Mode of action of famoxadone

Famoxadone is a preventative and curative fungicide recently developed for plant disease control. The molecule and its oxazolidinone analogs (OADs) are potent inhibitors of mitochondrial electron transport, specifically inhibiting the function of the enzyme ubiquinol:cytochrome c oxidoreductase (cytochrome bc₁). Visible absorbance spectral studies on the purified enzyme suggested that famoxadone bound close to the low potential heme of cytochrome b. This binding mode was confirmed in competitive binding experiments by studying the displacement of a radiolabelled OAD from submitochondria. EPR studies on the binding of famoxadone to submitochondria and purified bc₁ suggested its binding mode was more like that of myxothiazol than that of stigmatellin (ligands known to bind near the low potential heme). Zoospores of Phytophthora infestans, when given low concentrations of famoxadone and other OADs, were observed to cease oxygen consumption and motility within seconds and later the cells disintegrated, releasing the cellular contents. Famoxadone was a potent inhibitor of the growth of Saccharomyces cerevisiae when grown on non-fermentable carbon sources and it was an approximately 50-fold less potent inhibitor of growth when the yeast was grown on a fermentable carbon source, glucose. Such physiological observations are consistent with the loss of mitochondrial function imposed by famoxadone and OADs. Single amino acid changes in the apocytochrome b of baker's yeast cytochrome b located near the low potential heme altered the inhibition constants for the inhibitors famoxadone, myxothiazol, azoxystrobin and kresoxim-methyl differentially, thus strongly suggesting different binding interactions of the protein with the inhibitors. © 1999 Society of Chemical Industry     

Fate of famoxadone in the environment

The fate of famoxadone [Famoxate®, 3-anilino-5-methyl-5-(4-phenoxyphenyl)-1,3-oxazolidine-2,4-dione] in the aquatic and soil environment was examined. It was found to be relatively stable at pH 5, but hydrolysed rapidly in pH 7 and 9 buffer solutions. Primary hydrolytic degradation reactions included the opening of the oxazolidinedione ring and the cleavage of the oxazolidinedione-aminophenyl linkage. The compound degraded rapidly in soil by both hydrolytic and microbial action. In addition to the generation of [¹⁴C] carbon dioxide and unextractable bound residues, hydroxylation and hydrolysis reactions occurred to yield multiple degradation products. Nitration of famoxadone at the 2- or 4-phenylamino position was observed as a novel non-biological degradation reaction of famoxadone in soil. Degradation in aqueous solution (pH 5) and on soil surfaces was accelerated under simulated sunlight irradiation. Famoxadone exhibited negligible soil mobility potential, and its primary degradation products were also shown to dissipate rapidly in the environment.     

SODM、DTA-6及Cc对马铃薯叶片碳代谢相关生理指标的影响

大田栽培条件下,以马铃薯（Solanum tuberosum L.）荷兰212为材料,叶面喷施不同植物生长调节剂,测定叶片中蔗糖、蔗糖转化酶活性、淀粉、淀粉酶活性变化以及可溶性糖、还原糖等含量的变化,研究喷施植物生长调节剂对马铃薯叶片碳代谢生理指标的影响。结果表明：喷施SOD模拟物（简称SOD_M）后16天叶片中可溶性糖、蔗糖以及淀粉的含量显著提高,24天和32天后还原糖含量明显增加;氯化胆碱（Choline chloride, 简称Cc）能够极显著降低处理后32天时叶片的转化酶活性,也可以显著提高处理后24天和32天时还原糖的含量;2-N,N-二乙氨基乙基己酸酯（Diethyl aminoethyl hexanoate,简称DTA-6）能够极显著提高使用后16天时淀粉的含量,同 时其对处理后24～32天淀粉酶活性有极显著降低的作用。     

