Herbicidal Activity Research Articles

The herbicidal activities and biochemical characteristics of isolates from Murraya microphylla

The extracts of the twigs and leaves of Murraya microphylla showed different level herbicidal activities against Amaranthus retroffexus and Digitaria sanguinalis. Bioguided isolation was performed to obtain eight pyranocarbazoles (1-8), four coumarins (10-13), two flavones (15 and 16), one dibutyl phthalate (9), and one sterol (14), including a new pyranocarbazole (1) and a new natural product (9). Petri dish assay showed that pyranocarbazoles and coumarins were the main herbicidal components of M. microphylla extract, and their structure–activity relationships were ulteriorly elucidated. As the representatives of pyracarbazole and coumarin, 7 and 10 showed significant herbicidal activity compared with the positive control (Nicosulfuron), with the IC50 values 82.93 and 16.34 μg mL−1 against shoots and roots of A. retroffexus seedling, respectively. Experimental results of morphology, physiology and biochemistry indicated that the inhibition on seed germination by 7 and 10 was mainly related to energy deficiency, while the inhibition of seedling growth was mainly related to decreased chlorophyll content, reduced root hairs, and cell membrane damage. Therefore, 7 and 10 have the potential to develop new plant herbicides directly or as lead compounds.

Encapsulation and controlled release of Streptomyces sp. herbicidal metabolites for pre-plant weed germination control

ABSTRACT Streptomyces sp. herbicidal metabolite encapsulation with controlled release properties is considered an innovative method for weed control without negatively affecting the environment. This research reports the preparation and application of new herbicidal metabolites-core/alginate-shell encapsulation systems with controlled release properties of Streptomyces sp. metabolites with pre-plant herbicidal activity for the control of weeds, Lolium perenne, Amaranthus retroflexus and Bidens pilosa showing good germination inhibition capacity. The production of Streptomyces sp. metabolites was performed by the liquid fermentation method. Three alginate polymer-coated Streptomyces sp. herbicidal metabolites-controlled release systems with an encapsulation efficiency of > 94%, were successfully prepared using the dripping extrusion method. Well-defined and compact release systems were obtained with a spherical shape and average diameters of 4.4-4.5 mm and an alginate shell thickness in the order of 400 µm with different pore sizes (26-5 µm). An increase in the alginate concentration of 0.75-2.0% (w/v) during the preparation resulted in a decrease in the shells' porosity size and a decrease in the release of the Streptomyces sp. herbicidal metabolites. The release activity of the herbicidal metabolites was evaluated by UV-Vis optical absorption spectroscopy. The statistical results showed that porous shell release systems with a lower release rate over time have a higher potential for the inhibition of germination in > 91% of weeds than the direct herbicidal metabolite application and the control group (P < 0.05). These results indicate that Streptomyces sp. herbicidal metabolites-controlled release systems represent a potentially sustainable alternative for pre-plant weed management.

Developing fluorescence hyperspectral imaging methods for non-invasive detection of herbicide safeners action mechanism and effectiveness

Herbicide safeners are considered key agents for plant protection that reduce the harmful impacts of herbicides on crops and the environment in general, but traditional evaluation methods for their effectiveness are time-consuming and labor-intensive. In this study, a rapid and non-destructive method was proposed using chlorophyll fluorescence and hyperspectral imaging that combined with machine learning models. Besides, chemometric analysis was utilized to reveal the action mechanism between the wheat crop (Triticum aestivum L.) understudy and the herbicide isoproturon (ISO) and safener gibberellin acid (GA3). The results showed that ISO caused oxidative stress and disrupted the photosynthesis mechanism in wheat by hindering the electron transport pathway from primary acceptor quinone to secondary acceptor. Meanwhile, GA3 stimulated wheat to synthesize more glutathione (GSH) that accelerated the herbicide action metabolism. It's worth noting that excessive GA3 has decreased significantly the GSH and photosynthetic pigment concentrations, while the malondialdehyde concentration was significantly (p < 0.05) increased. Additionally, competitive adaptive reweighted sampling proved the best performance when combined with partial least squares regression for predicting the phytochemical concentrations that characterized the effectiveness of GA3. In conclusion, the novelty of the current study came from the accurate real-time tracking method for GA3 action mechanism and its effectiveness on ISO toxicity. Where, that model holds great value for reducing the traditional methods' limitations in safener developments.

