Influence of metal salts on the photodegradation of imazapyr, an imidazolinone pesticide

The behaviour of imazapyr (2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid), a broad spectrum herbicide of the imidazolinone family, has been studied under UV radiation in the presence of metal salts. Complexation interactions between imazapyr and metal ions decreased imazapyr photolysis. A chemometric study compared the photodegradation of imazapyr in aqueous solutions in the presence of Na+, Ca2+ or Cu2+ and their concomitant anionic species (Cl-, NO3-) at various pesticide/metal ion molar ratios. The study showed the major role of metal ions in the degradation of imazapyr and its main photoproducts. The molecules were strongly stabilised on complexation with metal ions, leading to an increase in persistence of the pesticide.     

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.     

Dimethoxypyrimidines as Novel Herbicides. Part 2. Synthesis and Herbicidal Activity of O-Pyrimidinylsalicylates and Analogues

A new series of the O-pyrimidinylsalicylates was synthesized and their herbicidal activity was examined. Some of these compounds showed very strong herbicidal activity under pre- and post-emergent treatment conditions against various kinds of grass and broadleaf weeds. Among these compounds, O-(4, 6-dimethoxypyrimidin-2-yl) salicylic acid and its methyl ester were found to exhibit the highest activity. The herbicidal symptoms observed after the treatments included early cessation of plant growth followed by chlorosis, necrosis and plant death. The symptoms were similar to those caused by sulfonylureas and imidazolinones, which inhibit branched-chain amino acid biosynthesis.     

Mechanism of cellular absorption of imidazolinones in soybean (Glycine max) leaf discs

The mechanism of uptake of imazapyr, imazethapyr, and imazaquin into soybean leaf discs was determined. Uptake into the leaf discs was linear with respect to external concentration from 10^?8 to 10^?3 M. Metabolic inhibitors and uncouplers (DNP, FCCP, CCCP, NaN₃, NaCN, DCMU) decreased uptake 58 to 85 %. Uptake was also sensitive to temperature, with maximum uptake occurring at 23°C. The Q₁₀ for uptake between 13 and 23°C was 1-7. The uptake of all 3 imidazolinones was sensitive to the pH of the uptake solution. Maximum uptake occurred at pH 4. However, there were differences in the rate of uptake among the three herbicides. Imazaquin was absorbed the most rapidly followed by imazethapyr and then imazapyr. These differences in uptake reflected the differences in the lipophilicity of the chemicals at pH 4 and 7. The apparent K_ow of imazaquin, imazethapyr and imazapyr at pH 4 was 7-7, 1-4, and 0-1, respectively, and at pH 7 was 0-04, 0-02, and 0-004, respectively. Based on these results the mechanism of uptake is probably best explained by ion trapping.     

Mode of action of naphthalic anhydride as a safener for the herbicide AC 263222 in maize

In hydroponic experiments, seed-dressing with the herbicide safener 1,8-naphthalic anhydride (NA), significantly enhanced the tolerance of maize, (Zea mays L., cv. Monarque) to the imidazolinone herbicide, AC 263222, (2-[4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-5-methylnicotinic acid). Uptake, distribution and metabolism studies where [¹⁴C]AC 263222 was applied through the roots of hydroponically grown maize plants showed that NA treatment reduced the translocation of radiolabel from root to shoot tissue and accelerated the degradation of this herbicide to a hydroxylated metabolite. Reductions in the lipophilicity and, therefore, mobility of this compound following hydroxylation may account for NA-induced retention of radiolabel in the root system. Hydroxylation of AC 263222 suggested that NA may stimulate the activity of enzymes involved in oxidative herbicide metabolism, such as the cytochrome P₄₅₀ mono-oxygenases. In agreement with this theory, the cytochrome P₄₅₀ inhibitor, 1-aminobenzotriazole (ABT), synergized AC 263222 activity and inhibited its hyroxylation in vivo. NA seed-dressing enhanced the total cytochrome P₄₅₀ and b₅ content of microsomes prepared from etiolated maize shoots. Isolated microsomes catalyzed AC 263222 hydroxylation in vitro. This activity possessed the characteristics of a cytochrome P₄₅₀ mono-oxygenase, being NADPH-dependent and susceptible to inhibition by ABT. Activity was stimulated four-fold following NA seed treatment. Differential NA enhancement of AC 263222 hydroxylase and the cytochrome P₄₅₀-dependent cinnamic acid-4-hydroxylase (CA4H) activity, suggested that separate P₄₅₀ isozymes were responsible for each activity. These results indicate that the protective effects of NA result from enhancement of AC 263222 hydroxylation and concomitant reduction in herbicide translocation. This may be attributed to the stimulation of a microsomal cytochrome P₄₅₀ system. © 1998 SCI.     