螺虫乙酯在染毒雄性大鼠体内的分布与代谢

建立了采用超高效液相色谱-串联质谱仪(UPLC-MS/MS)检测不同动物样品中螺虫乙酯及其主要代谢物残留量的方法,并研究了螺虫乙酯在大鼠体内的吸收与代谢。样品中螺虫乙酯及其主要代谢物经甲醇提取及C18固相萃取(SPE)柱净化后,用UPLC-MS/MS检测。结果显示,所建立方法快速、灵敏,每个样品上机检测仅需3 min,方法的最低检出浓度(LOQ)为0.005 mg/kg。对按照每千克体重每日250 mg剂量染毒28 d后的大鼠体内螺虫乙酯残留量的检测结果表明:螺 虫乙酯在睾丸、肝脏、肺、肾、心脏、血浆等器官和组织中的残留量较低,平均在0.012~0.025 mg/kg 之间,且分布差异不显著,而脂肪和肌肉中螺虫乙酯的残留量显著低于睾丸和肝脏中的残留量(P P 肾>血浆>肺>心脏>睾丸>脂肪>肌肉。     

AAL-toxin,a potent natural herbicide which disrupts sphingolipid metabolism of plants

AAL-toxin, a product of Alternaria alternata (Fr.) Keissl., is effective as a herbicide at low concentrations against a range of broadleaf plants (e.g. jimsonweed, prickly sida and black nightshade). However, monocotyledonous crops such as maize and wheat, as well as some varieties of tomato, are tolerant to it. The IC50 values for cellular electrolyte leakage and chlorophyll loss in duckweed (Lemna pausicostata L.) after 72 h treatment were 20–40 nM. Similar results were obtained with a susceptible tomato variety. AAL-toxin caused rapid cellular leakage of electrolytes, followed by cellular collapse; the first symptom at the ultrastructural level is disruption of the plasma membrane. The effects of the toxin are not light-dependent and appear to be associated with dysfunction of the plasma membrane. Fumonisins and sphingoid bases such as phytosphingosine cause similar effects, although these compounds are less potent (fumonisins, about 10-fold; sphingoid bases, about 100-fold). Recent studies suggest that in duckweed and in susceptible tomato varieties, AAL-toxin- and fumonisin B1 -induced disruption of sphingolipid metabolism is an early event in the cascade of events leading to phytotoxic injury and cell death.     

Conserved virulence factor regulation and secretion systems in bacterial pathogens of plants and animals

Recent research has revealed the emergence of common themes in the molecular mechanisms of virulence in bacterial pathogens of plants and animals. In particular, the systems used for the global control of virulence factor synthesis and for the secretion of virulence determinants in diverse bacterial pathogens show strong conservation, implying evolutionary relatedness. Global control of virulence factor synthesis can be affected by a variety of environmental factors, bacterial hormones and programmed genetic rearrangements.Protein secretion in Gram-negative bacteria occurs via a number of targeting pathways. Type I and type III secretion systems mediate translocation across both the inner and outer membrane in a single step, while type II secretion proceeds via a periplasmic intermediate. Type II and type III secretion systems have been shown to target virulence determinants in both plant and animal bacterial pathogens.Abbreviations Cel cellulase - EPS extracellular polysaccharide - HL homoserine lactone - OHHL N-(3-oxohexanoyl)-l-homoserine lactone - PC phenotypic conversion - Pel pectate lyase - pv. pathovar - spp. species     

DTA-6、SODM及Cc对马铃薯地下主茎生长及同化物代谢生理的影响

大田栽培条件下,以马铃薯荷兰212为材料,叶面喷施植物生长物质2-N,N-二乙氨基乙基己酸酯（Diethyl aminoethyl hexanoate,简称DTA-6）、氯化胆碱（Choline chloride, 简称Cc）以及SOD模拟物(简称SOD_M),测定地下主茎鲜重、干重、蔗糖、蔗糖转化酶活性、淀粉、淀粉酶活性变化以及可溶性糖等含量的变化,研究不同植物生长物质对马铃薯地下主茎生长及碳代谢生理指标的影响。结果表明：从喷药后16 d开始,Cc和SOD_M处理均能大幅提高地下主茎蔗糖的含量,其中Cc处理平均比CK增加36.68%,SOD_M处理较CK高出30.36%。同时喷施Cc后40 d和48 d淀粉酶活性提高,平均增幅为35.11%。从喷药后32 d开始,DTA-6和Cc处理对转化酶活性也具有提高的效应,DTA-6处理平均提高了35.75%,Cc处理平均提高了34.79%,但方差分析结果表明差异不显著。另外SOD_M处理能够极显著降低块茎膨大时期地下主茎内淀粉含量,而Cc处理可极显著提高此时期地下主茎的可溶性糖含量。     

