 days after treatment with [¹⁴C]alloxydim-sodium. Translocation in susceptible and tolerant species was predominately symplastic. Over 40% of the applied ¹⁴C was eliminated from treated wild oat, blackgrass and sugarbeet plants within 7 days, due to degradation and volatilisation. A greater proportion of the methanol-soluble radioactivity extracted from leaves and roots was present as water-soluble polar metabolites in sugarbeet, than in wild oats, 7 days after treatment. The proportion of unaltered alloxydim in the organo-soluble fraction of a methanol extract was greater in wild oat than in sugarbeet. Differential metabolism appears to be one of the factors contributing to alloxydim-sodium selectivity between sugarbeet and wild oat.     

Effect of benzoylprop-ethyl on uptake, transport and metabolism of 32P in Avena fatua L. and Triticum aestivum L.

The effect of benzoylprop-ethyl on plant weight, root uptake, transport and metabolism of ³²P in wild oat and wheat plants was examined 4 h, 1,3 and 9 days after treatment. The fresh weight of wild oat plants was significantly reduced, due to herbicide action only, by day 9 after treatment. By day 3, shoot weight was decreased while root weight was significantly increased by 47%. No significant changes in plant weight were caused by benzoylprop-ethyl in wheat plants. Uptake of ³²P by treated wild oat plants decreased by 39% compared with the control, by day 9, after an initial increase; uptake of ³²P was not significantly influenced in wheat plants. By day 1 transport of ³²P to the shoots was significantly reduced in wild oat plants by 34%, whereas in wheat plants it was significantly increased by 35%. Metabolism of ³²P was already hampered in wild oat plants 4 h after treatment. The content of ³²P was reduced on the first two sampling dates in both the roots and shoots of treated plants in all fractions except in DNA in the shoots. On day 3, this decrease was apparent especially in organic, lipidic and nucleic acid fractions in the shoots; incorporation of ³²P into lipidic and RNA fractions was significantly inhibited on day 9 in both the roots and shoots of treated wild oat plants. Wheat plants responded most strongly to benzyoylprop-ethyl on day 1 after treatment, when ³²P incorporation into all fractions except DNA was hampered. Differences between treated and control wheat plants gradually levelled off on days 3 and 9 after treatment.     

Uptake, translocation and metabolism of the herbicide florasulam in wheat and broadleaf weeds

Florasulam is a triazolopyrimidine sulfonanilide post-emergence broadleaf herbicide for use in wheat (Triticum aestivum L.). The selectivity of florasulam to wheat has been determined to be related primarily to a differential rate of metabolism between wheat with a half-life of 2.4 h and broadleaf weeds with half-lives ranging from 19 to >48 h. To a lesser extent, selectivity, at least for the broadleaf weed cleavers (Galium aparine L.), involves uptake differences. Rate of metabolism data were generated using greenhouse-grown plants injected with radiolabelled florasulam and subsequent extraction and processing by high-performance liquid chromatography (HPLC). Structures of metabolites were determined by isolation for nuclear magnetic resonance and liquid chromatography/mass spectrometry. Wheat plants metabolised florasulam by hydroxylation of the aniline ring para to the nitrogen, followed by conjugation to glucose. Metabolism by broadleaf weeds was so slow that isolation of metabolite was not possible, but comparison of HPLC data suggested hydroxylation as the major pathway.     

Comparative uptake and metabolism of methazole in prickly sida and cotton

The comparative uptake and metabolism of ¹⁴C-labeled 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (methazole), a herbicide, in prickly sida (Sida spinosa L.) and cotton (Gossypium hirsutum L.) were investigated as physiological bases for herbicidal selectivity, using thin layer chromatography, autoradiography, and liquid scintillation counting. Prickly sida and cotton readily absorbed and translocated ¹⁴C from nutrient solution containing [¹⁴C]methazole. Only acropetal translocation of ¹⁴C was observed. Methazole was rapidly metabolized to 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) and other metabolites by both species. Although metabolism appeared to be qualitatively the same, quantitative differences between species were evident. Methazole was converted to DCPMU (also phytotoxic) more readily by prickly sida than cotton; however, DCPMU was more readily detoxified to 1-(3,4-dichlorophenyl) urea (DCPU) by cotton than prickly sida. More ¹⁴C per unit weight was present in the prickly sida shoots than in cotton shoots. Also, a larger portion of the methanol-extractable ¹⁴C was herbicidal in the shoots of prickly sida than of cotton. Thus, the differential tolerances of prickly sida and cotton to methazole may be explained, in part, by differential uptake and metabolism of methazole and DCPMU.     