Bioassay‐Guided Extraction and Isolation of Natural Herbicides from Dried Zanthoxylum limonella Alston Fruits

AbstractWeeds are problematic plant species around the world. Various strategies exist for controlling weeds, but chemical treatment remains the preferred method, particularly when using natural substances. In this research, a crude aqueous‐methanol extract from dried Zanthoxylum limonella fruits was acid‐base partitioned into four fractions: neutral extract (NE), acid extract (AE), basic extract (BE), and aqueous extract (AQ). These fractions were further separated into seventeen subfractions: NEF1 to NEF7, AEF1 to AEF5, and BEF1 to BEF5, which were then tested for herbicidal activity against the growth of Chinese amaranth (Amaranthus tricolor) and barnyard grass (Echinochloa crus‐galli). Active subfractions were isolated via column chromatography and identified using spectroscopic methods, yielding seven active compounds: xanthoxyline (1), tambulin (2), atanine (3), prudomestin (4), skimmianine (5), p‐methoxybenzoic acid (6), and methyl caffeate (7). Compounds 2–7 had not been previously reported in Z. limonella. Xanthoxyline (1) was identified as the most potent botanical herbicide, fully inhibiting seed germination of Chinese amaranth and barnyard grass. This compound also decreased seed imbibition and α‐amylase activity in both species. Molecular docking studies on the α‐amylase enzyme (PDB ID: 1BG9) revealed that the aromatic, hydroxy, and carbonyl groups of xanthoxyline (1) interact with the enzyme's active sites.

Response of Palmer Amaranth Accessions in South Carolina to Selected Herbicides

Abstract Palmer amaranth resistant to dicamba, glufosinate, and protoporphyrinogen oxidase inhibitors has been documented in several southern states. With extensive use of these and other herbicides in South Carolina, a survey was initiated in the fall of 2020 and repeated in the fall of 2021 and 2022 to determine the relative response of Palmer amaranth accessions to selected preemergence (PRE) and postemergence (POST) herbicides. A greenhouse screening experiment was conducted where accessions were treated with three PRE (atrazine, s-metolachlor, and isoxaflutole) and six POST (glyphosate, thifensulfuron-methyl, fomesafen, glufosinate, dicamba, 2,4-D) herbicides at the 1× and 2× use rates. Herbicides were applied shortly after planting (PRE) or at the 2 to 4 leaf growth stage (POST). Percent survival was evaluated 5-14 days after application depending on herbicide activity. Sensitivity to atrazine PRE was lower for 49 and 33 accessions out of 115 to atrazine PRE at the 1× and 2× rate, respectively. Most of the accessions (90%) were controlled by isoxaflutole PRE at the 1× rate. Response to S-metolachlor PRE indicated 34% of the Palmer amaranth accessions survived the 1× rate (&gt;60% survival). There were 11 accessions with reduced sensitivity to fomesafen POST; however, these percentages were not different from the 0% survivor group. Glyphosate POST at the 1× rate did not control most accessions (79%). Palmer amaranth response to thifensulfuron-methyl POST varied across the accessions, with only 36 and 28% controlled at the 1× and 2×rate, respectively. All accessions were controlled by 2,4-D, dicamba, or glufosinate POST. Palmer amaranth accessions from this survey exhibited reduced susceptibility to several herbicides commonly used in agronomic crops in South Carolina. Therefore, growers should continue to utilize multiple management tactics to minimize the evolution of herbicide resistance in Palmer amaranth in South Carolina.

Biocontrol potential of Botrytis fabiopsis against the weeds of agricultural fields in the Qing-Tibetan Plateau.

