Protoporphyrinogen Oxidase Inhibitors Research Articles

A nonnative Palmer amaranth (Amaranthus palmeri) population in the Republic of South Africa is resistant to herbicides with different sites of action

AbstractPalmer amaranth (Amaranthus palmeriS. Watson) is not native to Africa. Based on the presence and persistence ofA. palmeripopulations, its invasive status in southern Africa is classified as “naturalized.” Globally,A. palmeriis one of the most troublesome weed species in several crops, including soybean [Glycine max(L.) Merr.], maize (Zea maysL.), and cotton (Gossypium hirsutumL.). Certain populations ofA. palmeriin various countries were reported to be resistant to herbicides with different sites of action (SOAs). Two biotypes ofA. palmeriin the United States reportedly each have resistance to herbicides representing five different SOAs, and between them a total of eight different SOAs are involved. Resistance mechanisms in these biotypes involve target-site and/or non–target site resistance. Here we characterize a specificA. palmeripopulation that was found in the Douglas district in South Africa and showed resistance to various herbicide SOAs. Initially, thisA. palmeripopulation was discovered in a glyphosate-tolerant cotton field, where it survived glyphosate treatment. Subsequently, greenhouse experiments were conducted to characterize thisA. palmeripopulation for potential resistance to herbicides of additional SOAs, and molecular analyses were conducted to reveal the mechanisms of herbicide resistance. Results indicated resistance to chlorimuron-ethyl and glyphosate in this population, while <90% control (decreased sensitivity) was observed at the label rate for mesotrione, atrazine, saflufenacil, andS-metolachlor. However, glufosinate, tembotrione, acifluorfen, dicamba, 2,4-D, metribuzin, acetochlor, isoxaflutole, diflufenican, and pyroxasulfone were effective at controlling this population. This profiling of herbicide sensitivity has allowed development of programs to control and potentially minimize the spread of this weed. In addition, molecular analysis ofEPSPSrevealed the role of higher copy number as a mechanism for glyphosate resistance in this population and a Ser-653-Asn target-site mutation likely conferring resistance to the acetolactate synthase–inhibitor chlorimuron-ethyl. No known target-site mutations were identified for the protoporphyrinogen oxidase–inhibitor group.

Lack of human relevance for rat developmental toxicity of flumioxazin is revealed by comparative heme synthesis assay using embryonic erythroid cells derived from human and rat pluripotent stem cells.

Fetal rat anemia from flumioxazin, an N-phenylimide herbicide, is caused by suppression of heme synthesis resulting from inhibition of protoporphyrinogen oxidase (PPO). A series of studies to investigate the effects of flumioxazin have revealed that developmental toxicity is caused in rats but not in rabbits, and the adverse effects are not likely to occur in humans. In this study, as a final weight-of-evidence approach for assessing the human safety of flumioxazin, we compared the toxic potential of inhibition of heme synthesis leading to anemia between human and rat embryonic erythroid cells, which were degenerated as the target of flumioxazin in the rat developmental toxicity. To obtain embryonic erythroid cells, we established respective differentiation methods for embryonic erythroid cells from both human and rat pluripotent stem cells. Derived human and rat embryonic erythroid cells were treated with flumioxazin or dihydroartemisinin (DHA), an anti-malarial drug that causes reduction of embryonic erythroid cells and leads to anemia without species differences. In the human embryonic erythroid cells, DHA inhibited cell proliferation and heme synthesis, whereas there were no effects on heme content or cell proliferation with flumioxazin. In the rat embryonic erythroid cells, however, a dose-related reduction in heme synthesis occurred with treatment of flumioxazin and of DHA. These results confirmed that flumioxazin has no effect on heme synthesis in human embryonic erythroid cells. The present data were in accordance with the results of previous studies and demonstrated that there are no concerns in humans regarding the developmental toxicity of flumioxazin observed in rats.