Root absorption and translocation of 5-substituted analogs of the imidazolinone herbicide,imazapyr

In preparation for assessing quantitative structure-activity relationships (QSAR) for root absorption and translocation of imidazolinones herbicides, 13 radiolabeled analogs of imazapyr (2-(4-isopropyl–4-methy1–5-oxo-2-imidazolin-2-yl) nicotinic acid) substituted in the 5-position of the pyridine ring were evaluated in corn (Zea mays L.) and sunflower (Helianthus annuus L.). The compounds (10 μm) were supplied to the roots through a hydroponic solution for 8 h and, following harvest, plant tissues were either combusted to measure total uptake of radiolabeled material or were extracted for determination of the extent of degradation of the parent compound. Root absorption in both species varied by two orders of magnitude among analogs while translocation, expressed as a percentage of absorption, varied by only three- or four-fold. Few differences were observed for translocation of radioactivity from sunflower stems to leaves. Although six of the analogs were partially metabolized in corn, little metabolism of the imidazolinone analogs occurred in sunflower. These data indicate that meaningful models of root absorption and subsequent translocation to shoots may be developed for 5-substituted analogs of imazapyr, particularly when applied to sunflower.     

The basis of selectivity of 4-(2, 6-dichlorobenzyloxymethyl)-4-ethyl-2, 2-dimethyl-1, 3-dioxolan (WL 29, 226), a new pre-emergence herbicide for use in cereals

A series of pot experiments were undertaken to assess the selectivity of the pre-emergence herbicide 4-(2, 6-dichlorobenzyloxymethyl)-4-ethyl-2, 2, -dimethyl-1, 3-dioxolan (WL 29,226) against a number of annual weeds in wheat. When applied at dose rates of 0.5–2 kg/ha it gave good control of a number of annual monocotyledonous weeds, including Alopecurus myosuroides (blackgrass), without any adverse effects on the crop. WL 29,226 is relatively immobile in soil, remaining at the soil surface and thus favouring uptake via the emerging shoot. Since WL 29,226 is transported predominantly via the xylem, to reach its site of action in the regions of cell division, and hence to be effective, the compound has to penetrate the shoot either at or below the stem apex. The roots are inhibited only when these come into direct contact with the compound. Selectivity of the herbicide is dependent upon the relative anatomical positions of the stem apices of the weeds and the crop with respect to the soil surface. Mesocotyl elongation in many of the weed species was such that the meristematic tissue was raised to the soil surface and into contact with the compound during the emergence of the shoot. In contrast, the stem apex of wheat remained some distance below the soil surface until considerably later, by which time the leaf sheaths offered protection to the meristematic tissue from direct contact with the herbicide. Selectivity is further enhanced in the field as a result of both the depth of planting for wheat and the tendency of many annual weed species to germinate more readily when near the soil surface. Tolerance of the wheat is lost where it germinates in direct contact with the herbicide, due to the lack of any biochemical selectivity. Under field conditions WL 29,226 gives good control of many dicotyledonous species. In pot experiments, however, these exhibit some tolerance to the compound. Radio-tracer studies indicate that the tolerance shown by the shoots of these plants is due to limited transport of the herbicide from the shoot to its site of action at the apex. This suggests that control of broad-leaved weeds occurs predominantly through an inhibition of root growth. However, in species such as sugar-beet, soyabean and cotton a rapid rate of root elongation confers increased tolerance to the compound. Availability of WL 29,226 for uptake by young seedlings is favoured by soil moisture. Low temperatures further improve performance by reducing the rate of shoot emergence and hence prolonging contact with the compound at the most sensitive stage of growth. After emergence uptake of the compound via the shoot becomes a less efficient mode of entry.     