In screening biocontrol strains with broad-spectrum and high-efficiency herbicidal activities, a strain with strong pathogenicity, HY-021, was isolated from the leaves of Rumex acetosa, which was identified as Botrytis fabiopsis based on morphology and molecular biology. The herbicidal activities of the fermentation filtrate of strain HY-021 against nine weeds, including Chenopodium album L., Elsholtzia densa Benth., Malva verticillata L. var. Crispa, Polygonum lapathifolium L., Amaranthus retroflexus L., Avena fatua L., Thlaspi arvense L., Polygonum aviculare L., and Galium spurium L., were determined in vitro and in vivo. The results showed that the pathogenicity of strain HY-021 to the different weeds in vitro was as follows: E. densa > A. retroflexus > P. aviculare > P. lapathifolium > M. verticillata > T. arvense > G. spurium > A. fatua > C. album. Seven days after inoculation with the HY-021 strain, the incidences in nine weeds were in the range of 32.9-87.23%, and the disease index values of the nine weeds were 41.73-94.57%. The pathogenic effects from high to low were A. retroflexus > E. densa > A. fatua > G. spurium > C. album > M. verticillata > T. arvense > P. aviculare > P. lapathifolium. The crop safety test showed that the biocontrol strain HY-021 was safe to V. faba, P. sativum, H. vulgare, and T. aestivum, but had a slight effect on B. napus. Scanning electron microscopy showed that the mycelium of strain HY-021 invaded the tissue through the stomata of C. album leaves, parasitized and reproduced in the tissue, and gradually destroyed the tissue. The results of this study provide a basis for the development and utilization of new and efficient microbial source herbicides.

Yeast Synthesis and Herbicidal Activity Evaluation of Aspterric Acid.

Aspterric acid (AA) is a novel natural product herbicide that targets dihydroxyacid dehydratase in plants. In this study, we introduced two distinct AA biosynthesis-related gene clusters into Saccharomyces cerevisiae and screened the core biosynthetic enzyme, sesquiterpene cyclase, from various fungi. The combination of sesquiterpene cyclase from Aspergillus taichungensis IBT 19404 and two cytochrome P450s from Penicillium brasilianum resulted in the optimal AA synthesis efficiency in yeast, with the highest titer of 33.21 mg/L achieved by optimizing fermentation conditions in shake flasks. Moreover, the herbicidal effects of AA on weed germination and growth were evaluated. Notably, AA strongly inhibited the germination of Amaranthus tricolor, Portulaca oleracea, Bidens pilosa, Lolium perenne, and Leptochloa chinensis. Furthermore, AA could also inhibit the shoot and root growth of weeds with a superior inhibitory effect on roots relative to shoots. Our work not only provides a sustainable method for the biosynthesis of AA in yeast but also paves the way for the application of AA as a preemergence herbicide.

Studies on the synthesis, crystal structures, biological activities and molecular docking of novel natural methylxanthine derivatives containing piperazine moiety.

A series of novel methylxanthine Mannich base derivatives containing substituted piperazine groups were synthesized through Mannich reaction. The structures of these new compounds were confirmed by NMR, HRMS or elemental analyses, and X-ray single crystal diffraction. Bioassay results showed that some of the compounds exhibit favorable fungicidal and insecticidal potentials. Particularly, compounds IIk, IIq, IIs and compounds If, IIk against Physalospora piricola and Rhizoctonia cerealis, respectively, were comparable with Azoxystrobin and Chlorothalonil; compound Ik exhibited higher potency than Triflumuron against Plutella xylostella L., suggesting its potential as a lead compound for further development in insecticidal applications. Despite possessing weak herbicidal activities, the target compounds, especially the methylxanthine S-Mannich base derivatives I displayed remarkable inhibitory activities toward ketol-acid reductoisomerase (KARI); compounds Ib, If, and Ik which had Ki values of 2.41-8.08 µmol/L can be novel potent KARI inhibitors for deeper exploration. The SARs were analyzed in detail. The molecular docking studies on the highly active inhibitors with KARI provided possible binding modes between inhibitor and the target enzyme. The physicochemical parameter predictions indicated that compounds Ik, IIk, IIq and IIs have "druglike structure" features. The research results in this article may bring a new inspiration to the extensive explorations on new methylxanthine derivatives in pesticide area.