Stress and use of herbicides in field crops

When herbicides are combined under natural conditions or applied in stress conditions (drought, for instance), the efficiency of their action may decrease which results in considerable yield losses. The reason thereto is that another herbicide or stressor can trigger the adaptation mechanism in weed plants, and they survive, resulting in weed infestation. In particular, it applies to such herbicides as acetyl-CoA-carboxylase inhibitors or so- called graminicides, which are effective only for grass weeds control. The efficiency of this groups of herbi- cides is heavily dependent on the environment and often decreases when combined with herbicides, efficient against dicotyledon weeds. It turns out that this occurs due to the fact their final phytotoxicity is not determined at the level of the site of action (herbicide target) but depends on the stage of herbicide-induced pathogenesis – processes, occurring due to the interaction between the herbicide and its site of action. The stress response of the weeds may make its contribution into herbicide-induced pathogenesis. Plants are known to respond to the action of various abiotic stressors in the form of non-specific stress response and depending on the intensity and duration of the stressor’s action, a plant either adapts or dies. At present there are sufficient data, demonstrating that programmed cell death (PCD) is involved in the herbicide-induced pathogenesis. Reactive oxygen species (ROS) induce PCD in specific classes of herbicides. The participation of ROS and PCD in herbicide-induced pathogenesis allows for targeted effects on the phytotoxic action of herbicides, for instance, via combined application of herbicides with possible PCD inducers and prooxidants. The confirmation of the role of non- specific response in the development of phytotoxic action of herbicides is found in the phenomena of cross- adaptation (activation of antioxidant defense) and cross-synergism (activation of oxidative stress) under the application of herbicides. Based on our own research and literature data, the importance of cross-adaptation and cross-synergism in applying herbicides in drought conditions and to determine the nature of the interac- tion in herbicide complexes is discussed. In particular, the review discusses the reduction of phytotoxicity of the ACCase herbicides due to the phenomenon of cross-adaptation in drought conditions and in combination with herbicides, which are acetolactate synthase inhibitors. The results of investigations were presented about the reduction of antagonism in the mixtures of herbicides, which are ACCase and ALS inhibitors, because of the use of substances with prooxidant properties, as well as the inhibitor of the antioxidant enzyme superoxide dismutase. On the other hand, we analyzed the possibility of increasing the phytotoxic effect of herbicides, ACCase inhibitors, in combination with herbicides with prooxidant properties – inhibitors of electron transport in Photosystem 2 (FS 2) chloroplasts and protoporphyrinogen oxidase (PROTOX) inhibitors. It became the foundation for the elaboration of efficient herbicide compositions for wheat and onion fields. While combining herbicides, the issue of synergism is becoming relevant due to the problem of the spread of target-site resis- tance, since, to prevent this type of resistance, it is necessary to combine herbicides with different mechanisms of phytotoxicity. The presented data demonstrate that the increased activity of antioxidant defense systems, which is the result of a long process of evolutionary adaptation of weeds to the action of abiotic stressors, is an element of non-target-site-based resistance to herbicides. Possible ways to prevent the negative impact of non-specific stress response on the efficiency of herbicides, as well as the prospects of the chemical method of weeds control are discussed.

Characterization and inheritance of dicamba resistance in a multiple-resistant waterhemp (Amaranthus tuberculatus) population from Illinois

AbstractWaterhemp [Amaranthus tuberculatus (Moq.) Sauer] is one of the most troublesome agronomic weeds in the midwestern United States. The rapid evolution and selection of herbicide-resistance traits in A. tuberculatus is a major challenge in managing this species. An A. tuberculatus population, designated CHR, was identified in 2012 in Champaign County, IL, and previously characterized as resistant to herbicides from six site-of-action groups: 2,4-D (Group 4), acetolactate synthase inhibitors (Group 2), protoporphyrinogen oxidase inhibitors (Group 14), 4-hydroxyphenylpyruvate dioxygenase inhibitors (Group 27), photosystem II inhibitors (Group 5), and very-long-chain fatty-acid synthesis inhibitors (Group 15). Recently, ineffective control of CHR was observed in the field after dicamba application. Therefore, this research was initiated to confirm dicamba resistance, quantify the resistance level, and investigate its inheritance in CHR. Multiple field trials were conducted at the CHR location to confirm poor control with dicamba and compare dicamba treatments with other herbicides. Greenhouse trials were conducted to quantify the resistance level in CHR and confirm genetic inheritance of the resistance. In field trials, dicamba did not provide more than 65% control, while glyphosate and glufosinate provided at least 90% control. Multiple accessions were generated from controlled crosses and evaluated in greenhouse trials. Greenhouse dicamba dose–response experiments indicated a resistance level of 5- to 10-fold relative to a sensitive parental line. Dose–response experiments using F1 lines indicated that dicamba resistance was an incompletely dominant trait. Segregation analysis with F2 and backcross populations indicated that dicamba resistance had moderate heritability and was potentially a multigenic trait. Although dicamba resistance was predominantly inherited as a nuclear trait, minor maternal inheritance was not completely ruled out. To our knowledge, CHR is one of the first cases of dicamba resistance in A. tuberculatus. Further studies will focus on elucidating the genes involved in dicamba resistance.