Inhibition of thiazopyr metabolism in plant seedlings by inhibitors of monooxygenases

Metabolism of the herbicide thiazopyr [methyl 2-(difluoromethyl)-5-(4, 5-dihydroO-lhiazo!vt)-4-(2-methylpropy!)-6-(trinuorornethyl)-3-pyridinecarboxy-late] was examined in young seedlings of redroot pigweed, grain sorghum, sunflower, corn and soybean. As previously observed with rat liver microsomes plants predominantly metabolized thiazopyr via oxidation reactions. Sulfur and carbon atoms in the thiazoline ring were the primary sites of plant oxygenases. De-esterification was also identified as an important pathway of transformations in plants. Although similar pathways of thiazopyr metabolism were observed among plants, our data indicated species differences in rates of thiazopyr degradation. Among species examined, pigweed (Amaranthus retroflexus L.) showed the fastest metabolism. Thiazopyr metabolism in pigweed was significantly inhibited by several cytochrome P450 monooxygenase inhibitors, among which tetcyclacis (TET) and piperonyl butoxide (PBO) were the most inhibitory. Thiazopyr metabolism in pigweed was not inhibited by organophosphates, known inhibitors of esterases. The results suggest that thiazopyr metabolism in plants is predominantly mediated via plant mono-oxygenases.     

Toxico‐kinetics,recovery efficiency and microsomal changes following administration of deltamethrin to black Bengal goats

A study of the toxico‐kinetics, recovery percentage from different substrates, cytotoxicity and role of cytochrome P₄₅₀ and b₅ of liver microsome in the metabolism of deltamethrin were carried out in female black Bengal goat. The ALD₅₀ value of deltamethrin in goat by intravenous route lies between 0.2 and 0.6 mg kg^?1. Intravenous disposition kinetics using a dose of 0.2 mg kg^?1 showed that the maximum blood concentration of deltamethrin was recorded at 0.5 min, followed by rapid decline, and a minimum concentration was detected at 6 min after administration. The following values were obtained : Vd_area 0.148 (± 0.02) litre kg^?1; t_1/2 (α) 0.22 (± 0.02) min; t_1/2 (β) 2.17 (± 0.37) min; K_el 1.05 (± 0.24) min^?1; AUC 4.30(± 0.45) µg min ml^?1; Cl_B 0.05 (± 0.006) litre kg^?1 min^?1; T～B 1.93 (± 0.58); fc 0.40(± 0.05). After 10 min, liver retained the maximum residue, and heart, adrenal gland, kidney, spleen, fat and brain also held the insecticide; liver, fat, heart and spleen retained residue after 30 min, and bone, liver and fat retained residue after 60 min of intravenous administration. Oral absorption of deltamethrin was poor and inconsistent, and approximately 65% of administered dose was recovered from faeces and gastrointestinal contents. The excretion of deltamethrin through urine was meagre, and only 0.01 and 0.013% of the administered dose was recovered after 3 and 5 days of oral administration respectively. All the tissues retained the residue after 3 days; while fat, rumen, reticulum, omasum, abomasum, large and small intestine and bone retained the residue after 5 days of oral administration; and the percentage recoveries were 1.73 and 0.027 respectively. Deltamethrin reduced the level of cytochrome P₄₅₀ content of liver microsomal pellet of goat after 5 days of oral administration. Histopathological examination of liver, kidney, heart, spleen brain and lung sections of treated goats did not reveal any pathological changes. © 2001 Society of Chemical Industry     