Mode of action of herbicidal ALS-inhibitors on acetolactate synthase from green plant cell cultures,yeast, and Escherichia coli

Inhibitors of branched-chain amino acid biosynthesis—by inhibiting acetolactate synthase (ALS)—represent the most active group of herbicidal compounds to date (Shaner, D.L., Recent Adv. Phytochem. 23 (1989) 227–61). A microbial screening technique has been developed to investigate known and possible new ALS-inhibitors. Escherichia coli mutant FD 1062, which expresses only valine-resistant ALS II isoenzyme as the solely branched-chain amino acid synthesizing isoenzyme, has been used extensively to optimize known and to screen for new chemical classes of ALS-inhibitors, respectively. Herbicidal compounds like sulfonylureas, triazolopyrimidines, pyrimidylsalicylates, carbamoylpyrazolines, sulfonylimino-azinyl-heteroazoles, sulfonylamide azines, and substituted sulfonyldiamides, respectively, are active on minimal medium with K_i-values which resemble the rank order of biological activity of these compounds in the greenhouse. Interestingly, herbicidal imidazolinones are not at all inhibitory on E.coli strain FD 1062 in vivo although, of course, they exert high activity on isolated bacterial ALS. Similarly, N-protected valylanilides, pyrimidyl mandelic acids, benzenesulfonyl carboxamides, and uhiquinone-O are inactive in the bacterial assay but have been shown by other methods to act as ALS inhibitors. Additionally, reversal experiments can he performed to exclude, e.g. artificial inhibitory effects of test compounds. Moreover, a thin-layer biogram application technique opens the opportunity to test mixtures of chemicals. From green plant cell cultures (Catharanthus roseus) ALS has been isolated and characterized in terms of inhibition by sulfonylureas, imidazolonones, triazolopyrmidines, salicylated, and carbamoylpyrazolines, imidazolinones, triaiolopyritnidines, salicjdates, and carbarnoylpj?razolines, respectively. All five types show biphasic slow tight binding kinetics with Stedy state I₅₀values of 0.5 nm (sulforneturon), 1.9 nm (triazolopjirimidine), 8.3 nm (salicylate), 23 nm (imazapyr), and 135 nm (carbamoylpyrazoline),respectiuely . Isolated ALS from Saccharomyces cerevisiae is equallv well blocked by herbicidal ALS inhibitors although with different I₅₀values ( triazoiopyrimidine, 21 nm, sulforneturon, 70 nm, salicylate, 21 μm, imaiapyr, 38μm, and carbamoylpyrazoline, 148 μm ). Surprisingly, biphasic kinetics could not be observed with the yeast enzjtme although slow binding hehauiour was clearly established.     

Correlation of physico‐chemical parameters with toxicity of metal ions to plants

The in vivo toxicities of 12 metal ions to cabbage plants have been correlated with ion‐specific physico‐chemical parameters. Several regression models were statistically significant but two different electronegativities in combination with Kaiser's electrochemical potential appeared to be the best determinants of metal ion toxicity, giving a good correlation (r²adjusted = 0.81 for 11 metal ions excluding copper, and 0.66 for all 12 metal ions). © 2000 Society of Chemical Industry     