7种苗后除草剂对菵草的除草活性以及对小麦的安全性评价

为了筛选对菵草高效且对小麦安全的除草剂品种,采用温室盆栽法测定了 7种苗后除草剂对菵草的除草活性以及对小麦的安全性.结果表明,5％唑啉草酯EC和15％炔草酯WP对菵草防效优异,ED90仅为各自田间登记低剂量的1/3和1/2;50％异丙隆WP和7.5％啶磺草胺WG对菵草防效较好,ED90与各自田间登记高剂量相当;69 g...     

Absorption, translocation, and fate of propyzamide in witloof chicory (Cichorium intybus L.) and common amaranth (Amaranthus retroflexus L.)

Witloof chicory (Cichorium intybus L.) is tolerant to propyzamide and common amaranth (Amaranthus retroflexus L.) is sensitive. The absorption, translocation, and metabolism of propyzamide was studied in seedlings of witloof chicory and common amaranth to determine if differences in these processes cause the differential sensitivity. At 24,48, and 72 h after root treatment, there was no difference in the concentration of ¹⁴C (g^?1 plant dry wt) in com-mon amaranth and witloof chicory. Approximately 50% of the absorbed ¹⁴C was translocated out of the roots to shoots of both species at 24 and 48 h after treatment. After 72 h about 55 and 74% of the absorbed ¹⁴C was translocated to shoots of witloof chicory and common amaranth, respectively. Distribution of ¹⁴C (g^?1 plant dry wt) in plant parts of witloof chicory and common amaranth seedlings was similar. Roots of both species accumulated the highest concentration of total ¹⁴C, whereas shoots contained the lowest. Thin layer chromatography revealed that the herbicide was metabolized in neither species 48 h after treatment. No differences were found in absorption, translocation, or metabolism between witloof chicory and common amaranth with regard to propyzamide.     

Uptake, translocation and metabolism of aminocyclopyrachlor in prickly lettuce, rush skeletonweed and yellow starthistle

BACKGROUND: Aminocyclopyrachlor is a new herbicide proposed to control broadleaf weeds and shrubs in non‐crop and rangeland systems. To gain a better understanding of observed field efficacy, the uptake and translocation of foliar‐applied aminocyclopyrachlor (DPX‐MAT28) and aminocyclopyrachlor methyl ester (DPX‐KJM44) were evaluated in two annuals, prickly lettuce (Lactuca serriola L.) and yellow starthistle (Centaurea solstitialis L.), and one perennial, rush skeletonweed (Chondrilla juncea L.). RESULTS: Absorption and translocation varied between species. While absorption of DPX‐KJM44 was greater than absorption of DPX‐MAT28, rush skeletonweed absorbed the most, followed by yellow starthistle and prickly lettuce. Overall, the total translocation of either herbicide was highest in yellow starthistle, followed by rush skeletonweed and prickly lettuce. Proportional herbicide movement between species was similar, with the majority translocating to developing shoots. However, in rush skeletonweed, early translocation was directed to root tissue. In rush skeletonweed, no DPX‐MAT28 metabolism occurred, while DPX‐KJM44 was rapidly de‐esterified and translocated as DPX‐MAT28. CONCLUSION: Aminocyclopyrachlor absorption and translocation are dependent on active ingredient structure and species sensitivity. Highly sensitive species such as prickly lettuce absorb and translocate less material than relatively less sensitive species such as rush skeletonweed. De‐esterification of DPX‐KJM44 appears to delay translocation of the resulting acid in yellow starthistle and rush skeletonweed. Copyright © 2011 Society of Chemical Industry     

4种除草剂防除保护性耕作麦田早熟禾效果及其对作物的安全性

通过田间试验,比较4种除草剂药后不同时期对保护性耕作麦田早熟禾的防效及其增产效果,进而比较7．5％啶磺草胺WG、3．6％甲基二磺隆·甲基碘磺隆钠盐WG、15％炔草酸WP、6．9％精唑禾草灵EW 4种除草剂防除早熟禾效果和对小麦的安全性。采用田间药效试验方法,对麦田早熟禾采用喷雾处理,进行4种除草剂防除麦田早熟禾效果及其对作物的安全性试验。7．5％啶磺草胺WG 187．50 g/hm2和3．6％甲基二磺隆·甲基碘磺隆钠盐WG 450．00 g/hm2对早熟禾鲜质量防效分别为83．58％、84．87％。3．6％甲基二磺隆·甲基碘磺隆钠盐WG对春小麦通麦1号品种有一定的药害,药害程度：甲基二磺隆·甲基碘磺隆钠盐＞啶磺草胺。6．9％精唑禾草灵EW、15％炔草酸WP对早熟禾达未到防治要求。187．50 g/hm27．5％啶磺草胺WG,安全性好、防效高、持续期长,可进一步示范推广使用。     