Comparative hepatotoxicity of a herbicide, epyrifenacil, in humans and rodents by comparing the dynamics and kinetics of its causal metabolite.

A new herbicide, epyrifenacil (S-3100), inhibits protoporphyrinogen oxidase (PPO) in plants. Repeated administration of epyrifenacil in laboratory animals led to some toxicological changes related to PPO inhibition, e.g., hepatotoxicity caused by porphyrin accumulation and anemia caused by the inhibition of heme biosynthesis. In vitro studies revealed that an ester-cleaved metabolite, S-3100-CA, is predominant in mammals, exhibits PPO-inhibitory activity, and thus is the cause of epyrifenacil-induced toxicity. To assess the human risk, the effects of species differences on the dynamics (PPO inhibition) and kinetics (liver uptake) of epyrifenacil were evaluated separately. The results of in vitro assays revealed an approximately tenfold weaker inhibition of PPO by S-3100-CA in humans than in rodents and six- to thirteen-fold less hepatic uptake of S-3100-CA in humans than in mice. Finally, it was suggested that humans are less sensitive to the toxicity of epyrifenacil than are rodents, although further mechanistic research is highly anticipated.

Pyrazolotriazines: Biological activities, synthetic strategies and recent developments.

Heterocyclic compounds create an important class of molecules that demonstrates various chemical spaces for the definition of effective medicines. Many N-heterocycles display numerous biological activities. Among condensed heterocycles, pyrazolotriazine derivatives have received the attention of researchers owing to the extensive spectrum of biological activities. The reactivity of identified compounds was similar to the free azoles and triazines. The pyrazolotriazine scaffold exhibited antiasthma, antiinflammatory, anticancer, antithrombogenic activity and showed activity for major depression and pathological anxiety. Pyrazolotriazine derivatives also exhibited antibacterial, anticancer, antimetabolites, antidiabetic, antiamoebic, anticonvulsant, antiproliferative activity, human carbonic anhydrase inhibition, cyclin-dependent kinase 2 inhibition, tyrosinase and urease inhibition, MAO-B inhibition, TTK inhibition, thymidine phosphorylase inhibition, tubulin polymerization inhibition, protoporphyrinogen oxidase inhibition, GABAA agonistic activity, hCRF1 receptor antagonistic activity, and CGRP receptor antagonistic activity. This paper structurally categorized various pyrazolotriazines to isomeric classes into six groups that containing pyrazolo [1,5-d] [1,2,4] triazine, pyrazolo [5,1-c] [1,2,4] triazine, pyrazolo [3,4-e] [1,2,4] triazine, pyrazolo [4,3-e] [1,2,4] triazines, pyrazolo [1,5-a] [1,3,5] triazine, and pyrazolo [3,4-d] [1,2,3] triazine and expressed biological activity, the synthetic procedures for each class of pyrazolotriazines, structure-activity relationship and their mechanism of action. Generally, this review summarily indicated the past and present studies about the discovery of new lead compounds with good biological activity.

Identification of the organic anion transporting polypeptides responsible for the hepatic uptake of the major metabolite of epyrifenacil, S-3100-CA, in mice.

