Herbicide-resistant HPPD variants identified via directed evolution.

Herbicides play a crucial role in boosting crop yields, yet the emergence of herbicide-resistant weeds and the susceptibility of crops to herbicides have posed significant challenges to their efficacy. ß-triketone herbicides specifically target the enzyme 4-Hydroxyphenylpyruvate dioxygenase (HPPD) essential for plant growth. Remarkably, few resistant weeds have been identified against these herbicides. In this study, we aimed to identify mutations within the cotton HPPD gene that confer resistance to mesotrione, a widely used triketone herbicide. Through the establishment of a high-throughput mutant screening system in E. coli, we identified four single nucleotide changes leading to amino acid substitutions in HPPD, resulting in mesotrione resistance while preserving native enzymatic activity. Various combinations of these mutations displayed synergistic effects on herbicide resistance. Additionally, the HPPD variants were able to complement the Arabidopsis athppd mutant, indicating their retention of sufficient native activity crucial for plant growth and development. Expression of these cotton HPPD variants in Arabidopsis resulted in heightened herbicide resistance. These findings offer critical insights into the target amino acids of HPPD for gene editing, paving the way for the development of herbicide-resistant cotton in the future.

4-Hydroxyphenylpyruvate Dioxygenase Inhibitors: From Molecular Design to Synthesis.

Weed resistance is a critical issue in crop production. Among the known herbicides, 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors are crucial for addressing weed resistance. HPPD inhibitors constitute a pivotal aspect of contemporary crop protection strategies. The advantages of these herbicides are their broad weed spectrum, flexible application, and excellent compatibility with other herbicides. They also exhibit satisfactory crop selectivity and low toxicity and are environmentally friendly. An increasing number of new HPPD inhibitors have been designed by combining computer-aided drug design with conventional design approaches. Herein, the molecular design and structural features of innovative HPPD inhibitors are reviewed to guide the development of new HPPD inhibitors possessing an enhanced biological efficacy.

Molecular and Evolution In Silico Studies Unlock the h4-HPPD C-Terminal Tail Gating Mechanism.

The enzyme 4-hydroxyphenylpyruvate dioxygenase (4-HPPD) is involved in the catabolism of the amino acid tyrosine in organisms such as bacteria, plants, and animals. It catalyzes the conversion of 4-hydroxyphenylpyruvate to a homogenisate in the presence of molecular oxygen and Fe(II) as a cofactor. This enzyme represents a key step in the biosynthesis of important compounds, and its activity deficiency leads to severe, rare autosomal recessive disorders, like tyrosinemia type III and hawkinsinuria, for which no cure is currently available. The 4-HPPD C-terminal tail plays a crucial role in the enzyme catalysis/gating mechanism, ensuring the integrity of the active site for catalysis through fine regulation of the C-terminal tail conformation. However, despite growing interest in the 4-HPPD catalytic mechanism and structure, the gating mechanism remains unclear. Furthermore, the absence of the whole 3D structure makes the bioinformatic approach the only possible study to define the enzyme structure/molecular mechanism. Here, wild-type 4-HPPD and its mutants were deeply dissected by applying a comprehensive bioinformatics/evolution study, and we showed for the first time the entire molecular mechanism and regulation of the enzyme gating process, proposing the full-length 3D structure of human 4-HPPD and two novel key residues involved in the 4-HPPD C-terminal tail conformational change.

Physiological Basis for the Mechanism of Selectivity of Tripyrasulfone between Rice (Oryza sativa) and Barnyard Grass (Echinochloa crus-galli).