Quantifying the impacts of soil water stress on the winter wheat growth in an arid region, Xinjiang

Wheat growth in response to soil water deficit play an important role in yield stability. A field experiment was conducted for winter wheat (Triticum aestivum L.) during the period of 2002-2005 to evaluate the effects of limited irrigation on winter wheat growth. 80%, 70%, 60%, 50% and 40% of field capacity was applied at different stages of crop growth. Photosynthetic characteristics of winter wheat, such as photosynthesis rate, transpiration rate, stomatal conductance, photosynthetically active radiation, and soil water content, root and shoot dry mass accumulation were measured, and the root water uptake and water balance in different layer were calculated. Based on the theory of unsaturated dynamic, a one-dimensional numerical model was developed to simulate the effect of soil water movement on winter wheat growth using Hydrus-1 D. The soil water content of stratified soil in the experimental plot was calculated under deficit irrigation. The results showed that, in different growing periods, evapotranspiration, grain yield, biomass, root water up- take, water use efficiency, and photosynthetic characteristics depended on the controlled ranges of soil water content. Grain yield response to irrigation varied considerably due to differences in soil moisture contents and irrigation scheduling between seasons. Evapotranspiration was largest in the high soil moisture treatment, and so was the biomass, but this treatment did not produce the highest grain yield and root water uptake was relatively low. Maximum depth of root water uptake is from the upper 80 cm in soil profile in jointing stage and dropped rapidly upper 40 cm after heading stage, and the velocity of root water uptake in latter stage was less than that in middle stage. The effect of limited irrigation treatment on photosynthesis was complex owing to microclimate. But root water uptake increased linearly with harvest yield and improvement in the latter gave better root water uptake under limited irrigation conditions. Appropriately controlled soil wate     

Uptake, translocation and phytotoxicity of root-absorbed haloxyfop in soybean, Festuca rubra L. and Festuca arundinacea Schreb

The concentrations of haloxyfop in nutrient solution required to reduce the total plant dry weight of soybean (Glycine max L. Merr. ‘Evans’), red fescue (Festuca rubra L. ‘Pennlawn’), and tall fescue (Festuca arundinacea Schreb. ‘Houndog’) by 50% (GR₅₀) were determined. The GR₅₀) values for soybean, red fescue and tall fescue were 76 μM, 3μM and 0.4 μM, respectively. The reduction in growth in roots and shoots of soybean was similar. In contrast, the relative reduction in root tissue weight was greater than that for foliar tissue in both grass species. The amount of ¹⁴C-haloxyfop in soybean roots or shoots was higher than in red fescue or tall fescue. Red fescue accumulated less haloxyfop in the foliage than in the roots. On the other hand, similar amounts of ¹⁴C-haloxyfop accumulated in both organs in both soybean and tall fescue. ¹⁴C-haloxyfop appeared to be actively absorbed by the roots of all species. Soybean absorbed more nutrient solution, but utilized it less on a per gram dry matter produced basis than the grass species. Differences in the uptake and translocation of haloxyfop by roots do not account for differences in tolerance between species. However, a higher level of retention of haloxyfop in the roots of red fescue than in tall fescue may provide the former with an additional selectivity advantage under conditions where there is significant root exposure to the herbicide.     

淡紫灰链霉菌株xjy活性产物的抑菌作用及对蔬菜病害的防治效果

拮抗性微生物是生物农药的重要来源之一,加强拮抗菌的应用基础研究对于发展生物农药具有促进作用.在植物病害生物防治中拮抗性微生物主要是链霉菌属及其相关类群[1].     