Epyrifenacil is a novel herbicide that acts as an inhibitor of protoporphyrinogen oxidase (PPO) and produces hepatotoxicity in rodents by inhibiting PPO. Our previous research revealed that the causal substance of hepatotoxicity is S‐3100‐CA, a major metabolite of epyrifenacil, and that human hepatocyte uptake of S‐3100‐CA was significantly lower than rodent one, suggesting less relevant to hepatotoxicity in humans. To clarify the species difference in the uptake of S‐3100‐CA, we focused on organic anion transporting polypeptides (OATPs) and carried out an uptake assay using human, rat, and mouse OATP hepatic isoforms‐expressing 293FT cells. As a result, all the examined OATPs were found to contribute to the S‐3100‐CA uptake, suggesting that the species difference was not due to the differences in selectivity toward OATP isoforms. When [14C]epyrifenacil was administered to mice, the liver concentration of S‐3100‐CA was higher in males than in females. Furthermore, when [14C]epyrifenacil was administered with OATP inhibitors, the liver/plasma ratio of S‐3100‐CA was significantly decreased by rifampicin, an Oatp1a1/Oatp1a4 inhibitor in mice, but not by digoxin, an Oatp1a4‐specific inhibitor. This result indicates that Oatp1a1, the predominant transporter in male mice, is the main contributor to the hepatic transport of S‐3100‐CA, and consequently to the gender difference. Moreover, we conclude that the species difference in the hepatic uptake of S‐3100‐CA observed in our previous research is not due to differences in the selectivity toward OATP isoforms but rather to the significantly higher expression of OATPs which mediate uptake of S‐3100‐CA in rodents than in humans.

Response of Brazilian peppertree (Schinus terebinthifolia) and four mangrove species to imazamox and carfentrazone-ethyl herbicides

AbstractMangroves are a critical component of many coastal ecosystems in Florida. Woody species, including Brazilian peppertree (Schinus terebinthifolia Raddi), have invaded thousands of hectares of mangrove habitat. The difficulty associated with ground-based management of invasive plants in mangrove communities has warranted a need to identify selective herbicides that can be applied aerially. Recent work suggests that Florida mangrove species are extremely sensitive to synthetic auxin herbicides; however, other herbicides have yet to be tested for selectivity. Greenhouse studies in 2018 and 2019 evaluated broadcast foliar applications of the acetolactate synthase inhibitor imazamox and protoporphyrinogen oxidase inhibitor carfentrazone-ethyl, both as individual treatments and in combinations, for control of S. terebinthifolia and injury to four non-target mangrove species. Across all posttreatment sample dates and species tested, there were no significant interactions between imazamox applied at 0.28 or 0.56 kg ai ha−1 in combination with carfentrazone-ethyl applied at 0 or 0.1 kg ha−1. Main effects of imazamox applied at 0.56 kg ai ha−1 and carfentrazone-ethyl applied at 0.1 kg ha−1 resulted in 99% and 97% defoliation, respectively, of Schinus terebinthifolia at 180 DAT. However, S. terebinthifolia percent survival was 56% and 44% for the same treatments. Both herbicides severely injured all four mangroves by 90 DAT and resulted in 58% to 100% defoliation across species. At 180 DAT, significant increases in percent cambium kill were also observed for all four species. Across species, mangrove survival varied, but red mangrove (Rhizophora mangle L.) survival was reduced to 6% when imazamox was applied at 0.56 kg ha−1. These results indicate both imazamox and carfentrazone-ethyl exhibit activity on S. terebinthifolia but also injure all four mangroves enough to preclude their use as selective treatments.

Design, synthesis, and herbicidal activity of novel phenoxypyridine derivatives containing natural product coumarin

In recent years, protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors have been widely studied as important agricultural herbicides. Our research focused on the design and synthesis of novel PPO inhibitor herbicides, through linking of a diphenylether pyridine bioisostere structure to substituted coumarins, which aims to enhance environmental and crop safety while retaining high efficacy. A total of 21 compounds were synthesized via acylation reactions and all compounds were characterized using infrared, 1 H NMR, 13 C NMR, and high-resolution mass spectra. The respective configurations of compounds IV-6 and IV-12 were also confirmed using single crystal X-ray diffraction. The bioassay results showed that the title compounds displayed notable herbicidal activity, particularly compound IV-6 which displayed better herbicidal activity in greenhouse and field experiments, crop selectivity and safety for cotton and soybean compared with the commercial herbicide oxyfluorfen. The work revealed that compound IV-6 deserves further attention as a candidate structure for a novel and safe herbicide. © 2021 Society of Chemical Industry.

