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Evans, Cody M., Seth A. Strom, Dean E. Riechers, Adam S. Davis, Patrick J. Tranel y Aaron G. Hager. "Characterization of a waterhemp (Amaranthus tuberculatus) population from Illinois resistant to herbicides from five site-of-action groups". Weed Technology 33, n.º 03 (23 de mayo de 2019): 400–410. http://dx.doi.org/10.1017/wet.2019.19.
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AbstractExperiments were initiated to characterize a waterhemp population (CHR) discovered in a central Illinois corn field after it was not controlled by the 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor topramezone. Field experiments conducted during 2014–2015 indicated that acetolactate synthase (ALS)-, protoporphyrinogen oxidase (PPO)-, photosystem II (PSII)-, and HPPD-inhibiting herbicides and the synthetic auxin 2,4-D did not control the CHR population. Laboratory experiments confirmed target site–based resistance mechanisms to ALS- and PPO-inhibiting herbicides. Herbicide doses required to reduce dry biomass 50% (GR50) were determined in greenhouse dose–response experiments, and indicated 16-fold resistance to the HPPD inhibitor mesotrione, 9.5-fold resistance to the synthetic auxin 2,4-D, and 252-fold resistance to the PSII inhibitor atrazine. Complementary results from field, laboratory, and greenhouse investigations indicate that the CHR population has evolved resistance to herbicides from five sites of action (SOAs): ALS-, PPO-, PSII-, and HPPD-inhibiting herbicides and 2,4-D. Herbicide use history for the field in which CHR was discovered indicates no previous use of 2,4-D.
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Dayan, Franck E., Maria L. B. Trindade y Edivaldo D. Velini. "Amicarbazone, a New Photosystem II Inhibitor". Weed Science 57, n.º 6 (diciembre de 2009): 579–83. http://dx.doi.org/10.1614/ws-09-099.1.
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Amicarbazone is a new triazolinone herbicide with a broad spectrum of weed control. The phenotypic responses of sensitive plants exposed to amicarbazone include chlorosis, stunted growth, tissue necrosis, and death. Its efficacy as both a foliar- and root-applied herbicide suggests that absorption and translocation of this compound is very rapid. This new herbicide is a potent inhibitor of photosynthetic electron transport, inducing chlorophyll fluorescence and interrupting oxygen evolution ostensibly via binding to the QB domain of photosystem II (PSII) in a manner similar to the triazines and the triazinones classes of herbicides. As a result, its efficacy is susceptible to the most common form of resistance to PSII inhibitors. Nonetheless, amicarbazone has a good selectivity profile and is a more potent herbicide than atrazine, which enables its use at lower rates than those of traditional photosynthetic inhibitors.
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Takano, Hudson Kagueyama, Rubem Silvério de Oliveira Junior, Jamil Constantin, Guilherme Braga Pereira Braz, Luiz Henrique Morais Franchini y Nilda Roma Burgos. "Multiple resistance to atrazine and imazethapyr in hairy beggarticks (Bidens pilosa )". Ciência e Agrotecnologia 40, n.º 5 (octubre de 2016): 547–54. http://dx.doi.org/10.1590/1413-70542016405022316.
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ABSTRACT Resistance to herbicides is a serious threat to crop production worldwide, especially in agronomic crops and cereals. This research evaluated the possible occurrence of Bidens pilosa resistant to imazethapyr and atrazine in Brazil. The resistant biotype was collected from an area with a history of repeated application of photosystem II (PSII) and ALS inhibitor herbicides. The susceptible biotype was collected from an area with no history of herbicide application. Resistance verification experiments were carried out in the greenhouse. The treatments were arranged in a 3 x 8 factorial scheme, where the first factor was populations [susceptible (S), parent resistant (PR), and resistant F1 (RF1)]; and the second factor was herbicide dose (0, 375, 750, 1500, 3000, 6000, 12000 and 24000 g ha-1 for atrazine; or 0, 12.5, 25, 50, 100, 200, 400 and 800 g ha-1 for imazethapyr). The resistance factor to atrazine was 2.83 for PR and 5.55 for RF1. This population was more resistant to imazethapyr (>21-fold) than it was to atrazine. The recommended maximum dose of the herbicides did not control this B. pilosa population adequately. The data support the claim that B. pilosa population from this field in Quarto Centenário, Parana is resistant to two herbicide modes of action - PSII inhibitor (i.e. atrazine) and ALS inhibitor (i.e. imazethapyr). This is the first report of such case for this species, globally. Cross-resistance to other ALS inhibitors and other PS II inhibitors as well as the respective mechanisms of resistance to each herbicide are being investigated.