Determination of famoxadone, fenamidone, fenhexamid and iprodione residues in greenhouse tomatoes

BACKGROUND: Greenhouse tomato production is intended exclusively for fresh consumption. Typical greenhouse conditions provide a conducive environment for the development of different fungi, principally late blight and grey mould, that can destroy plants and fruits. For this reason, different fungicides with different sites of action are used in integrated pest management strategies. Famoxadone, fenamidone, fenhexamid and iprodione (fig. 1 ) are fungicides of difference classes with different actions that could be used to control tomato pests. RESULTS: The QuEChERS method showed good recoveries, and the analytical method allowed good separation of the fungicides selected. Good results were obtained in terms of repeatability and intermediate precision, with a coefficient of variation of < 9.8%. The limits of determination and quantification of the method were far below the maximum residual levels (MRLs) set by the EU for these fungicides in tomatoes. The analysis of fungicide residues showed that cv. Shiren accounted for higher residue levels than cv. Caramba. The dissipation curves were similar in the two cultivars, indicating that the decrease in pesticides was not related to the tomato type. CONCLUSIONS: Care should be taken when using pesticides in greenhouse conditions, because degradation mainly affects fruit growth. The size of the tomato, in particular its surface/weight ratio, is very important for defining pesticide residues. All fungicides used showed residue levels below the MRLs at the preharvest interval. Copyright © 2011 Society of Chemical Industry     

Impact of foliar nickel application on urease activity,antioxidant metabolism and control of powdery mildew (Microsphaera diffusa) in soybean plants

Nickel (Ni) is a cofactor for urease, an enzyme that breaks down urea into ammonia and carbon dioxide. This study aimed to evaluate the physiological impact of Ni on urea, antioxidant metabolism and powdery mildew severity in soybean plants. Seven levels of Ni (0, 10, 20, 40, 60, 80 and 100 g ha^?1) alone or combined with the fungicides fluxapyroxad and pyraclostrobin were applied to soybean plants. The total Ni concentration ranged from 3.8 to 38.0 mg kg^?1 in leaves and 3.0 to 18.0 mg kg^?1 in seeds. A strong correlation was observed between Ni concentration in the leaves and seeds, indicating translocation of Ni from leaves to seeds. Application of Ni above 60 g ha^?1 increased lipid peroxidation in the leaf tissues, indicative of oxidative stress. Application of 40 g ha^?1 Ni combined with 300 mL ha^?1 of fungicide reduced powdery mildew severity by up to 99%. Superoxide dismutase, catalase, peroxidase and urease enzyme activity were greatest under these conditions. Urea concentration decreased in response to Ni application. Urease activity in soybean leaves showed a negative correlation with powdery mildew severity. The leaf Ni concentration showed a positive correlation with the urease and a negative correlation with powdery mildew severity. The results of this study suggest that urease is a key enzyme regulated by Ni and has a role in host defence against powdery mildew by stimulating antioxidant metabolism in soybean plants.     

Cytochrome P450‐mediated herbicide metabolism in plants: current understanding and prospects

Cytochrome P450s (P450s) have been at the center of herbicide metabolism research as a result of their ability to endow selectivity in crops and resistance in weeds. In the last 20 years, ≈30 P450s from diverse plant species have been revealed to possess herbicide‐metabolizing function, some of which were demonstrated to play a key role in plant herbicide sensitivity. Recent research even demonstrated that some P450s from crops and weeds metabolize numerous herbicides from various chemical backbones, which highlights the importance of P450s in the current agricultural systems. However, due to the enormous number of plant P450s and the complexity of their function, expression and regulation, it remains a challenge to fully explore the potential of P450‐mediated herbicide metabolism in crop improvement and herbicide resistance mitigation. Differences in the substrate specificity of each herbicide‐metabolizing P450 are now evident. Comparisons of the substrate specificity and protein structures of P450s will be beneficial for the discovery of selective herbicides and may lead to the development of crops with higher herbicide tolerance by transgenics or genome‐editing technologies. Furthermore, the knowledge will help design sound management strategies for weed resistance including the prediction of cross‐resistance patterns. Overcoming the ambiguity of P450 function in plant xenobiotic pathways will unlock the full potential of this enzyme family in advancing global agriculture and food security. © 2020 Society of Chemical Industry     