Root exudation of glyphosate in Eucalyptus urophylla S.T. Blake

Glyphosate stands out in the eucalyptus management, which makes it essential to know its behavior, its effects on the plant, and possible environmental impacts. This study aimed to identify and quantify the root exudation of glyphosate and aminomethylphosphonic acid (AMPA) by Eucalyptus urophylla with chromatographic and biological methods. The five glyphosate doses were tested (0, 360, 720, 1080 and 1440 g a.e ha−1) on E. urophylla plants. The physiological and intoxication evaluations were performed after herbicide application. Water samples remaining from the pots were used for chemical quantification of root exudation of glyphosate and AMPA in high-performance liquid chromatography. Cucurbita pepo plants were used as bioindicators of glyphosate in the water remaining in the pots after applying herbicide. The increase in glyphosate doses promoted linear growth in E. urophylla intoxication and significantly reduced total dry mass and root production. E. urophylla plants had their photosynthetic, transpiratory, and stomatal conductance rates reduced as the herbicide doses increased. The AMPA root exudation was not detected, but it was possible to identify the presence of glyphosate by bioassay and chemical methods. Root exudation of glyphosate by eucalyptus can result in lesser herbicide action in plant control and cause contamination of deeper soil layers.

Herbicide Formulation Affects Weed Control and Crop Tolerance in Greenhouse Ornamentals

Weed control in container-grown ornamentals can be improved by careful herbicide selection. Four studies were conducted in greenhouses at Oregon State University to improve the understanding of how differences in the mode of action and formulation of herbicides can affect bryophyte control efficacy and crop safety. Granular (G) formulations of pendimethalin and indaziflam were compared with sprayable liquid (L) formulations of pendimethalin, indaziflam, and dimethenamid-p as well as with a nontreated control on four perennial container-grown ornamentals. Indaziflam in the L formulation performed better than that in the G formulations for controlling hairy bittercress up to 20 weeks after the initial treatment. Dimethenamid-p was more effective than indaziflam for liverwort and moss control. Pendimethalin in the G formulation less effectively controlled hairy bittercress than the L formulation did, but it performed better against moss during a second study. The L formulation of indaziflam injured Japanese pachysandra and boxwood and reduced root and shoot growth by 10% to 29%. Dimethenamid-p provided excellent control of the weed species tested and was safe for the crops, indicating its potential use as an alternative to hand-weeding in greenhouses.

Controlled release formulations of encapsulated herbicide enhances herbicide activity as a tool for agro-ecotoxicity

Controlled release formulations of encapsulated herbicide enhances herbicide activity as a tool for agro-ecotoxicity

The herbicidal activity and mechanism of Talaromyces purpureogenus CY-1 metabolites.

Studies have shown that Talaromyces can produce a large number of secondary metabolites in its metabolic process, many of which have good insecticidal, antibacterial, antitumor, antiviral and other biological activities. In order to explore the herbicidal activity and mechanism of Talaromyces purpureogenus CY-1, we determined the inhibitory effect of the fermentation broth of the CY-1 strain on weeds, identified the major active components, and further investigated the herbicidal mechanism. The results showed that CY-1, with IC50 values of 5.40 g/L and 4.39 g/L, respectively, exhibited good herbicidal activity against Xanthium sibiricum and Amaranthus lividus. Spraying CY-1 strain fermentation broth on redroot pigweed resulted in plant protection efficiencies and fresh weight protection efficiencies of 83.7% and 87%, respectively. The active component identified in the broth was 2-(3-hydroxybenzoyloxy) acrylic acid. Treatment of Amaranthus lividus with 2-(3-hydroxybenzoyloxy) acrylic acid resulted in trends of increasing superoxide dismutase activity, peroxidase activity, respiratory rate, cytochrome oxidase activity, and soluble protein content, followed by a decrease. Peroxidase activity, relative conductance and malondialdehyde content gradually increased, while acetyl lactate synthase and glutamine synthetase initially decreased and gradually returned to normal. The soluble sugar content showed a gradual decrease. The findings of the present study indicate that 2-(3-hydroxybenzoyloxy) acrylic acid can induce oxidative stress in plants, damaging plant cell walls, weakening respiratory activity, inhibiting protein synthesis and sugar metabolism, ultimately leading to weed wilting and death. © 2024 Society of Chemical Industry.