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Sarangi, Debalin, Trey Stephens, Abigail L. Barker, Eric L. Patterson, Todd A. Gaines y Amit J. Jhala. "Protoporphyrinogen oxidase (PPO) inhibitor–resistant waterhemp (Amaranthus tuberculatus) from Nebraska is multiple herbicide resistant: confirmation, mechanism of resistance, and management". Weed Science 67, n.º 05 (12 de julio de 2019): 510–20. http://dx.doi.org/10.1017/wsc.2019.29.
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AbstractA waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] biotype (designated as “NER”) collected from a soybean [Glycine max (L.) Merr.] production field in eastern Nebraska survived the POST application of fomesafen at the labeled rate. The objectives of this study were to (1) quantify the level of resistance to protoporphyrinogen oxidase (PPO) inhibitors (acifluorfen, fomesafen, and lactofen) applied POST, (2) determine the mechanism of PPO-inhibitor resistance in the NER biotype, (3) determine whether NER possessed multiple resistance to acetolactate synthase (ALS)-, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS)-, and photosystem II (PSII)-inhibiting herbicides, and (4) control NER with POST soybean herbicides. A whole-plant dose–response bioassay revealed that the NER biotype was 4- to 6-fold resistant to PPO-inhibiting herbicides depending on the known susceptible biotype (S1 or S2) used for comparison. A Kompetitive Allele Specific PCR (KASP™) assay was developed and performed for rapid and robust detection of the ΔG210 mutation (deletion of a codon) in the PPX2L gene. All samples of the NER biotype tested positive for the ΔG210 mutation. Dose–response bioassays confirmed that the NER biotype was resistant to three additional herbicide sites of action. Chlorimuron and imazethapyr, both ALS inhibitors, applied at 32X the labeled rate resulted in <80% reduction in the aboveground biomass of the NER biotype. The same biotype was 3- and 7-fold resistant to glyphosate (EPSPS inhibitor) and atrazine (PSII inhibitor), respectively. Glufosinate, 2,4-D choline plus glyphosate, and dicamba were the only soybean POST herbicides that controlled NER effectively (≥92% aboveground biomass reduction). Amaranthus tuberculatus is the first confirmed weed species in Nebraska to evolve resistance to four distinct herbicide sites of action, leaving no POST herbicide choice for effective control in glyphosate-resistant and conventional (non-transgenic) soybean.
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Schultz, John L., Laura A. Chatham, Chance W. Riggins, Patrick J. Tranel y Kevin W. Bradley. "Distribution of Herbicide Resistances and Molecular Mechanisms Conferring Resistance in Missouri Waterhemp (Amaranthus rudisSauer) Populations". Weed Science 63, n.º 1 (marzo de 2015): 336–45. http://dx.doi.org/10.1614/ws-d-14-00102.1.