除草剂安全剂的生理生化作用机制研究进展

除草剂安全剂是一种化学物质,它可以通过生理或生化的途径降低除草剂对作物的毒性,而不降低除草剂的功效.安全剂影响作物的吸收和传导,诱导作物体内P450酶活性、谷胱甘肽调控及其靶标酶ALS的活性.其生理和生化机制研究,不仅有助于安全剂的开发和优化,同时也是了解和运用除草剂活性和抗性机制的途径.该文综述了近年来国内外安全剂生理生化作用机制的研究进展,并探讨其研究方向.     

Selectivity factors relative to asulam for Senecio jacobaea L. control in Medicago sativa L. I. Retention,uptake and translocation*

Senecio jacobaea L. and Medicago sativa L. plants grown in a glasshouse were treated with foliar applications of aqueous solutions of asulam. Retention on foliage, uptake and translocation were measured in both species. Retention was greater in S. jacobaea than in M. sativa when no surfactant was added and similar when surfactant was added. Addition of surfactant modified spray distribution and increased asulam uptake in M. saliva but did not in S. jacobaea. S. jacobaea translocated over twice as much asulam from the treated area as M. sativa. These data suggest that surfactant should not be added for maximum selectivity. Differences in species response to asulam treatments are partially, but not entirely, explained by differences in retention, uptake and translocation.     

Biological activity of pyribenzoxim in winter wheat and associated weeds

Pot and field tests were conducted to evaluate the efficacy of pyribenzoxim for winter weeds in wheat. In the pot tests, pyribenzoxim, at 50 g ha⁻¹, controlled certain biotypes of blackgrass, including a fenoxaprop-P-ethyl-resistant biotype (the "Notts" biotype). A chlorotoluron-resistant blackgrass (the "Peldon" biotype) was not controlled. Cleaver, at the three-to-four-leaf stage, was completely controlled by pyribenzoxim at 30 g ha⁻¹. In the field, the application in December gave good control of common chickweed, but did not control other weeds. No damage to wheat was observed with this rate of pyribenzoxim in December. The application in March gave complete control of blackgrass , hairy chess, and soft brome at 70 g ha⁻¹, and cleaver at 140 g ha⁻¹. The partial control of corn poppy and field violet was achieved. The March application scorched the wheat at 50–70 g ha⁻¹, with prolonged stunting at 100–140 g ha⁻¹. In conclusion, it was shown that pyribenzoxim had potential as a wheat herbicide, but needed further fine-tuning to find an optimum dosage.     

Studies on the mechanism of selectivity of the auxin herbicide quinmerac

Investigations were conducted to elucidate the mechanism of selectivity of the auxin herbicide, quinmerac, in cleavers (Galium aparine) and the tolerant crops sugarbeet (Beta vulgaris), oilseed rape (Brassica napus) and wheat (Triticum aestivum). After root treatment with the herbicide, the selectivity has been quantified as approximately 400-fold between oilseed rape and Galium and 1000-fold between sugarbeet or wheat and the weed species. When 1 and 10 μM [¹⁴C]quinmerac were applied for 4 h, no significant differences between root absorption and translocation of ¹⁴C by Galium and the crop species were found. After 16 h, metabolism of [¹⁴C]quinmerac to the biologically inactive hydroxymethyl and dicarboxylic acid derivatives was more rapid in wheat and sugarbeet than in Galium. In oilseed rape, a lower rate of herbicide metabolism was observed. In Galium, accumulations of abscisic acid (ABA), triggered by quinmerac-stimulated ethylene biosynthesis, were found to cause the herbicidal growth inhibition which develops during 24 h of application. Within 1 h of treatment, quinmerac stimulated 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity and ACC concentration specifically in Galium shoot tissue. During the next 4 h, ACC synthase activity was increased up to 50-fold, relative to the control. Within 3 h of exposure to quinmerac, increased ethylene formation followed by higher ABA levels was detected. In sugarbeet, oilseed rape and wheat, quinmerac did not stimulate ACC synthase activity and ACC and ABA levels. It is suggested that (i) the selectivity of quinmerac is primarily based upon the lower sensitivity to the herbicide of the tissue/target in the crop species, (ii) the induction process of the ACC synthase activity in the shoot tissue is the primary target of herbicidal interference. In wheat and sugarbeet, tolerance to quinmerac is additionally increased by a more rapid metabolism. © 1998 SCI.