Tripyrasulfone is currently the only HPPD-inhibiting herbicide that possesses outstanding selectivity even for direct-seeded rice (Oryza sativa) when applied POST to control grass weeds; however, the underlying mechanisms remain unclear. In this study, the inhibitory effects of the real active HDT of tripyrasulfone on recombinant 4-hydroxyphenylpyruvate dioxygenase (HPPDs) from rice and barnyard grass (Echinochloa crus-galli) were similar, with consistent structural interactions and similar binding energies predicted by molecular docking. However, the HPPD expression level in rice was significantly greater than that in barnyard grass after tripyrasulfone treatment. Tripyrasulfone was rapidly taken up and hydrolyzed into HDT, which was similarly distributed within the whole plants of rice and barnyard grass at 24 h after treatment. Compared with barnyard grass, rice has more uniform epicuticular wax in the cuticle of its leaves, absorbing less tripyrasulfone and metabolizing much more tripyrasulfone. Overall, to a greater extent, the different sensitivities to tripyrasulfone between barnyard grass and rice resulted from metabolic variations.

Physiological effects of maize stressed by HPPD inhibitor herbicides via multi-spectral technology and two-dimensional correlation spectrum technology.

Understanding the physiological effects of herbicides on crops is crucial for crop production and environmental management. The effects of 4-hydroxyphenylpyruvate dioxygenase inhibitor (HPPDi) herbicides at different concentrations on chlorophyll content in maize leaves, fresh weight of roots, stems and leaves, and fluorescence substances and functional groups in root exudates (REs) were studied by UV-Vis absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR) and two-dimensional correlation analysis (2D-COS). The results showed that 5 mg/L and 10 mg/L HPPDi herbicides inhibited the synthesis of chlorophyll in maize leaves. The weight of roots, stems and leaves of maize after application was lighter than that of the control group. HPPDi herbicides affected the early growth of maize seedlings, and the effect was most obvious at high concentration. Synchronous fluorescence spectrum and three-dimensional (3D) fluorescence spectrum revealed that the fluorescence intensity of protein, fulvic acid and humic acid in maize REs changed prominently. With the increase of HPPDi herbicides concentration, the fluorescence intensity decreased gradually. Through FTIR and 2D-COS, functional groups such as C-H, CO, Cl, NO3-, C-O and O-H were found to participate in the interaction between HPPDi herbicides and maize REs as binding sites. C-O, C-Cl and C-C have the strongest binding ability, while CC and CO of aromatic rings, quinones or ketones first take part in the binding between HPPDi herbicides and maize REs. The results can provide a theoretical basis for evaluating the safety of HPPDi herbicides on maize and a method for discovering the effects of pesticides on environmental media and plant physiological effects.

Integrated Virtual Screening and Validation toward Potential HPPD Inhibition Herbicide.

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) is one of the most widely studied herbicide targets and has gained significant attention. To identify potential effective HPPD inhibitors, a rational multistep virtual screening workflow was built, which included CBP models (based on the receptor-ligand interactions in the crystal complex), Hypogen models with activity prediction ability (according to the derivation of structure-activity relationships from a set of molecules with reported activity values), and a consensus docking procedure (consisting of LibDock, Glide, and CDOCKER). About 1 million molecules containing diketone or ß-keto-enol substructures were filtered by Lipinski's rules, CBP model, and Hypogen model. A total of 12 compounds with similar docking postures were generated by consensus docking. Eventually, four molecules were screened based on the specific binding pattern and affinity of the HPPD inhibitor. The biological evaluation in vivo displayed that compounds III-1 and III-2 exhibited comparable herbicidal activity to isoxaflutole and possessed superior safety on various crops (wheat, rice, sorghum, and maize). The ADMET prediction (absorption, distribution, metabolism, excretion, and toxicity) showed that compound III possessed relatively good toxicological results. This work provides a theoretical basis and valuable reference for the virtual screening and molecular design of novel HPPD inhibition herbicides.

Crystal structure of HPPD inhibitor sensitive protein from Oryza sativa.