Evaluation of herbicidal potential of Siderophores produced by Amycolatopsis lurida strain 407

The urgent need for sustainable agriculture has intensified the search for environmentally friendly alternatives to chemical herbicides. This study investigates the herbicidal potential of siderophores produced by Amycolatopsis lurida strain 407, focusing on its effects on the growth of ryegrass and redroot weeds. Strain 407 exhibited two distinct colony morphologies—red and white—when cultured under varying environmental conditions. The cell-free culture filtrate (CFCF) from both colony types significantly inhibited the growth of ryegrass and redroot. The concentration of siderophore produced in the iron-deficient medium was measured to be 613.4 ppm for 407 red and 388.5 ppm for 407 white, which indicates significant iron chelating activity. This study also showed a direct relationship between the presence of siderophore in plant culture medium and reduced growth. Also, analysis of fractions of the aqueous phase resulting from column chromatography revealed that all fractions from the 407 red reduced ryegrass shoot length by up to 45% and root length by 83–86%, while redroot seedling length decreased by up to 36%. Fractions from 407 white completely inhibited germination or reduced ryegrass root length by up to 94% and redroot seedling length by 52%. Fractions F4 W to F7 W and F2 R to F8 R, which showed iron chelating activity were most effective in reducing plant growth, suggesting that there are metabolites, alone or in company with siderophores, synergistically do herbicidal activity. The innovative application of siderophores as bioherbicide presents a promising environmentally friendly alternative to chemical herbicides.

PfGSTF2 endows resistance to quizalofop-p-ethyl in Polypogon fugax by GSH conjugation.

Populations of Polypogon fugax have developed resistance to many acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. This resistance threats the effectiveness and sustainability of herbicide use. In our previous research, a field P. fugax population exhibited GST-based metabolic resistance to the widely used ACCase-inhibiting herbicide quizalofop-p-ethyl. Here, in this current study, we identified and characterized two GST genes (named as PfGSTF2 and PfGSTF58) that showed higher expression levels in the resistant than the susceptible population. Transgenic rice calli overexpressing PfGSTF2, but not PfGSTF58, became resistant to quizalofop-p-ethyl and haloxyfop-R-methyl. This reflects similar cross-resistance pattern to what was observed in the resistant P. fugax population. Transgenic rice seedlings overexpressing PfGSTF2 also exhibited resistance to quizalofop-p-ethyl. In contrast, CRISPR/Cas9 knockout of the orthologue gene in rice seedlings increased their sensitivity to quizalofop-p-ethyl. LC-MS analysis of in vitro herbicide metabolism by Escherichia coli-expressed recombinant PfGSTF2 revealed that quizalofop (but not haloxyfop) was detoxified at the ether bond, generating the GSH-quizalofop conjugate and a propanoic acid derivative with greatly reduced herbicidal activity. Equally, these two metabolites accumulated at higher levels in the resistant population than the susceptible population. In addition, both recombinant PfGSTF2 and PfGSTF58 can attenuate cytotoxicity by reactive oxygen species (ROS), suggesting a role in plant defence against ROS generated by herbicides. Furthermore, the GST inhibitor (NBD-Cl) reversed resistance in the resistant population, and PfGSTF2 (but not PfGSTF58) responded to NBD-Cl inhibition. All these suggest that PfGSTF2 plays a significant role in the evolution of quizalofop resistance through enhanced herbicide metabolism in P. fugax.

