Development and molecular analysis of a novel acetohydroxyacid synthase rapeseed mutant with high resistance to sulfonylurea herbicides

With the increasing promotion of simplified rapeseed cultivation in recent years,the development of cultivars with high resistance to herbicides is urgently needed.We previously developed M342,which shows sulfonylurea herbicide resistance,by targeting acetohydroxyacid synthase(AHAS),a key enzyme in branched-chain amino acid synthesis.In the present study,we used a progeny line derived from M342 for an additional round of ethyl methane sulfonate mutagenesis,yielding the novel mutant DS3,which harbored two mutations in AHAS genes and showed high sulfonylurea resistance.One mutation was the substitution Trp574 Leu,as in M342,according to Arabidopsis protein sequencing.The other site was a newly recognized substitution,Pro197 Leu.A KASP marker targeting Pro197 Leu was developed and reliably predicted the response to sulfonylurea herbicides in the F2 population.The combination of Trp574 Leu and Pro197 Leu in DS3 produced a synergistic effect that greatly increased herbicide resistance.Analysis of the protein structures of AHAS1 and AHAS3 in wild-type and single-gene mutant plants revealed three-dimensional protein conformational changes that could account for differences in herbicide resistance characteristics including toxicity tolerance,AHAS enzyme activity,and AHAS gene expression.

Metsulfuron-methyl Molecularly Imprinted Stir Bar Sorptive Extraction Coupled with High Performance Liquid Chromatography for Trace Sulfonylurea Herbicides Analysis in Complex Samples

Metsulfuron-methyl molecularly imprinted polymer（MIP）-coated stir bar was prepared for sorptive extraction of sulfonylurea herbicides in complex samples.The MIP-coating was about 21.3 μm thickness with the relative standard deviation（RSD） of 4.4%（n=10）.It was homogeneous and porous with good thermal stability and chemical stability.The extraction capability of the MIP-coating was 2.8 times over that of the non-imprinted polymer（NIP）-coating in hexane.The MIP-coating exhibited selective adsorption ability to the template and its analogues.The extraction conditions,including extraction solvent,desorption solvent,extraction time,desorption time and stirring speed,were optimized.A method for the determination of six sulfonylurea herbicides by MIP-coated stir bar sorptive extraction coupled with high performance liquid chromatography（HPLC） was developed.The linear range was 10―200 μg/L and the detection limits were within a range of 2.0―3.3 μg/L.It was also applied to the analysis of sulfonylurea herbicides in spiked river water,soil and rice samples.

Rapid Residue Analysis of Sulfonylurea Herbicides in Surface Water: Methodology and Residue Findings in eastern Tiaoxi River of China

A new method combining QuEChERS (quick, easy, cheap, effective, rugged and safe) and DLLME (dispersive liquid–liquid microextraction) for the simultaneous determination of residues of ten sulfonylurea herbicide in water using UPLC-MS/MS was developed and validated. Analytes were extracted and purified with QuEChERS and concentrated in chlorobenzene by applying the DLLME procedure. Several extraction parameters were tested, such as volume, extractive solvent by the QuEChERS method and subsequently used for DLLME, selection of extractive solvent and its volume, was tested. The developed method was validated on the basis of international guidelines. Mean recoveries ranged from 81.2 to 104.9%. Repeatability and reproducibility were lower than 10%. Limits of detection (LODs) and quantification (LOQs) were below 0.074 μg/L and 0.244 μg/L, respectively. Decision limit (CCα) and detection capability (CCβ) were calculated and CCβ ranged from 0.101 μg/L (pyrazosulfuron-ethyl) to 0.260 μg/L (nicosulfuron). Finally, when the method was applied to real samples, traces of three compounds were found in 42 samples and only thifensulfuon-methyl was detected above the LOQ in three samples at 0.17-0.20 μg/L.

2D-and 3D-QSBR Study on the Relationship between the Structure and Biodegradation Property of Sulfonylurea Herbicides

Using DFT method, 10 sulfonylurea herbicides were computed at the B3LYP/6- 31G＊ level. Based on linear solvation energy theory, the corresponding linear solvation energy relationship （LSER） equation （R2 -- 0.759） to the half-life time （T1/2） of biodegradation was obtained with the structural and thermodynamic parameters as theoretical descriptors. Furthermore, CoMSIA method was also applied to establish 3D models which reveal the fields influencing these properties. The relationship between the properties and the structure was obtained. And the related coefficient of the model is 0.952. Results showed the electronic property is important to affect the biodegradation of these compounds by analysis of the 2D and 3D models.