4-hydroxyphenylpyruvate dioxygenase (HPPD) Inhibitor Sensitive 1 (HIS1) is an endogenous gene of rice, conferring broad-spectrum resistance to ß-triketone herbicides. Similar genes, known as HIS1-like genes (HSLs), exhibit analogous functions and can complement the herbicide-resistant characteristics endowed by HIS1. The identification of HIS1 and HSLs represents a valuable asset, as the intentional pairing of herbicides with resistance genes emerges as an effective strategy for crop breeding. Encoded by HIS1 is a Fe(II)/2-oxoglutarate-dependent oxygenase responsible for detoxifying ß-triketone herbicides through hydroxylation. However, the precise structure supporting this function remains unclear. This work, which determined the crystal structure of HIS1, reveals a conserved core motif of Fe(II)/2-oxoglutarate-dependent oxygenase and pinpoints the crucial residue dictating substrate preference between HIS1 and HSL.

A novel Zn2+-coordination fluorescence probe for sensing HPPD inhibitors and its application in environmental media and biological imaging.

Mesotrione, topramezone, tembotrione, and sulcotrione are four types of 4-hydroxyphenylpyruvate dioxidase (HPPD) inhibitor herbicides that are extensively employed in agricultural practices, but their usage also leads to environmental pollution and poses risks to human health. A probe (E)-1-((2-(pyridin-2-yl) hydrazineylidene) methyl) naphthalen-2-ol (CHMN) based on chelation enhancement (CHEF) effect synthesized. CHMN was first chelated with Zn2+ to form a probe system with green, which can be further used to detect mesotrione, topramezone, tembotrione and sulcotrione in complicated environment. CHMN-Zn2+ detection of four pesticides was accurate, with an excellent linear relationship between 0 and 100 µM. The detection limits were LODmesotrione = 7.79 µM, LODtopramezone = 1.91 µM, LODtembotrione = 1.38 µM and LODsulcotrione = 2.43 µM. The detection time is 1 min, and it is successfully applied in real water sample and bioimaging. This work can provide a novel method for studying the migration and behavior of environmental pollutants.

Longitudinal associations between psychedelic use and unusual visual experiences in the United States and the United Kingdom.

BACKGROUND: Whereas findings from case reports and cross-sectional studies suggest that naturalistic psychedelic use may be associated with unusual visual experiences that occur after the acute pharmacological effects have subsided, such findings need to be replicated in longitudinal studies to better understand potential cause-and-effect relationships. AIMS: To investigate longitudinal associations between naturalistic psychedelic use and unusual visual experiences. METHODS: Using a longitudinal observational research design with samples representative of the US and UK adult populations with regard to sex, age, and ethnicity (N = 9732), we investigated the relationship between psychedelic use during the 2-month study period and changes in past-week unusual visual experiences. RESULTS: The follow-up survey was completed by 79% of respondents (n = 7667), with 100 respondents reporting psychedelic use during the 2-month study period (1.3% of those who responded at follow-up). In covariate-adjusted regression models, the results showed that, as hypothesized, psychedelic use during the 2-month study period was associated with greater increases in unusual visual experiences. Notably, there was an interaction between lifetime psychedelic use and psychedelic use during the study period on unusual visual experiences such that those who used psychedelics for the first time reported greater increases in unusual visual experiences. CONCLUSIONS: Psychedelic use may elicit unusual visual experiences that occur after the acute pharmacological effects have subsided, especially among those who have not used psychedelics previously. Future longitudinal studies are warranted to further elucidate these relationships.

Design, Synthesis, and Bioactivity of Novel 2-(Arylformyl)cyclohexane-1,3-dione Derivatives as HPPD Inhibitors.