Phenoxypyridine derivatives containing natural product coumarins with allelopathy as novel and promising proporphyrin IX oxidase-inhibiting herbicides: Design, synthesis and biological activity study

To seek novel and safe protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors with excellent herbicidal activity. A series of novel phenoxypyridine derivatives containing natural product coumarins with allelopathy were designed and synthesized based on bioisosterism and active subunit combination in this research. Compounds W3.1 and W3.4, with the half-maximal inhibitory concentration (IC50) value of 0.02653 mg/L and 0.01937 mg/L, respectively, displayed excellent herbicidal activity in greenhouse. Their herbicidal activity was similar to commercial herbicide oxyfluorfen (IC50 = 0.04943 mg/L). The best field inhibitory effect of compounds W3.1 and W3.4 recorded was at doses of 450 g ai/ha and 300 g ai/ha, respectively. Compound W3.4 had the best herbicidal activity among all the target compounds in this paper. Molecular docking analysis revealed that compounds W3.1 and W3.4 could form a hydrogen bonds with the amino acid AGR-98 and a π-π superposition with the amino acid PHE-398, respectively, which was similar to the oxyfluorfen. The crop selectivity tests results indicated that maize, cotton and soybean showed high tolerance to compound W3.4. Compound W3.4 reduced the Ca and Cb contents of wheat and rice, but had less effect on maize, cotton and soybean. Selectivity of compound W3.4 in maize, cotton and soybean were appeared to be due to reduced absorption of the herbicide compared to wheat and rice. Compound W3.4 deserves further attention as a candidate structure for new herbicides.

Design, synthesis, and molecular simulation studies of N-phenyltetrahydroquinazolinones as protoporphyrinogen IX oxidase inhibitors

Discovering new protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors is a promising direction for agrochemical research. Herein, we reported the discovery and in silico structure-guided optimization of N-phenyltetrahydroquinazolinones 1 and 2 as new PPO inhibitors. Most of the obtained compounds 1 and 2 exhibited significantly enhanced Nicotiana tabacum PPO (NtPPO) inhibitory potency than that of flumioxazin. Promisingly, 1-(tert-butoxy)-1-oxopropan-2-yl 2-chloro-4-fluoro-5-(4-oxo-5,6,7,8-tetrahydroquinazolin-3(4H)-yl)benzoate, 2o, with a Ki value of 4 nM, showed ten folds more enhanced NtPPO-inhibiting potency than flumioxazin. Additionally, compounds 2b and 2i showed a broad spectrum of broadleaf weeds control at 37.5–150 g ai/ha, and selective for wheat at 150 g ai/ha in the post-emergent application. The molecular simulation studies revealed the vital basis between N-phenyltetrahydroquinazolinones and NtPPO. The present work indicated that the N-phenyltetrahydroquinazolinone motif might be a potential scaffold for herbicide discovery.

Herbicide strategies for managing glyphosate-resistant and -susceptible kochia (Bassia scoparia) in spring wheat

Kochia [Bassia scoparia (L.) A.J. Scott] is a summer annual tumbleweed that is tolerant of heat, drought, and salinity and capable of causing large yield losses in spring wheat (Triticum aestivum L). Increased incidence of glyphosate- and acetolactate synthase (ALS) inhibitor-resistant kochia in western Canada warrants investigation of alternative herbicides to manage these biotypes. Herbicides applied pre- or post-emergence in spring wheat were evaluated based on crop tolerance and control of ALS inhibitor-resistant kochia accessions with and without the glyphosate resistance trait in five environments near Lethbridge and Coalhurst, Alberta, from 2013 to 2015. The most effective and consistent treatments for kochia management included sulfentrazone applied pre-emergence and fluroxypyr/bromoxynil/2,4-D or pyrasulfotole/bromoxynil applied post-emergence. All of these treatments resulted in ≥90% visible control in all environments and ≥90% kochia biomass reduction compared with the untreated control in Lethbridge 2014 and 2015. MCPA/dichlorprop-p/mecoprop-p, dicamba/2,4-D/mecoprop-p, and dicamba/fluroxypyr resulted in acceptable control among environments (≥80% visible control in all environments and ≥80% kochia biomass reduction in Lethbridge 2014 and 2015); however, the latter two options caused unacceptable (>10%) wheat visible injury in Coalhurst 2014. Recent confirmations of auxinic herbicide-resistant kochia in western Canada—due, in part, to use of synthetic auxins to manage glyphosate-resistant kochia in small-grain cereals—will limit kochia management options. When implemented with non-chemical tools as part of an integrated weed management program, alternative herbicide modes of action like protoporphyrinogen oxidase inhibitors before and photosystem II or 4-hydroxyphenylpyruvate dioxygenase inhibitor(s) within spring wheat could mitigate selection for multiple herbicide-resistant kochia.