嘌呤氧基苯氧丙酸酯的合成及除草活性

以4,6-二氯-5-硝基嘧啶为起始原料,经过还原胺化、取代、醚化等一系列反应,得到11个未见文献报道的嘌呤氧基苯氧丙酸酯类化合物1a~1k,其结构经1H NM R和M S确认。初步生物活性测定表明:在200 mg/L下,所有目标化合物均表现出一定的除草活性,其中化合物1f((R)-2-(4-((9-(4-氯苯)-8-(三氟甲基-9H-嘌呤-6-基)氧)苯氧)丙酸丁酯)和1h((R)-2-(4-((9-(4-氯苯)-8-(三氟甲基-9H-嘌呤-6-基)氧)苯氧)丙酸乙酯)对靶标的抑制率几乎都达到100%。     

吡唑酰胺基脲类化合物的合成及除草活性

根据活性结构拼接原理,以1-甲基-3-乙基-5-吡唑甲酰肼为起始原料,设计合成了19个新吡唑酰胺基脲类衍生物,其结构均经过核磁共振氢谱、红外光谱、质谱和元素分析确证。生物活性测试结果表明:大部分化合物对双子叶杂草苘麻Abutilon theophrasti、反枝苋Amaranthus retroflexus以及凹头苋A.ascedense显示出较好的除草活性及选择性,如在2 250 g/hm2的剂量下,3i在苗后和苗前处理时,对苘麻和反枝苋的抑制率都达到了100%。复筛的结果表明,在375 g/hm2下,3i对双子叶杂草表现出中等除草活性。     

Inhibitors of shikimate dehydrogenase as potential herbicides

Shikimate dehydrogenase (E.C. 1.1.1.25) is found in plants but not in animals and is therefore an attractive target for a new herbicide. A series of 1,6-dihydroxy-2-oxoisonicotinic acid derivatives was prepared and shown to inhibit the enzyme reversibly. Weak active-site directed irreversible inhibitors based on these compounds were also synthesised but none was herbicidal.     

Effects of different management practices on Portulaca oleracea emergence in soyabean

Portulaca oleracea (common purslane) is a summer annual weed with wide geographic distribution and is problematic in many crops worldwide. Field experiments were conducted to determine the effects of different management practices on P. oleracea emergence in soyabean fields. Two tillage systems [conventional tillage (CT) and no‐till (NT)], three soyabean seeding rates (SR) (200 000, 300 000 and 400 000 seeds ha^?1) and three imazethapyr doses (0, 50, and 100 g a.i. ha^?1 applied pre‐emergence) were considered as experimental factors. Portulaca oleracea emergence was affected by management practices including tillage system, soyabean SR and imazethapyr dose. Conventional tillage required a thermal time (TT) of 195.95 and 221.30 d °C to reach 50% emergence in 2016 and 2017, respectively, while for NT, the respective TT requirements were 182.34 and 203.32 d °C. On increasing soyabean SR from 200 000 to 400 000 seeds ha^?1, the TT requirements for 50% emergence (T₅₀) of P. oleracea also increased. The T₅₀ at the herbicide dose of 100 g a.i. ha^?1 was 193.05 and 220.67 d °C in 2016 and 2017, respectively, while for the non‐herbicide treatment, the respective TT requirements were 165.98 and 202.94 d °C. From an integrated weed management perspective, a combination of CT with a SR of 400 000 seeds ha^?1 and a 100 g a.i. ha^?1 imazethapyr dose not only resulted in the lowest P. oleracea seedling density m^?2 but also caused the longest delay in the time to reach the T₅₀. Findings from our study may facilitate the development of effective P. oleracea management strategies.     

1,3,4(2H)-isoquinolinetrione herbicides: Novel redox mediators of photosystem I

A series of 1,3,4(2H)-isoquinolinetriones have been found to be fast-acting post-emergence herbicides, producing symptoms of desiccation. These redox-active compounds are very potent stimulators of the light-dependent consumption of oxygen at photosystem I in isolated chloroplasts. Pulse radiolysis studies on 2-ethyl-1,3,4(2H)-isoquinolinetrione have shown it to have free-radical properties which could enhance the generation of superoxide radicals in plants. Electrochemical studies further support a redox mediator mode of action for the series. The compounds were found to be unstable towards hydrolysis, and this was considered to be a major factor limiting the overall herbicidal effects. Other parameters, related to uptake and/or translocation, which may limit the full expression of the herbicidal activity of certain compounds, are discussed.     