4-Hydroxyphenylpyruvate dioxygenase inhibitors (Echinochloa crus-galli 1.13.11.27, HPPD) have gained significant popularity as one of the best-selling herbicides worldwide. To identify highly effective HPPD inhibitors, a rational design approach utilizing bioisosterism was employed to create a series of 2-(arylformyl)cyclohexane-1,3-dione derivatives. A total of 29 novel compounds were synthesized and characterized through various techniques, including IR, 1H NMR, 13C NMR, and HRMS. Evaluation of their inhibitory activity against Arabidopsis thaliana HPPD (AtHPPD) revealed that certain derivatives exhibited superior potency compared to mesotrione (IC50 = 0.204 µM). Initial herbicidal activity tests demonstrated that compounds 27 and 28 were comparable to mesotrione in terms of weed control and crop safety, with compound 28 exhibiting enhanced safety in canola crops. Molecular docking analyses indicated that the quinoline rings of compounds 27 and 28 formed more stable π-π interactions with the amino acid residues Phe-360 and Phe-403 in the active cavity of AtHPPD, surpassing the benzene ring of mesotrione. Molecular dynamics simulations and molecular structure comparisons confirmed the robust binding capabilities of compounds 27 and 28 to AtHPPD. This study provides a valuable reference for the development of novel triketone herbicide structures, serving as a blueprint for future advancements in this field.

Association of Hallucinogen Persisting Perception Disorder with Trait Neuroticism and Mental Health Symptoms.

Hallucinogen Persisting Perception Disorder (HPPD) is considered rare in hallucinogen users although there are conflicting reports about its incidence and prevalence. HPPD may be more common in those with trait neuroticism. In this study, we invited hallucinogen and other drug users to complete an online questionnaire about their use of hallucinogens, their experience of HPPD symptoms, and their trait neuroticism and mental health symptoms. We received 802 responses with 415 of these containing adequate data for further analysis. 39.7% of responders reported symptoms corresponding to Type I HPPD, and 4.3% reported symptoms corresponding to Type II HPPD. We found no significant difference between neuroticism scores for participants with or without HPPD. Individuals with Type II HPPD were more likely to report mental health symptoms including anxiety, obsessional thoughts, paranoia, hypochondria and panic attacks (p < .05). We also found that individuals with Type II HPPD were more likely to report the use of 25I-NBOMe, dextromethorphan, nitrous oxide and benzodiazepines (p < .05). 47.3% of participants had never tested their drugs, making the attribution of HPPD severity to specific drugs difficult. Further work into the development of HPPD is required, particularly with the rise of hallucinogens as potential treatments for depression and other mental illnesses.

Transcriptomic analysis of wheat reveals possible resistance mechanism mediated by Yr10 to stripe rust.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a catastrophic disease that threatens global wheat yield. Yr10 is a race-specific all-stage disease resistance gene in wheat. However, the resistance mechanism of Yr10 is poorly characterized. Therefore, to elucidate the potential molecular mechanism mediated by Yr10, transcriptomic sequencing was performed at 0, 18, and 48 h post-inoculation (hpi) of compatible wheat Avocet S (AvS) and incompatible near-isogenic line (NIL) AvS + Yr10 inoculated with Pst race CYR32. Respectively, 227, 208, and 4050 differentially expressed genes (DEGs) were identified at 0, 18, and 48 hpi between incompatible and compatible interaction. The response of Yr10 to stripe rust involved various processes and activities, as indicated by the results of Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Specifically, the response included photosynthesis, defense response to fungus, metabolic processes related to salicylic acid (SA) and jasmonic acid (JA), and activities related to reactive oxygen species (ROS). Ten candidate genes were selected for qRT-PCR verification and the results showed that the transcriptomic data was reliable. Through the functional analysis of candidate genes by the virus-induced gene silencing (VIGS) system, it was found that the gene TaHPPD (4-hydroxyphenylpyruvate dioxygenase) negatively regulated the resistance of wheat to stripe rust by affecting SA signaling, pathogenesis-related (PR) gene expression, and ROS clearance. Our study provides insight into Yr10-mediated resistance in wheat.

Psychedelic use and psychiatric risks.