Influence of temperature on the retention, absorption and translocation of fomesafen and imazamox in Euphorbia heterophylla

Climate change will be an additional issue to the challenge to manage herbicide resistant weeds. This work investigated the impact of three temperature regimes (10/5, 20/15 and 30/25 °C) on the efficacy, foliar retention, absorption and translocation of fomesafen, protoporphyrinogen oxidase (PPO) inhibitor, and imazamox, acetolactate synthase (ALS) inhibitor, between two Euphorbia heterophylla populations, one susceptible (S) and one multiple PPO and ALS resistant (R). The R population went from 5 (fomesafen) and 12 (imazamox) times more resistant than the S population at 10/5 °C to more than 100 times to both herbicides at 20/15 and 30/25 °C. Leaf retention of fomesafen was not affected by temperature; however, imazamox retention was less at 10/5 and 20/15 °C than at 30/25 °C, and the R population always retained less imazamox than the S population. 14C-fomesafen absorption was similar between populations, but lower amounts were absorbed at 10/5 °C regardless of the evaluation time. Recovered 14C-imazamox rates decreased in both populations as the evaluation time increased, ranging from 82 to 92% at 6 h after treatment (HAT), and from 47 to 76% at 48 HAT, depending on the temperature regime. The 14C-imazamox losses were greater from 24 HAT in R plants grown at 30/25 °C and in all temperature regimes at 48 HAT. Although both populations translocated large amounts of imazamox, the S population distributed it in the rest of the plant (33%) and roots (15%), while the R population kept it mainly on the treated leaf (24%) or lost ~20% more herbicide than S population at 48 HAT, indicating the need for further studies on root exudation between these populations. Low temperatures reduced resistance levels to fomesafen and imazamox in E. heterophylla, suggesting that temperature influences the expression of the mechanisms that govern this multiple resistance.

Evaluation of peanut tolerance to mid-season applications of PPO-Inhibitor herbicides mixed with different surfactants

Protoporphyrinogen oxidase (PPO) inhibitor herbicides are being increasingly used to control acetolactate synthases (ALS) inhibitor-resistant weeds in peanuts (Arachis hypogaea L.). However, PPO-inhibitor herbicides can injure the crop under certain application conditions, especially under abiotic stress and surfactants may exacerbate this injury. The objectives of this study were to 1) investigate the effect of PPO-inhibitor based treatments on dryland peanut growth and yield when applied at three timings in mid-season, 2) evaluate the interactions of surfactants, chloroacetamide herbicides, and PPO-inhibitors, and 3) assess the level of correlation of normalized difference vegetation index (NDVI) readings to traditional visible injury rating. Field studies were conducted in Henry and Escambia counties in Alabama, U.S. during 2018, and 2019. Up to 55% of visible peanut injury was observed with acifluorfen, lactofen, and carfentrazone-ethyl treatments. In general, the NDVI readings correlated significantly with traditional visible injury ratings. A tank mixture of chloroacetamide herbicides (pyroxasulfone, S-metolachlor, dimethenamid-P) with lactofen did not lead to more injury or yield loss than lactofen applied alone. Yield losses up 27% were observed with carfentrazone-ethyl plus a high surfactant oil concentrate (HSOC) at 75 and 90 days after planting (DAP) as compared to the non-treated check (NTC). Overall, treatments with HSOC and/or carfentrazone-ethyl were more likely to cause significant injury and yield loss than treatments with acifluorfen or lactofen plus nonionic surfactant (NIS). Peanuts are more sensitive to PPO-inhibitor herbicides at 75 DAP. NDVI did provide additional plant health information to subjective injury ratings, however, neither of these measurements are reliable predictors of peanut yield loss.

Elucidation of the species differences of epyrifenacil-induced hepatotoxicity between mice and humans by mass spectrometry imaging analysis in chimeric mice with humanized liver.