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A survey of soybean fields containing waterhemp was conducted just prior to harvest in 2012 to determine the scope and extent of herbicide resistance and multiple herbicide resistances among a sample of Missouri waterhemp populations. Resistance was confirmed to glyphosate and to acetolactate synthase (ALS), protoporphyrinogen oxidase (PPO), photosystem II (PSII), and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors, but not to 2,4-D. Of the 187 populations tested, 186 exhibited resistance to chlorimuron. The proportions of populations with atrazine or glyphosate resistance were similar, with 30 and 29% of the populations surviving the 3× rates. Lactofen resistance was observed in 5% of the populations, whereas mesotrione resistance was only found in 1.6% of the populations. All populations tested were susceptible to 2,4-D at the 3× rate. At least 52% of the waterhemp populations tested exhibited resistance to herbicides from two mechanism of action. Resistance to atrazine plus chlorimuron as well as glyphosate plus chlorimuron was present in 29% of the populations. Three-way resistance, primarily comprised of resistance to atrazine plus chlorimuron plus glyphosate, was present in 11% of the populations. Resistance to herbicides from four mechanisms of action was found in 2% of the populations, and one population exhibited resistance to herbicides from five mechanisms of action. DNA analysis of a subsample of plants revealed that previously documented mechanisms of resistance in waterhemp, including the ΔG210 deletion conferring PPO-inhibitor resistance, the Trp574Leu amino acid substitution conferring ALS-inhibitor resistance, and elevated 5-enolypyruvyl-shikimate-3-phosphate synthase copy number and the Pro106Ser amino acid substitution resulting in glyphosate resistance, explained survival in many, but not all, instances. Atrazine resistance was not explained by the Ser264Gly D1 protein substitution. Overall, results from these experiments indicate that Missouri soybean fields contain waterhemp populations with resistance to glyphosate, ALS-, PPO-, PSII-, and HPPD-inhibiting herbicides, which are some of the most common mechanisms of action currently utilized for the control of this species in corn and soybean production systems. Additionally, these results indicate that slightly more than half of the populations tested exhibit resistance to more than one herbicide mechanisms of action. Managing the current resistance levels in existing populations is of utmost importance. The use of multiple, effective herbicide modes of action, both preemergence and postemergence, and the integration of optimum cultural and mechanical control practices will be vital in the management of Missouri waterhemp populations in the future.
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McMurray, Larn S., Christopher Preston, Albert Vandenberg, Dili Mao, Kirstin E. Bett y Jeffrey G. Paull. "Induced novelpsbAmutation (Ala251to Thr) in higher plants confers resistance to PSII inhibitor metribuzin inLens culinaris". Pest Management Science 75, n.º 6 (20 de febrero de 2019): 1564–70. http://dx.doi.org/10.1002/ps.5328.
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McKenzie-Gopsill, Andrew, Gavin Graham, Martin Laforest, Sebastian Ibarra, Sheldon Hann y Cameron Wagg. "Occurrence and Management of PSII-Inhibitor-Resistant Chenopodium album L. in Atlantic Canadian Potato Production". Agronomy 10, n.º 9 (11 de septiembre de 2020): 1369. http://dx.doi.org/10.3390/agronomy10091369.
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Potato producers in the Atlantic Canadian provinces of New Brunswick (NB) and Prince Edward Island (PE) rely on the photosystem II-inhibiting herbicide metribuzin for weed management. Recently, potato producers in the region have reported unacceptable common lambsquarters control following an application of metribuzin. Tissue and seed samples were collected from escaped common lambsquarters populations from across the potato producing regions of NB and PE and screened for the Ser264Gly mutation in psbA. Overall, 46% of sampled populations possessed the Ser264Gly mutation across the region. Cross-resistance testing to atrazine, metribuzin and linuron confirmed populations with the Ser264Gly were resistant to triazines and triazinones but remained susceptible to linuron. Dose response analysis determined a moderate level of resistance to metribuzin in common lambsquarters which would not be controlled in producers fields. A field experiment was conducted in Fredericton, NB and Harrington, PE, to determine if currently registered and unregistered products and tank-mixes would control PSII-inhibitor-resistant common lambsquarters in potato. All evaluated products, with the exception of S-metolachlor, provided control equivalent to the weed-free check without compromising potato yield or quality. This study demonstrates that PSII-inhibitor-resistant common lambsquarters are found in Atlantic Canadian potato production systems, but can be controlled with currently registered herbicides and rates with alternative modes of action.