Enzymatic activity and chlorophyll fluorescence imaging of maize seedlings (Zea mays L.) after exposure to low doses of chlorsulfuron and cadmium

The aim of this research was to study the influence of chlorsulfuron residue and cadmium on the enzymatic activity and photosynthetic apparatus of maize(Zea mays L.) plants. Chlorsulfuron and cadmium at 0.001 and 5.0 mg kg–1, respectively, were mixed and applied to soil prior to planting. The levels of chlorsulfuron-and cadmium-induced stress to plants were estimated by growth, chlorophyll content, lipid peroxide content, enzyme activities, and major fluorescence parameters of chlorophyll(revealed by the fluorescence imaging system Fluor Cam). Chlorsulfuron negatively affected the chlorophyll content, photochemical efficiency of photosystem II in the dark-adapted state, the maximum efficiency of photosystem II, photochemical quenching coefficient, and steady-state fluorescence decline ratio in the leaves of maize seedlings. However, cadmium did not produce noticeable changes. Plants that were exposed to both chlorsulfuron and cadmium showed an obvious increase in the steady-state fluorescence decline ratio. These results implied that the seedlings possessed more resistance to cadmium than to chlorsulfuron and their resistance to chlorsulfuron toxicity was enhanced by the presence of cadmium. The results also suggested that chlorophyll fluorescence imaging reveals overall alterations within the leaves but may not reflect small-scale effects on tissues, as numeric values of specific parameters are averages of the data collected from the whole leaf.

Herbicide activity of monosulfuron and its mode of action

Monosulfuron was developed for weed control in the field of wheat(Triticum, aestivum L.) and millet(Panicum miliaceum L.) with the application rate ranging from 15 to 60 g ai/hm2. Herbicidal activity of monosulfuron was evaluated systematically by bioassay using maize(Zea mays L.) taproot as indicator and weed fresh weight of Acalypha australis L. and Echinochloa phyllopogon. Maize CAU 3138 was the most tolerant cultivars to monosulfuron with IC_ 50(concentration of 50% inhibition) of 85 μg/kg, Yedan 13 was one of the most sensitive cultivars to monosulfuron with IC_ 50 of 6.4 μg/kg. Monosulfuron inhibited the growth of Acalypha australis L. strongly comparing with that of Echinochloa phyllopogon. Monosulfuron was a good acetolactate synthase(ALS) inhibitor in vitro, the I_ 50(50% of inhibition) of monosulfuron, chlorsulfuron, tribenuron-methyl and nicosulfuron for CAU 3138 were 32, 2, 19 and 26 nmol/L respectively, for Yedan 13 the I_ 50 were 15, 3, 17 and 65 nmol/L respectively. In vivo ALS inhibition occurred only in higher concentration of 4 sulfonylurea herbicide tested. Comparison study of this test indicated that the mode of action of monosulfuron was the same as that of other sulfonylurea herbicides such as chlorsulfuron, tribenuron-methyl and nicosulfuron, they were all inhibitors targeted at the ALS.

Precise base editing of non-allelic acetolactate synthase genes confers sulfonylurea herbicide resistance in maize

Single-nucleotide polymorphisms contribute to phenotypic diversity in maize. Creation and functional annotation of point mutations has been limited by the low efficiency of conventional methods based on random mutation. An efficient tool for generating targeted single-base mutations is desirable for both functional genomics and precise genetic improvement. The objective of this study was to test the efficiency of targeted C-to-T base editing of two non-allelic acetolactate synthase(ALS) in generating sulfonylurea herbicide-resistant mutants. A CRISPR/Cas9 nickase-cytidine deaminase fused with uracil DNA glycosylase inhibitor(UGI) was employed to achieve targeted conversion of cytosine to thymine in ZmALS1 and ZmALS2. Both protoplasts and recovered mutant plants showed the activity of the cytosine base editor, with an in vivo efficiency of up to 13.8%. Transgene-free edited plants harboring a homozygous ZmALS1 mutation or a ZmALS1 and ZmALS2 double mutation were tested for their resistance at a dose of up to 15-fold the recommended limit of chlorsulfuron, a sulfonylurea herbicide widely used in agriculture. Targeted base editing of C-to-T per se and a phenotype verified in the generated mutants demonstrates the power of base editing in precise maize breeding.

Efficacy of Trifluralin Compared to Ethalfluralin Applied Alone and Co-Applied with Halosulfuron for Weed Management in White Bean