Epyrifenacil, one of the protoporphyrinogen oxidase (PPO)-inhibiting herbicides, is hepatotoxic in rodents. Previous in vitro assays detected species differences in both kinetics (active hepatic uptake) and dynamics (PPO inhibitory activity) of S-3100-CA, which is a causal metabolite of the hepatotoxicity, suggesting that humans are less sensitive to the epyrifenacil-induced hepatotoxicity than are rats and mice. To elucidate the species differences in the epyrifenacil-induced hepatotoxicity between mice and humans simultaneously, this study fed epyrifenacil to chimeric mice with humanized liver with low replacement index of human hepatocytes. The distribution of S-3100-CA in the liver and subsequent protoporphyrin IX (PPIX) accumulation, an index of PPO inhibition, were compared between human and host mouse hepatocytes using mass spectrometry imaging (MSI) analysis of chimeric liver. The results showed that S-3100-CA and PPIX were significantly colocalized in regions of the liver slice containing host mouse hepatocytes, and thus it was suggested that epyrifenacil had significantly less effect on human livers than mouse livers because of the species differences in both kinetics and dynamics of S-3100-CA. Moreover, the hepatic uptake assay using cryopreserved primary hepatocytes of rats, mice and humans with inhibitors revealed that S-3100-CA is a substrate of organic anion transporting polypeptides (OATPs). These data corroborate the contribution of OATPs to hepatocellular uptake of S-3100-CA, especially in mice, and subsequent PPIX accumulation by more potent S-3100-CA-induced PPO inhibition in mice. MSI analysis of chimeric mice with humanized liver is a useful technique for elucidating species differences in pharmacokinetics and subsequent changes in toxicological biomarkers.

Design and synthesis of acrylate and acrylamide substituted pyrimidinediones as potential PPO herbicides

PPO herbicides emerge to be widely use in the agricultural field and a focus of research to many scientists due to its environmentally-friendly properties. In lieu with this, this study presents acrylate and acrylamide substituted pyrimidinediones as PPO herbicide candidates. Most synthesized compounds exhibits herbicidal activities against both monocot and dicot weeds, especially, compound 5a which showed non-selective superior activity against the commercialized, Saflufenacil. Compound 5a was further tested for residual effect and showed promising results as shorter period is needed to cultivate the next crops. The synthesized acrylate and acrylamide substituted pyrimidinediones, especially, 5a could potentially be utilized in the development of commercial protoporphyrinogen oxidase inhibitors with further tests and studies.

Different effects of an N-phenylimide herbicide on heme biosynthesis between human and rat erythroid cells

Rat developmental toxicity including embryolethality and teratogenicity (mainly ventricular septal defects and wavy ribs) were produced by S-53482, an N-phenylimide herbicide that inhibits protoporphyrinogen oxidase (PPO) common to chlorophyll and heme biosynthesis. The sequence of key biological events in the mode of action has been elucidated as follows: inhibition of PPO interferes with normal heme synthesis, which causes loss of blood cells leading to fetal anemia, embryolethality and the development of malformations. In this study we investigated whether the rat is a relevant model for the assessment of the human hazard of the herbicide. To study effects on heme biosynthesis, human erythroleukemia, human cord blood, and rat erythroleukemia cells were treated with the herbicide during red cell differentiation. Protoporphyrin IX, a marker of PPO inhibition, and heme were determined. We investigated whether synchronous maturation of primitive erythropoiesis, which can contribute to massive losses of embryonic blood, occurs in rats. The population of primitive erythroblasts was observed on gestational days 11 through 14. Heme production was suppressed in rat erythroid cells. In contrast, heme reduction was not seen in both human erythroid cells when PPO was inhibited. Rats underwent synchronous maturation in primitive erythropoiesis. Our results combined with epidemiological findings that patients with deficient PPO are not anemic led us to conclude that human erythroblasts are resistant to the herbicide. It is suggested that the rat would be an inappropriate model for assessing the developmental toxicity of S-53482 in humans as rats are specifically sensitive to PPO inhibition by the herbicide.

Herbicide mixtures control glyphosate-resistant kochia (Bassia scoparia) in chemical fallow, but their longevity warrants careful stewardship