Enhanced removal of chiral emerging contaminants by an electroactive biofilter

50% of pharmaceuticals and 25% of herbicides used worldwide are chiral. Each enantiomer has a unique toxicity and biodegradation profile, affecting differently to organisms. Chirality plays a key role in the behavior of these emerging contaminants (ECs) in terms of their pharmacological or herbicidal activity, but this peculiarity is often overlooked in environmental research. The complexity of chiral ECs is underestimated, as the varying sensitivity of biological systems to enantiomers is rarely considered. Biofilters can promote the activity of specific microbial communities, facilitating the degradation of ECs, due to the greater interaction between water and microorganisms and their compact design. Here, we show that an electroactive biofilter can alter the chirality of drugs and herbicides in wastewater treatment, impacting their removal and toxicity. The electrochemical biofilter (BioeF) removed 80% of pharmaceuticals and 50–75% of herbicides, outperforming the conventional filter (ConF). BioeF also showed greater chiral alterations and lower ecotoxicity. This work provides the first evidence of a relationship between changes in contaminant chirality and detoxification capacity, enhanced by electroactive systems. The increased microbial activity observed in the BioeF suggests that bioelectrochemical systems offer a valuable advance for ECs removal and ecotoxicity reduction, addressing the environmental challenge posed by ECs.

Pseudomonas produce various metabolites displaying herbicide activity against broomrape

Pseudomonads are well-known for their plant growth-promoting properties and biocontrol capabilities against microbial pathogens. Recently, their potential to protect crops from parasitic plants has garnered attention. This study investigates the potential of different Pseudomonas strains to inhibit broomrape growth and to protect host plants against weed infestation. Four Pseudomonas strains, two P. fluorescens JV391D17 and JV391D10, one P. chlororaphis JV395B and one P. ogarae F113 were cultivated using various carbon sources, including fructose, pyruvate, fumarate, and malate, to enhance the diversity of potential Orobanche growth inhibition (OGI)-specialized metabolites produced by Pseudomonas strains. Both global and targeted metabolomic approaches were utilized to identify specific OGI metabolites. Both carbon sources and Pseudomonas genetic diversity significantly influenced the production of OGI metabolites. P. chlororaphis JV395B and P. ogarae F113 produced unique OGI metabolites belonging to different chemical families, such as hydroxyphenazines and phloroglucinol compounds, respectively. Additionally, metabolomic analyses identified an unannotated potential OGI ion, M375T65. This ion was produced by all Pseudomonas strains but was found to be over-accumulated in JV395B, which likely explains its superior OGI activity. Then, greenhouse experiments were performed to evaluate the biocontrol efficacy of selected strains: they showed the efficacy of these strains, particularly JV395B, in reducing broomrape infestation in rapeseed. These findings suggest that certain Pseudomonas strains, through their metabolite production, can offer a sustainable biocontrol strategy against parasitic plants. This biocontrol activity can be optimized by environmental factors, such as carbon amendments. Ultimately, this approach presents a promising alternative to chemical herbicides.

Design, Synthesis of Novel Pyrimidine Derivatives Containing Alkenyl Moieties With Herbicidal Activities

ABSTRACTTo identify lead compounds with potent herbicidal activity, a range of pyrimidine derivatives containing alkenyl groups were designed, synthesized, and characterized using nuclear magnetic resonance (NMR) spectroscopy and high‐resolution mass spectrometry (HRMS). The synthetic pathways for producing these compounds involved substitution reactions, cyclization, hydrolysis, and other processes. The starting materials for each reaction step were readily accessible, facilitating synthesis. The purification of the final product was straightforward, yielding approximately 80%, under mild reaction conditions. Moreover, a pot culture experiment was employed to assess the herbicidal efficacy of the aforementioned compounds. Compounds 6a, 6b, 6h, and 6j demonstrated a significant inhibition against Amaranthus retroflexus, comparable to fomesafen at 150 g a.i./hm2. This suggests that these compounds hold promise as potential lead structures for herbicidal agents. The docking results indicated that the binding energies of compound 6a with protoporphyrinogen oxidase (PPO) were both negative and spontaneous, with numerous interaction active sites. Thus, it is speculated that compound 6a is a PPO inhibitor.