2-苄硫基烟酰胺类衍生物的合成及生物活性

以2-苄硫基烟酸为原料,设计并合成了26个2-苄硫基烟酰胺类化合物,其化学结构经核磁共振氢谱和元素分析确证。初步的生物活性测定结果表明,该类化合物具有一定的杀虫及除草活性。其中 C-9、C-10、C-11 在50 mg/L时对淡色库蚊Culex pipiens pallens的致死率达到100％; C-3、C-6、C-15 在100 mg/L对稗草Echinochloa crusgalli Link、马唐Digitaria sanguinalis、苋菜Ambrosia tricolor Linn的白化度大于80％。     

Synthesis and herbicidal activities of novel 3-(substituted benzyloxy or phenoxy)-6-methyl-4-(3-trifluoromethylphenyl)pyridazine derivatives

BACKGROUND: 4‐(3‐Trifluoromethylphenyl)pyridazine represents a new series of compounds with bleaching and herbicidal activities. RESULTS: A total of 43 novel 3‐(substituted benzyloxy or phenoxy)‐6‐methyl‐4‐(3‐trifluoromethylphenyl)pyridazine derivatives were synthesised, and their bleaching and herbicidal activities were evaluated through Spirodela polyrrhiza and greenhouse tests. Some compounds exhibited excellent herbicidal activities, even at a dose of 7.5 g ha^?1. CONCLUSION: The results showed that a substituted phenoxy group at the 3‐position of the pyridazine ring and the electron‐withdrawing group at the para ‐position on the benzene ring were essential for high herbicidal activity. Copyright © 2011 Society of Chemical Industry     

棉籽壳中除草活性物质提取及鉴定

为了开发利用棉籽壳中的除草活性物质,分别以无水乙醇、正丁醇、石油醚和乙酸乙酯为溶剂,采用索氏提取法对棉籽壳中的活性物质进行了提取,并对各溶剂粗提物进行了除草活性测定。结果发现:用无水乙醇提取的粗提物对稗草生长的抑制活性最高,经气相色谱-质谱(GC-MS)联用分析,发现该粗提物中主要含有甘油、三环己基3-烯-6-辛酮、4-乙烯基-2-甲氧基苯酚、(邻甲基苯酚)-2-溴-2氯-乙酰酯、十四酸、十四酸乙酯、十六烷酸、辛酸异戊酯和亚油酸9种化合物。进一步的除草活性测定结果表明,亚油酸、辛酸异戊酯、4-乙烯基-2-甲氧基苯酚和(邻甲基苯酚)-2-溴-2氯-乙酰酯4种化合物对稗草表现出一定的除草活性,其中亚油酸活性最强,其IC₅₀值为14.5 mg/L。     

N-(7-氟-3-氧-3,4-二氢-苯并噁嗪-6-基-)乙酰胺类化合物的合成及除草活性

为了寻找高效、安全的具有除草活性的新化合物,利用2-取代乙酰氯和2H苯并噁嗪-3-酮反应合成了9个N-(7-氟-3-氧-3,4-二氢苯并噁嗪-6-基-)乙酰胺类化合物,其结构经元素分析、IR、1H NMR确证。初步除草活性测试表明:在有效剂量75 g/hm2下,化合物 5d 芽后茎叶处理对刺苋Amaranthus spinosus等4种杂草显示出90%以上的抑制率。     

Fe<Superscript>2+</Superscript> and Mn<Superscript>2+</Superscript>, potential agents to induce suppression of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> for biological soil disinfestation

Here Fusarium oxysporum was killed in exudates obtained from soil biologically disinfested with ethanol, indicating that physical interaction with soil microorganisms was not essential. Because acetic acid was confirmed to accumulated during the treatment, we evaluated the effect of acetic acid amendment against the pathogen in plastic containers. A drop in the soil redox potential seemed to be correlated with the fungicidal efficacy of acetic acid. Under reductive soil conditions, metal ions such as Mn²⁺ and Fe²⁺ formed, and the pathogen was effectively suppressed in Mn²⁺ and Fe²⁺ solution. Therefore, Fe²⁺ and Mn²⁺ may be the agents that induce suppression of the pathogen during biological soil disinfestation.     