RATIONALE: Research on psychedelics has recently shown promising results in the treatment of various psychiatric disorders, but relatively little remains known about the psychiatric risks associated with naturalistic use of psychedelics. OBJECTIVE: The objective of the current study was to investigate associations between naturalistic psychedelic use and psychiatric risks. METHODS: Using a sample representative of the US adult population with regard to sex, age, and ethnicity (N=2822), this study investigated associations between lifetime naturalistic psychedelic use, lifetime unusual visual experiences, and past 2-week psychotic symptoms. RESULTS: Among respondents who reported lifetime psychedelic use (n=613), 1.3% reported having been told by a doctor or other medical professional that they had hallucinogen persisting perception disorder. In covariate-adjusted linear regression models, lifetime psychedelic use was associated with more unusual visual experiences at any point across the lifetime, but no association was observed between lifetime psychedelic use and past 2-week psychotic symptoms. There was an interaction between lifetime psychedelic use and family (but not personal) history of psychotic or bipolar disorders on past 2-week psychotic symptoms such that psychotic symptoms were highest among respondents who reported lifetime psychedelic use and a family history of psychotic or bipolar disorders and lowest among those who reported lifetime psychedelic use and no family history of psychotic or bipolar disorders. CONCLUSIONS: Although the results in this study should be interpreted with caution, the findings suggest that lifetime naturalistic use of psychedelics might be associated with more unusual visual experiences across the lifetime, as well as more psychotic symptoms in the past 2 weeks for individuals with a family history of psychotic or bipolar disorders and the reverse for those without such a family history. Future research should distinguish between different psychotic and bipolar disorders and should also utilize other research designs (e.g., longitudinal) and variables (e.g., polygenic risk scores) to better understand potential cause-and-effect relationships.

First Report on Resistance to HPPD Herbicides Mediated by Nontarget-Site Mechanisms in the Grass Leptochloa chinensis.

The emergence of 4-hydroxyphenylpyruvate dioxygenase (HPPD) herbicides as efficacious target-site herbicides has been noteworthy. In recent years, only four species of broadleaf weeds have developed resistance due to the long-term widespread use of HPPD herbicides. This study represents the first reported instance of a grass weed exhibiting resistance to HPPD inhibitors. We identified a new HPPD-resistant Chinese sprangletop [Leptochloa chinensis (L.) Nees] population (R population). At the recommended dose of tripyrasulfone, the inhibition rate of the R population was only half that of the sensitive population (S). The mechanism underlying resistance does not involve target-site resistance triggered by amino acid mutations or depend on disparities within the HPPD INHIBITOR SENSITIVE 1 (HIS1) gene. The impetus for resistance appears to be interlinked with the metabolic activities of cytochrome P450 monooxygenase (P450) and glutathione S-transferase (GST) family genes. Following RNA sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) validation, the study suggests that five P450 genes, CYP71C1, CYP74A2, CYP72A1, CYP84A1, and CYP714C2, alongside a single GST gene GSTF1, may be implicated in the process of metabolic detoxification.

Improving the Herbicide Resistance of Rice 4-Hydroxyphenylpyruvate Dioxygenase by DNA Shuffling Basis-Directed Evolution.

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an ideal target for herbicide resistance genetic engineering. In this study, a mutant MFRR-2 with mesotrione resistance was screened from an Oryza sativa HPPD and mutant-Zea mays HPPD DNA shuffling library. The enzyme properties showed that although the stability of the mutant decreased in vitro, the enzyme activity of MFRR-2 at the optimum temperature of 25 °C was still equivalent to that of OsHPPD. Under 50 µM mesotrione treatment, MFRR-2 enzyme activity remained at approximately 90%, while the enzyme activity of OsHPPD decreased by approximately 50%. Surprisingly, Fe2+ was found to have an inhibitory effect on the enzyme activity. Then, the transgenic rice of the MFRR-2 gene showed approximately 1.5 times mesotrione resistance compared to OsHPPD transgenic rice. In conclusion, this study has conducted a beneficial exploration on the use of DNA shuffling for HPPD-directed evolution, and the mutant has potential application value for herbicide resistance genetic engineering.

Design, synthesis and biological activity of novel triketone herbicides containing natural product fragments.