Chemical Synthesis, Herbicidal Activity, Crop Safety, and Molecular Basis of ortho-Fluoroalkoxy Substituted Sulfonylureas as Novel Acetohydroxyacid Synthase Inhibitors.

In the face of increasing resistance to the currently used commercial herbicides and the lack of success in identifying new herbicide targets, alternative herbicides need to be developed to control unwanted monocotyledon grasses in food crops. Here, a panel of 29 novel sulfonylurea-based compounds with ortho-fluoroalkoxy substitutions at the phenyl ring were designed and synthesized. Pot assays demonstrated that two of these compounds, 6d and 6u, have strong herbicidal activities against Echinochloa crus-galli, Eleusine indica, Alopecurus aequalis, and Alopecurus japonicus Steudel at a dosage of 15 g ha-1. Furthermore, these two compounds exhibited <5% inhibition against wheat at a dosage of 30 g ha-1 under post-emergence conditions. 6u also exhibited <5% inhibition against rice at a dosage of 30 g ha-1 under both post-emergence and pre-emergence conditions. A kinetics study demonstrated that 6d and 6u are potent inhibitors of Arabidopsis thaliana acetohydroxyacid synthase (AHAS; EC 2.2.1.6) with potent Ki values of 18 ± 1.1 and 11.9 ± 4.0 nM, respectively. The crystal structure of 6u in complex with A. thaliana (At)AHAS has also been determined at 2.7 Å resolution. These new compounds represent new alternative herbicide choices to protect wheat or rice from invading grasses.

Crystal Structures of Arabidopsis thaliana Acetohydroxyacid Synthase in Complex with the Herbicide Triasulfuron and Two Analogues with Herbicidal Activity in Field Trials.

Triasulfuron is a commercial herbicide of the sulfonylurea family. This compound targets acetohydroxyacid synthase (AHAS, E.C. 2.2.1.6), the first enzyme in the branched chain amino acid biosynthesis pathway. Here, we have determined crystal structures of Arabidopsis thaliana AHAS (AtAHAS) in complex with triasulfuron and two newly designed herbicidal compounds, identified as FMO and CMO, showing that their binding modes are subtly different. Kinetic studies showed all three compounds exhibit varying Ki values, 0.192 ± 0.013 μM for triasulfuron, 0.086 ± 0.013 μM for FMO, and 1.448 ± 0.058 μM for CMO, but all are strong time-dependent accumulative inhibitors of AtAHAS. Apart from triasulfuron being a powerful herbicide with application rates of 10-15 g/ha in wheat fields, CMO and FMO are also herbicidal at 7.5-30 g/ha for barnyard grass. This study emphasizes that accumulative inhibition is an important factor that contributes to herbicidal activity.

Enzymatic Degradation toward Herbicides: The Case of the Sulfonylureas.

Commercial herbicides, particularly sulfonylureas, are used worldwide and pose a significant challenge to environmental sustainability. The efficient degradation of sulfonylurea herbicides is critical. SulE, an esterase isolated from the bacterial strain Hansschlegelia zhihuaiae S113, shows degradation activity toward sulfonylurea herbicides. However, the detailed catalytic mechanism remains vague to a large extent. Herein, we decipher the SulEP44R-catalyzed degradation mechanism of sulfonylurea herbicides using hybrid quantum mechanics and molecular mechanics approaches. Our results show that the degradation of sulfonylureas catalyzed by SulEP44R involves four concerted elementary steps. The rate-determining step has an energy barrier range of 19.7-21.4 kcal·mol-1, consistent with the experimentally determined range of 16.0-18.0 kcal·mol-1. Distortion/interaction analysis demonstrates that active-site amino acids play a vital role in the enzymatic catalytic efficacy. The unique architecture of SulEP44R's active site can serve as an excellent template for designing artificial catalysts. Key structural and charge parameters affecting catalytic activity were systematically screened and identified. Based on the elucidated degradation mechanism, several new herbicides with both high herbicidal activity and biodegradability were developed with the aid of a high-throughput strategy. Our findings may advance the application of sulfonylurea herbicides within the framework of environmental sustainability.