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Brosnan, James T., Gregory K. Breeden, Jose J. Vargas y Logan Grier. "A Biotype of Annual Bluegrass (Poa annua) in Tennessee Is Resistant to Inhibitors of ALS and Photosystem II". Weed Science 63, n.º 1 (marzo de 2015): 321–28. http://dx.doi.org/10.1614/ws-d-14-00080.1.
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Annual bluegrass resistance to inhibitors of acetolactate synthase (ALS) and photosystem II (PSII) in managed turf has been confirmed in the southeastern United States. A biotype of annual bluegrass that had developed resistance (R) to the PSII inhibitor simazine was not controlled by POST applications of foramsulfuron or trifloxysulfuron in 2011 or 2012. In whole plant dose-response experiments, trifloxysulfuron, simazine, and indaziflam controlled a susceptible (S) population of annual bluegrass > 91% when applied POST to nontillering plants. However, trifloxysulfuron applications at 3.5 to 223 g ai ha−1only controlled R annual bluegrass ≤ 40%. Similarly, simazine at 140 to 9,000 g ai ha−1only controlled R annual bluegrass ≤ 20%. R annual bluegrass plants were more tolerant to indaziflam applied POST to leaf stage plants prior to tillering, as rates > 100 g ai ha−1were needed to control R annual bluegrass ≥ 96%. No differences in the activity of ALS in R and S plants exposed to increasing foramsulfuron concentrations from 0 to 100 µM were detected suggesting that nontarget mechanisms could explain reduced efficacy of POST herbicide applications in whole plant dose-response experiments. Applications of indaziflam (35 to 70 g ha−1) and oxadiazon (2,240 to 4,500 g ai ha−1) effectively controlled R annual bluegrass when applied PRE. This biotype of R annual bluegrass is the first reported instance of a weed developing resistance to multiple modes of action in managed turf. Education is needed among turf managers regarding the consequences of exclusive use of the same herbicides for annual bluegrass control leading to the onset of herbicide resistance.
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Vennapusa, Amaranatha Reddy, Felipe Faleco, Bruno Vieira, Spencer Samuelson, Greg R. Kruger, Rodrigo Werle y Mithila Jugulam. "Prevalence and Mechanism of Atrazine Resistance in Waterhemp (Amaranthus tuberculatus) from Nebraska". Weed Science 66, n.º 5 (septiembre de 2018): 595–602. http://dx.doi.org/10.1017/wsc.2018.38.
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AbstractResistance to atrazine (a photosystem II [PSII] inhibitor) is prevalent in waterhemp [Amaranthus tuberculatus(Moq.) J. D. Sauer] across the U.S. Midwest. Previous research suggests that target-site mutation or rapid metabolism of atrazine mediated by glutathioneS-transferase (GST) conjugation confers resistance inA. tuberculatusfrom Illinois. The distribution and mechanism of resistance to atrazine inA. tuberculatuspopulations from Nebraska (NE) are unknown. In this research we (1) evaluated the response and frequency of resistance in NEA. tuberculatusto soil-applied PSII (metribuzin and atrazine) and protoporphyrinogen oxidase (sulfentrazone) inhibitors, as well as POST-applied atrazine; and (2) determined the mechanism of atrazine resistance in NEA. tuberculatus. The chloroplasticpsbAgene, coding for a D1 protein (the target site of atrazine) was sequenced in 85 plants representing 27 populations ofA. tuberculatus. Furthermore, 24 plants selected randomly from four atrazine-resistant (AR) populations were used to determine the metabolism of atrazine via GST conjugation. Results from the soil-applied herbicide evaluation suggest that metribuzin (0.56 kg ai ha−1) and sulfentrazone (0.28 kg ai ha−1) were effective onA. tuberculatusmanagement. PRE and POST screenings against atrazine in the greenhouse indicate that atrazine (1.345 kg ai ha−1) was not effective on 39% and 73% of theA. tuberculatuspopulations evaluated (total of 109 and 85 populations, respectively), suggesting the prevalence of atrazine resistance inA. tuberculatusin NE. Sequence analysis of thepsbAgene found no known point mutations conferring atrazine resistance. However, the AR plants conjugated atrazine via GST activity faster than the known atrazine-susceptibleA. tuberculatus. Overall, the outcome of this study demonstrates the predominance of metabolism-based resistance to atrazine inA. tuberculatusfrom NE, which may predispose this species to evolve resistance to other herbicides. The use of integrated management strategies forA. tuberculatusis crucial for the control of this troublesome species.