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) belongs to the non-heme Fe2+ - containing enzyme family and is an important enzyme in tyrosine decomposition. HPPD is crucial to the discovery of novel bleaching herbicides. To develop novel HPPD inhibitor herbicides containing the ß-triketone motif, a series of 4-hydroxyl-3-(substituted aryl)-pyran-2-one derivatives were designed using the active fragment splicing method. The title compounds were synthesized and characterized through infrared spectroscopy (IR), 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR), and high-resolution mass spectrometry (HRMS). The X-ray diffraction method determined the single crystal structure of I-17. Preliminary bioassay data revealed that several novel compounds, especially I-12 and II-3, showed excellent herbicidal activity against broadleaf and monocotyledonous weeds at a dose of 150 g ai/ha. The results of crop selectivity and carotenoids determination indicated that compound I-12 is more suitable for wheat and cotton fields than mesotrione. Additionally, compound II-3 is safer for soybeans and peanuts than mesotrione. The inhibitory activity of Arabidopsis thaliana HPPD (AtHPPD) verified that compound II-3 showed the most activity with an IC50 value of 0.248 µM, which was superior to that of mesotrione (0.283 µM) in vitro. The binding mode of compound II-3 and AtHPPD was confirmed through molecular docking and molecular dynamics simulations. This study provides insights into the future development of natural and efficient herbicides.

Defining the toxicological profile of 4-hydroxyphenylpyruvate dioxygenase-directed herbicides to Aedes aegypti and Amblyomma americanum.

Inhibitors targeting the 4-hydroxyphenyl pyruvate dioxygenase (HPPD) enzyme are well established herbicides and HPPD is also a primary enzyme within the tyrosine metabolism pathway in hematophagous arthropods, which is an essential metaboilic pathway post-blood feeding to prevent tyrosine-mediated toxicity. The objective of this study was to characterize the toxicity of triketone, pyrazole, pyrazolone, isoxazole, and triazole herbicides that inhibit HPPD to blood-fed mosquitoes and ticks. Topical exposure of nitisinone to blood-fed Aedes aegypti yielded high toxicity with an LD50 of 3.81 ng/insect (95% CI: 3.09 to 4.67 ng; Hillslope: 0.97, r2: 0.99), yet was non-toxic to non-blood fed (NBF) mosquitoes. The rank order of toxicity was nitisinone > tembotrione > pyrazoxyfen > tebuconazole > mesotrione against blood-fed Ae. Aegypti, but nitisinone was approximately 30-fold more toxic than other chemicals tested. We also assessed the toxicity of HPPD-inhibiting herbicides to the lone star tick, Amblyomma americanum and similarly, nitisinone was toxic to Am. americanum with a lethal time to kill 50% of subjects (LT50) of 23 h at 10 µM. Knockdown of the gene encoding the HPPD enzyme was performed through RNA-interference led to significant mortality after blood feeding in both, Ae. aegypti and Am. americanum. Lastly, a fluorescence assay was developed to determine relative quantities of L-tyrosine in Ae. aegypti and Am. americanum treated with HPPD inhibitors. L-tyrosine levels correlated with toxicity with nitisinone exposure leading to increased tyrosine concentrations post-blood feeding. Taken together, these data support previous work suggesting HPPD-inhibitors represent a novel mode of toxicity to mosquitoes and ticks and may represent base scaffolds for development of novel insecticides specific for hematophagous arthropods.

Method validation and dissipation kinetics of the novel HPPD-inhibiting herbicide cypyrafluone in winter wheat using QuEChERS method coupled with UPLC-MS/MS.