Translocation, metabolism and residues of fluazifop-butyl in soybean plants

Translocation of fluazifop-butyl in soybean plants and hydrolysis of the ester to fluazifop-acid were investigated in a field experiment. The herbicide was translocated rapidly from the leaves to the roots, but the concentration in the leaves remained about 10-fold higher than that in the roots. Rapid hydrolysis of fluazifop-butyl to fluazifop-acid was observed, and residues of the metabolite were found to persist much longer in the plant than the active compound. Increased temperatures resulted in more rapid hydrolysis. No traces of active compound or of its main metabolite were found in the seeds after harvest. A reversed-phase HPLC method for simultaneous détérmination of fluazifop-butyl and fluazifop-acid residues in soybean plants was developed. Transport, metabolisme et residus du fluazifop-butyl chez les plantes de soja Le transport du fluazifop-butyl dans les plantes de soja et l'hydrolyse de Tester en fluazifop-acide ont étéétudiés dans une experimentation de plein champ. L'herbicide a été vehiculé rapidement des feuilles vers les racines, mais la concentration dans les feuilles est demeurée 10 fois plus haute que celle dans les racines. Une hydrolyse rapide de la forme ester en acide a été observee, et les residus du metabolite se sont reveles beaucoup plus persistants dans la plante que le composé actif. Une augmentation des températures a accéléré l'hydrolyse. Aucunes traces de la matière active ou de son principal métabolite n'ont été trouvées dans les graines après la récolte. Une methode HPLC en phase inverse pour la détérmination simultanée des residus de fluazifop-butyl et de fluazifop-acide chez le soja a été développée. Translokation, Metabolismus und Ruckstande von Fluazifop-butyl in Sojabohnen-Pflanzen Die Translokation von Fluazifop-butyl in Sojabohnen-Pflanzen und die Hydrolyse des Esters zu Fluazifop-Saure wurden in einem Freilandversuch untersucht. Das Herbizid wurde von den Blattern in die Wurzein schnell transloziert, doch in den Blattern blieb die Konzentration etwa 10mal großer als in den Wurzein. Es wurde eine schnelle Hydrolyse des Fluazifop-butyls zu Fluazifop-Saure beob-achtet, und die Ruckstande des Metaboliten in den Pflanzen erwiesen sich als viel bestandiger als der Wirkstoff. Bei hoheren Temperaturen lief die Hydrolyse schneller ab. In den Samen wurden nach der Ernte keine Ruckstande des Wirkstoffs oder seiner Hauptmetaboliten gefunden. Eine Reversed-Phase-HPLC-Methode zur gleichzeitigen Bestimmung von Ruckstanden von Fluazifop-butyl und Fluazifop-Saure in Sojabohnen-Pflanzen wurde entwickelt.     

植物生长调节剂对大豆叶片碳代谢相关生理指标的影响

在大田栽培条件下,以垦农4号大豆为材料,通过叶面喷施植物生长调节剂,比较叶片中蔗糖、转化酶、淀粉、可溶性糖、还原糖和总糖含量及转化酶活性,研究6-苄基腺嘌呤(6-BA)、脱落酸(ABA)对大豆叶片碳代谢相关生理指标的影响.结果表明:6-BA、ABA两处理在喷药后40天均提高了大豆叶片中蔗糖含量,除喷药后40d的取样期内...     