Enzymatic hydrolysis of diazoxon by rat tissue homogenates

The enzymatic hydrolysis of ³²P-labeled diazoxon was studied using tissue homogenates of rat and American cockroach. The order of the hydrolytic activities of rat tissues for diazoxon was as follows: liver > blood > lung > heart > kidney > brain. A liver enzyme hydrolyzing diazoxon to diethyl phosphoric acid and 2-isopropyl-4-methyl-6-hydroxypyrimidine was located in the microsomes. The activity of the microsomal enzyme was inhibited by EDTA, heavy and rare earth metal ions, and SH reagents. Ca²⁺ activated the enzyme and protected it from inactivation. Mitochondrial and soluble enzymes from liver and a serum enzyme also hydrolyzed diazoxon and they were also activated by Ca²⁺. The removal of calcium bound to the microsomal enzyme protein by dialysis against EDTA led to a partially irreversible change of the enzyme. The hydrolysis of diazoxon by the Ca²⁺-requiring microsomal and serum enzymes was more rapid than that of paraoxon. Hydrolysis of diazoxon did not occur in American cockroach homogenates. This difference in the capacity to hydrolyze diazoxon between mammals and insects is discussed in relation to the selective toxicity of diazinon.     

Complex formation of picloram and related chemicals with metal lons

The complex formation of metal ions with pyridine carboxylic acids was estimated with polarography and spectrophotometry. Picloram (4-amino-3,5,6-trichloropicolinic acid), α-picolinic acid, fusaric acid, dipicolinic acid, and quinolinic acid formed complexes with Fe(III) or Cu(II) whose coordination involves, most probably, a lone pair of electrons of pyridine nitrogen and a carboxylic group. Picloram-metal complexes were, however, estimated to be relatively unstable compared to other pyridine-α-carboxylic acids tested. Effects of pyridine carboxylic acids on oxidation of indole-3-acetic acid (IAA) were tested in vitro in a horseradish protoheme peroxidase system. No significant effect of the pyridine carboxylic acids was observed at 2 × 10^?4M. Also, no concentration effect of picloram (10^?5 to 3 × 10^?3M) was obtained. These results suggest that the phytotoxic action of picloram may not result from the depletion of free metal ions in plants nor inhibition of activity of metal-containing enzymes through strong chelation as hypothesized. Thus, auxin activity of picloram should be explained in other wasy.     

Imazethapyr inhibition of acetolactate synthase in Rhizobium and its symbiosis with pea

Acetolactate synthase (ALS) activity extracted from Rhizobium leguminosarum biovar. viciae has been characterized. The optimum pH for extraction was 7·6 and for the assay 7·0. The K_m for pyruvate was 7·2 mM , and the enzyme was saturated at 40 mM . An obligatory requirement of TPP and Mg²⁺ for full ALS activity was observed. Valine was the only branched-chain amino acid that caused ALS feedback inhibition. The specific activity of Rhizobium ALS was nearly 20 times the activity found in pea (Pisum sativum) leaves. Bacteroids from pea nodules also showed high ALS activity, and the nodule plant fraction had higher ALS activity than other plant tissues. ALS sensitivity to imazethapyr was also dependent on the source: ALS activity of free-living Rhizobium and bacteroids was slightly more tolerant than that of other pea tissues, but the differences were less than those found in rates of specific activity. It is proposed that the high ALS activity expressed by Rhizobium, both as free-living bacteria and as bacteroids, is related to the growth tolerance of rhizobia to imazethapyr and is also related to the relative tolerance of symbiotic pea plants. © 1998 SCI