There are a limited number of herbicides registered for weed management in white bean production in Ontario, Canada. Five field experiments were completed in Ontario from 2016 to 2018 to compare the efficacy of trifluralin and ethalfluralin applied alone and in combination with halosulfuron, applied preplant incorporated (PPI), for weed control efficacy and white bean tolerance and seed yield. At 2 and 4 WAE, there was no white bean injury from the herbicide treatments evaluated. Trifluralin applied PPI provided up to 32%, 99%, 13%, 99%, 27%, 99% and 99% control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail, respectively. Trifluralin and ethalfluralin provide similar control of velvetleaf, redroot pigweed, barnyardgrass and green foxtail control, however, ethalfluralin is slightly more efficacious on common ragweed, common lambsquarters and wild mustard. Halosulfuron (35 g∙ai∙ha−1), applied PPI, provided as much as 76%, 98%, 96%, 96%, 100%, 19% and 23% control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail, respectively. Trifluralin (600 or 1155 g∙ai∙ha−1) + halosulfuron (35 g∙ai∙ha−1), applied PPI, provided up to 88%, 100%, 98%, 100%, 100%, 99% and 98% control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail, respectively. Ethalfluralin (810 or 1080 ai∙ha−1) + halosulfuron (35 g∙ai∙ha−1) provided similar control. Weed interference decreased white bean seed yield 44% - 45% with trifluralin, 30% - 41% with ethalfluralin and 34% with halosulfuron. However, decreased weed interference with trifluralin and ethalfluralin applied in combination with halosulfuron resulted white bean seed yield that was similar to the weed-free control. Trifluralin or ethalfluralin co-applied with halosulfuron can be safely used in white bean production for the control of common annual grass and broadleaf weeds in Ontario.

Design, Synthesis and Herbicidal Activity of Novel Sulfonylureas Containing Tetrahydrophthalimide Substructure

To develop novel sulfonylurea herbicides, a series of chlorsulfuron derivatives was designed and synthesized through introducing tetrahydrophthalimide substructure taken from protoporphyrinogen IX oxidase（PPO） inhibitors onto the critical 5-position of the classical benzene ring. The structures of title compounds were confirmed by infrared spectroscopy, ultraviolet spectroscopy, 1H and 13C NMR spectrometry, mass spectrometry and elemental analysis. In addition, the crystal structure of compound I1-5 was further determined by X-ray diffraction analysis. Bioassay results showed that individual compounds exhibited good herbicidal activities, especially compound I1-8, which displayed 100% inhibition rate against Echinochloa crusgalli at 150 g/ha（1 ha=104 m2） with the method of foliage spray in the pot experiment.

Controllable Effect of Structural Modification of Sulfonylurea Herbicides on Soil Degradation

The study of soil degradation behaviors of sulfonylurea herbicides in relation to their different structural attributes is utmost important for us to comprehend the development of new eco-friendly herbicides. It is postulated that the structural modification of the chemical structures could influence their degradation rates in soil. Nine devised structures were synthesized to study their herbicidal activity as well as their soil degradation behaviors respectively. The novel compounds I-3-I-7 were characterized by UV, ^1H NMR and ^13C NMR, MS and EA. Bioassays indicated that most of target compounds displayed superior herbicidal activities in comparison with Chlorsulfuron. Soil degradation results further confirmed our previous assumption that the introduction of electron-donating substituents at 54 position of the benzene ring distinctly increased their degradation rates, among which dimethylamino and diethylamino groups can adjust the degradation rate to a more favorable status.

Synthesis and Herbicidal Activity of Novel Sulfonylureas Containing 1,2,4-Triazolinone Moiety

A series of new sulfonylureas incorporating 1,2,4-triazolinone moiety was synthesized, which were further bio-assayed for the herbicidal activity against four herbs, representative of monocotyledons and dicotyledons. Some of them exhibited high potency to inhibit the growth of dicotyledons（Bassica napus and Arnaranthus retroflexus） in the pot experiment. Compounds 9a and 9b also displayed an excellent herbicidal activity against Bassica napus at a concentration of 15 g/hectare, which were comparable with commercial triasulfuron.

Gas-phase Smiles Rearrangement of Sulfonylurea Herbicides in Electrospray Ionization Mass Spectrometry

In the negative ion mode of electrospray ionization tandem mass spectrometry （ES1-MS/MS） of four sulfonyl- urea herbicides, Smiles rearrangements were observed in rimsulfuron and nicosulfuron. In the case of rimsulfuron, two competitive gas-phase Smiles rearrangements initiated by nitrogen anion and oxygen anion respectively were witnessed. The ion-neutral complex was proposed as the reactive intermediate in the course of this unimoleeular dissociation reaction of the oxygen attack Smiles rearrangement route. The density functional theory （DFT） was carried out to elucidate the mechanism as well as to show the possible transition states and the intermediates.