Cypyrafluone, a novel hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide, can successfully control a wide species of grass and broadleaf weed in wheat fields. However, the dissipation behaviors and terminal residues of cypyrafluone in wheat fields remain unclear. Here, a simple, accurate, and dependable approach for the analysis of cypyrafluone in soil, wheat plant, and grain was constructed utilizing an adapted QuEChERS extraction combined with UPLC-MS/MS. For accurate quantification, matrix-matched calibrations with high linearity (R2 >0.99) were employed to eliminate matrix interference. The method possessed high accuracy with recoveries in the range of 85.5%- 100.6% and precision with relative standard deviations < 14.3%, as well as high sensitivity with limits of quantifications of 0.001 mg kg-1 in the three matrixes. The dissipation kinetics and terminal residues of cypyrafluone were determined at two separate locations with different climates, soil types and cropping systems in 2018. The half-lives of cypyrafluone in soil and wheat plant were 1.47-1.55 d and 1.00-1.03 d, respectively. At harvest, the terminal residue values of cypyrafluone detected in wheat plants were 0-0.0025 mg kg-1 and 0.0044-0.0057 mg kg-1 at the recommended dose and 1.5 times of the recommended dose, respectively, and 0.0049 mg kg-1 of this herbicide was detected in grain at 1.5 times of the recommended dose, which was below the maximum residue limit (MRL). Finally, the risk quotient for cypyrafluone ranged from 0.33% to 0.81% (<1) for different age groups in China, indicating that the impact of residues from the cypyrafluone application on wheat was acceptable. These findings above will offer scientific guidelines for cypyrafluone application in the wheat field ecosystem.

Cypyrafluone, a 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor to Control Weed in Wheat Fields.

As a bleaching herbicide, cypyrafluone was applied postemergence in wheat fields for annual weed control; especially, this herbicide possesses high efficacy against cool-season grass weed species such as Alopecurus aequalis and Alopecurus japonicus. In this study, the target of action of cypyrafluone on 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibition was confirmed. This herbicide caused severe foliar whitening symptoms at 5-7 days after treatment (DAT) and death of the whole plant within 10 DAT. Significant increases in phytoene content and significant decreases in kinds of carotenoid and chlorophyll pigments were observed. The content of chlorophyll pigments in cypyrafluone-treated Spirodela polyrhiza decreased upon the addition of homogentisic acid (HGA), which indicated that cypyrafluone prevents the HGA production, possibly by inhibiting the catalytic activity of 4-HPPD. Indeed, cypyrafluone strongly inhibited the catalytic activity of Arabidopsis thaliana HPPD produced by Escherichia coli, which was approximately 2 times less effective than mesotrione. In addition, overexpression of Oryza sativa HPPD in rice and A. thaliana both conferred a high tolerance level to cypyrafluone on them. Molecular docking found that cypyrafluone bonded well to the active site of the HPPD and formed a bidentate coordination interaction with the Fe2+ atom, with distances of 2.6 and 2.7 Å between oxygen atoms and the Fe2+ atom and a binding energy of -8.0 kcal mol-1.

Non-destructive estimation of weed response to bleaching herbicides by Raman spectroscopy.

The aim of our study was to evaluate the use of Raman spectroscopy for pre-diagnostic estimation of weed response to bleaching herbicides. Model plants were Chenopodium album and Abutilon theophrasti treated with mesotrione (120 g a.i. ha-1). Raman single-point measurements were taken 1, 2, 3, and 7 days after herbicide application from different points on the leaves. Principal component analysis (PCA) was carried out on data normalized by the highest intensity band at 1522 cm-1 and using spectral region from 950 to 1650 cm-1 comprising mainly contributions of carotenoids. The carotenoids by intensive band at ∼1522 cm-1 and bands with lower intensity at ∼1155 and 1007 cm-1 in treated plants were confirmed. According to PC1 (the first principal component) and PC2 (the second principal component), the highest intensity bands responsible for treatment differentiation in C. album could be assigned to chlorophyll, lignin, and carotenes. According to PC1 in A. theophrasti leaves the treatment differences could be observed 7 days after mesotrione treatment and PC2 gave a clear separation between all control and treated leaf samples. Raman spectroscopy may be a good complement to invasive analytical methods, in assessing the plant abiotic stress induced by bleaching herbicides.