Persistence,metabolism and safety evaluation of thiamethoxam in tomato crop

BACKGROUND: Thiamethoxam, a neonicotinoid insecticide, has been widely accepted for use in various crops, including vegetables, owing to its high efficacy against various chewing and sucking insect pests. In this particular study, the authors examined the residue dynamics of this insecticide in tomato and soil and calculated a safety index for this insecticide in an Indian context. RESULTS: In tomato fruits, the insecticide dissipated from 82 to 87% in 10 days with a half‐life of 4 days, whereas dissipation in soil, under tomato crop, varied between 72 and 75% in 15 days with a half‐life of 9 days. Total residues reached below detectable level in 15 days in tomato fruits and 20 days in soil. Maximum damage (30%) was found in control plots, as opposed to 8–10% of fruit damage in treated plots. One degradation product was detected on the tomato fruit surface, and three metabolites were identified in tomato fruits by the LC‐MS technique. The metabolites have been reported for the first time in tomato fruits. CONCLUSION: Thiamethoxam at normal and double the recommended use rate effectively controlled aphids, whiteflies and Helicoverpa, as the insect population decreased to a minimum within 10 days of spraying in comparison with the control. There was no significant difference between the two rates of application, and both thiamethoxam treatments significantly increased tomato fruit yield compared with the untreated control. A maximum residue limit (MRL) of 0.05 mg kg^?1 for tomato has been proposed, with a corresponding preharvest interval (PHI) of 8 days. These parallel advances in toxicology and analytical chemistry have strengthened the observations that thiamethoxam can be used safely and efficiently in crop protection programmes. Copyright © 2009 Society of Chemical Industry     

Uptake,translocation and metabolism of the herbicide molinate in tobacco and rice

Molinate, a selective herbicide, is used for the control of annual and perennial weeds in rice paddy fields. This study was designed to assess the basis of the selective action of molinate between a susceptible broadleaf crop, tobacco, and a resistant graminaceous plant, rice. Experiments were conducted comparing plant growth under different concentrations of molinate, determining the absorption and translocation of the herbicide in the plant and identifying the metabolites in suspension cells. Rice showed greater tolerance to molinate than tobacco. Leaves of tobacco showed retarded and distorted growth at 10 mg liter^-1 of molinate 14 days after treatment, but rice leaves were unaffected at this concentration. Higher concentrations of molinate accumulating in the root of tobacco seedlings may inhibit root development and represent a significant factor in the herbicide's selective action. Seven and eight metabolites were found in tobacco and rice cells, respectively, with molinate sulfoxide and molinate sulfone present in both species. © 1998 SCI     

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.     

Acute toxicity and bioconcentration of pyrimorph in zebrafish,Brachydanio rerio

BACKGROUND: Pyrimorph is a novel fungicide being developed in China that shows high antifungal activity against diseases caused by Phytophthora infestans, Phytophthora capsici, Rhizoctonia solani, Peronophythora litchi and Pseudoperonospora cubensis. Until now, no information on the toxicity of pyrimorph to untargeted organisms has been reported. To assess the potential environmental impacts of pyrimorph in fish, the acute toxicity and bioconcentration of pyrimorph in zebrafish were studied in this paper. RESULTS: When tested by the semi‐static method, the 48, 72 and 96 h median lethal concentration (LC₅₀) values of pyrimorph to zebrafish were 24.33, 22.61 and 19.79 mg L^?1 respectively. To study the bioconcentration of pyrimorph in zebrafish, the fish were exposed to sublethal concentrations of pyrimorph (2.00 and 0.25 mg L^?1) for 192 h, a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method was applied to extract pyrimorph from samples and the residues of pyrimorph in the water and fish were determined by high‐performance liquid chromatography (HPLC). The highest bioconcentration factor (BCF) of pyrimorph in the fish was 1.07 × 10² (144 h) and 23.1 (96 h) after exposure to 2.00 and 0.25 mg L^?1 of pyrimorph respectively. CONCLUSIONS: The novel fungicide pyrimorph has low toxicity to zebrafish; however, it showed medium BCF to zebrafish. Therefore, more attention should be paid to the residue of pyrimorph in fish, as well as to its long‐term ecological effects. Copyright © 2011 Society of Chemical Industry