Non-hydrolytic Sol-gel Methodology to Prepare a Molecularly Imprinted, Organic-silica Hybrid-based Stir Bar for Recognition of Sulfonylurea Herbicides

Based on a molecularly imprinted organic-silica hybrid-based stir bar, a pre-treatment methodology was devel- oped for enrichment of nicosulfuron in aqueous samples. The molecularly imprinted organic-silica hybrid-based coating on the outer surface of a glass stir bar was prepared by in-situ polymerization using nicosulfuron as a template molecule, a-methacrylic acid as a functional monomer, methacryloxypropytrimethoxysilane as a cross-linker in the mixture of acetonitrile and trichloromethane （V/V, 7.5 ： 1）. To achieve the selective extraction of the target analyte from aqueous samples, several main parameters, including extraction time, pH value and contents of inor- ganic salt in the sample matrix were investigated. Evidence was also presented by the scanning electronic micro- scopic images of the imprinted and non-imprinted stir bars. Then, the extraction efficiency of the stir bar was tested with separate experiments and competitive sorption experiments. These results showed that using six sulfonylureas as substrates the molecularly imprinted organic-silica hybrid-based stir bar gave high selectivity for the template, nicosulfuron compared to the non-imprinted organic-silica hybrid-based stir bar. This sorption extraction was cou- pled to liquid chromatography ultraviolet detection allowing the determination of nicosulfuron from tap water. The method showed good recoveries and precision, 96.0% （RSD 2.7%, n=3） for tap water spiked with 0.125 nmol （25.00 mL sample）, suggesting that the stir bar can be successfully applied to the pre-concentration of nicosulfuron in real aqueous samples.

Functional biochar for efficient residue treatment of sulfonylurea herbicides by weak molecular interaction

Pesticide residues have seriously damaged the natural environment and social security.Here,we prepared the efficient functional biochar(FB)for sulfonylurea herbicides from cotton straw cellulose(CSC)by hydrothermal carbonization with the methacrylic acid.The molecular simulation of FB indicated thatπ-πelectron-donor-acceptor(EDA)interaction and formation of charge-assisted H-bond were both the main factors for effective adsorption process.The adsorption process can match the pseudo-second-order kinetic equation and Freundlich model.The whole process is physical adsorption,spontaneous and rapid,and can quickly reach equilibrium.The FB with carbon-oxygen functional groups and aromatic conjugated structures can remove pesticides in water very quickly(within 30 s),with effective adsorption over 95%of Sulfonylurea herbicides(SUHs).Therefore,functional FB might be an effective way to get excellent absorbent for pesticide treatment.

Ultimate fate of halosulfuron methyl and its effects on enzymatic and microbial activities in three differently textured soils

Halosulfuron methyl is a sulfonylurea herbicide used worldwide for weed control in sugarcane, maize, wheat, and rice production. Considering its environmental impact, this study evaluated the effects of soil type, application rate, and temperature on the dynamics of halosulfuron methyl degradation.Additionally, as soil microbes and enzymes are reliable indicators of the impacts of anthropogenic activities on soil health, the effects of halosulfuron methyl on soil enzymatic and microbial activities were also assessed. The half-life(DT50) of halosulfuron methyl varied from 9.38 to 33.77 d. Increase in temperature accelerated the degradation and DT50 varied from 14.39 to 33.77, 11.05 to 28.94, and 9.38 to 25.41 d at 5, 15, and 25?C, respectively. The metabolites of halosulfuron methyl, including halosulfuron, methyl 3-chloro-5-((4,6-dimethoxy-2-pyrimidinyl) amino)-1-methyl-1H-pyrazole-4-carboxylate,4,6-dimethoxy-2-pyrimidinamine, and methyl 3-chloro-1-methyl-5-sulfamoyl-1H-pyrazole-4-carboxylate, were detected in the studied soils, and their appearance and disappearance varied with application rate, soil type, and incubation temperature. Halosulfuron methyl had transitory harmful effects on soil enzymatic and microbial activities depending on its application rate. The results suggest that the application rate of halosulfuron methyl, soil physicochemical parameters, and temperature should be considered together to ensure satisfactory weed control with reduced environmental risk.

Research on controllable alkaline soil degradation of 5-substituted chlorsulfuron

Sulfonylurea（SU） has become one class of the most important herbicides worldwide due to their ultralow application rate and mammalian toxicity. Recently application licenses of 3 classical SU herbicides chlorsulfuron, metsulfuron-methyl and ethametsulfuron were suspended due to their undesirable long persistence which is incompatible with the particular rotation planting system in China. Our previous study has discovered that electron-donating groups, especially dimethylamino and diethylamino substituents, on the 5 th position of the benzene ring in chlorsulfuron, greatly accelerated its degradation rate in an acidic soil（p H 5.41）. Owing to the natural slower degradation of SUs in alkaline soil,dimethylamino and diethylamino substituted chlorsulfuron Ia and Ib were further studied in an alkaline soil（p H 8.46） with chlorsulfuron as a control. The experimental data indicated that the half-life of degradation（DT50） of Ia was 3.36 days while Ib was 6.25 days which amounted to 30 and 15 folds faster than chlorsulfuron（DT5084.53 days）, respectively. The research confirmed that our newly-designed structures Ia and Ib can hasten their degradation rate in alkaline soil as well as in acidic soil. This structural modification of the classical SU provided an opportunity to control the degradation rate to reduce their impact on relevant environment and ecology.