Glyphosate-resistant kochia [Bassia scoparia (L.) A.J. Scott], the first known glyphosate-resistant weed in western Canada, was confirmed initially in chemical fallow fields located in Warner County, AB, in 2011. Further selection, lack of control, and rampant spread of this biotype contributed to its increased incidence, now present in about 50% of kochia populations sampled in Alberta. In 2014 and 2015, herbicide mixtures were evaluated based on control of glyphosate-resistant and susceptible kochia in chemical fallow fields near Lethbridge and Coalhurst, AB. The most consistent control (≥80% visual control in all environments with ≥80% biomass reduction in 2014) was observed with glyphosate + dicamba (450 + 580 g a.e.·ha−1), glyphosate + dicamba/diflufenzopyr (450 + 150/50 g a.i./a.e.·ha−1), glyphosate + saflufenacil (450 + 50 g a.i./a.e.·ha−1), and glyphosate + carfentrazone + sulfentrazone (450 + 9 + 105 g a.i./a.e.·ha−1). Reduced efficacy was observed for several herbicide mixtures when they were applied to glyphosate-resistant compared with glyphosate-susceptible kochia accessions. Effective modes of action mixed with glyphosate include synthetic auxins (group 4), a combination of a synthetic auxin and an auxin transport inhibitor (group 19), or protoporphyrinogen oxidase inhibitors (group 14). In response to glyphosate-resistant kochia, many farmers in this region shifted their herbicide programs resulting in greater reliance on synthetic auxins; likely contributing to the recent discovery of auxinic herbicide-resistant kochia biotypes in Alberta in 2017. Careful herbicide stewardship is warranted to mitigate further selection of multiple herbicide-resistant kochia, suggesting an important role for integrated weed management.

Managing herbicide resistance in China

AbstractSince its initial introduction in the late 1950s, chemical control has dominated weed management practices in China. Not surprisingly, the development of herbicide resistance has become the biggest threat to long-term, sustainable weed management in China. Given that China has followed the same laissez-faire approach toward resistance management that has been practiced in developed countries such as the United States, herbicide resistance has evolved rapidly and increased steadily over the years. Previously, we carried out a systematic review to quantitatively assess herbicide-resistance issues in China. In this review, our main objective is to focus on mechanistic studies and management practices to document the (1) history of herbicide application in China; (2) resistance mechanisms governing the eight most resistance-prone herbicide groups, including acetolactate synthase inhibitors, acetyl-CoA carboxylase inhibitors, synthetic auxin herbicides, 5-enolpyruvylshikimate-3-phosphate synthase inhibitors, protoporphyrinogen oxidase inhibitors, photosystem I electron diverters, photosystem II inhibitors, and long-chain fatty-acid inhibitors; and (3) herbicide-resistance management strategies commonly used in China, including chemical, cultural, biological, physical, and integrated approaches. At the end, perspectives and future research are discussed to address the pressing need for the development of integrated herbicide-resistance management in China.

Susceptibility of Palmer amaranth (Amaranthus palmeri) to herbicides in accessions collected from the North Carolina Coastal Plain

AbstractPalmer amaranth (Amaranthus palmeri S. Watson) populations resistant to acetolactate synthase (ALS)-inhibiting herbicides and glyphosate are fairly common throughout the state of North Carolina (NC). This has led farm managers to rely more heavily on herbicides with other sites of action (SOA) for A. palmeri control, especially protoporphyrinogen oxidase and glutamine synthetase inhibitors. In the fall of 2016, seeds from A. palmeri populations were collected from the NC Coastal Plain, the state’s most prominent agricultural region. In separate experiments, plants with 2 to 4 leaves from the 110 populations were treated with field use rates of glyphosate, glufosinate-ammonium, fomesafen, mesotrione, or thifensulfuron-methyl. Percent visible control and survival were evaluated 3 wk after treatment. Survival frequencies were highest following glyphosate (99%) or thifensulfuron-methyl (96%) treatment. Known mutations conferring resistance to ALS inhibitors were found in populations surviving thifensulfuron-methyl application (Ala-122-Ser, Pro-197-Ser, Trp-574-Leu, and/or Ser-653-Asn), in addition to a new mutation (Ala-282-Asp) that requires further investigation. Forty-two populations had survivors after mesotrione application, with one population having 17% survival. Four populations survived fomesafen treatment, while none survived glufosinate. Dose–response studies showed an increase in fomesafen needed to kill 50% of two populations (LD50); however, these rates were far below the field use rate (less than 5 g ha−1). In two populations following mesotrione dose–response studies, a 2.4- to 3.3-fold increase was noted, with LD90 values approaching the field use rate (72.8 and 89.8 g ha−1). Screening of the progeny of individuals surviving mesotrione confirmed the presence of resistance alleles, as there were a higher number of survivors at the 1X rate compared with the parent population, confirming resistance to mesotrione. These data suggest A. palmeri resistant to chemistries other than glyphosate and thifensulfuron-methyl are present in NC, which highlights the need for weed management approaches to mitigate the evolution and spread of herbicide-resistant populations.