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Singh, Vijay, Russ Garetson, Josh McGinty, Peter Dotray, Gaylon Morgan, Scott Nolte y Muthukumar Bagavathiannan. "Distribution of herbicide-resistant waterhemp (Amaranthus tuberculatus) across row crop production systems in Texas". Weed Technology 34, n.º 1 (26 de septiembre de 2019): 129–39. http://dx.doi.org/10.1017/wet.2019.78.
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AbstractWe conducted a survey in the major row-crop production regions of Texas to determine the response of waterhemp to glyphosate (5-enolpyruvylshikimate-3-phosphate synthase [EPSPS] inhibitor), atrazine (photosystem II [PSII] inhibitor), pyrithiobac (acetolactate synthase [ALS] inhibitor), tembotrione (hydroxyphenylpyruvate dioxygenase [HPPD] inhibitor), fomesafen (protoporphyrinogen oxidase [PPO] inhibitor), and dicamba (synthetic auxin). We evaluated 127 accessions for these herbicides. Resistance was confirmed on the basis of plant survival within an accession, and the injury ratings of surviving plants were used to categorize each accession as resistant (<50% injury) or less sensitive (50% to 89% injury). For glyphosate, approximately 27% of all tested accessions were resistant and 20% were less sensitive. The Gulf Coast region had the most glyphosate-resistant accessions (46% of the accessions from this region), followed by the Blacklands region (9%). A dose-response assay of the most resistant waterhemp accession (TX-25) exhibited 17-fold resistance to glyphosate when compared with a susceptible standard. Waterhemp resistance to atrazine also was common in the Gulf Coast region. The accession with the greatest atrazine resistance (TX-31) exhibited 47- and 68-fold resistance to this herbicide when applied POST and PRE, respectively. Widespread resistance to pyrithiobac was observed in waterhemp accessions throughout the Blacklands and Gulf Coast regions. The most resistant accession identified in this study was 61-fold resistant compared with a susceptible standard. No high-level resistance was detected for tembotrione, dicamba, or fomesafen, but high variability in sensitivity to tembotrione and dicamba was observed. One waterhemp accession exhibited reduced sensitivity to fomesafen; the rest were sensitive. Overall, at least two accessions exhibited resistance or reduced sensitivity to herbicides with five different sites of action. The study illustrates the prevalence of multiple herbicide resistance in waterhemp accessions in Texas and emphasizes the need to implement diversified management tactics.
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Svyantek, Andrej W., Phillipe Aldahir, Shu Chen, Michael L. Flessner, Patrick E. McCullough, Sudeep S. Sidhu y J. Scott McElroy. "Target and Nontarget Resistance Mechanisms Induce Annual Bluegrass (Poa annua) Resistance to Atrazine, Amicarbazone, and Diuron". Weed Technology 30, n.º 3 (septiembre de 2016): 773–82. http://dx.doi.org/10.1614/wt-d-15-00173.1.
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Annual bluegrass is a weed species in turfgrass environments known for exhibiting resistance to multiple herbicide modes of action, including photosystem II (PSII) inhibitors. To evaluate populations of annual bluegrass for susceptibility to PSII inhibitors of varied chemistries, populations were treated with herbicides from triazolinone, triazine, and substituted urea families: amicarbazone, atrazine, and diuron, respectively. Sequencing of thepsbAgene confirmed the presence of a Ser264to Gly amino acid substitution within populations that exhibited resistance to both atrazine and amicarbazone. A single biotype, DR3, which lacked any previously reportedpsbAgene point mutation, exhibited resistance to diuron, atrazine, and amicarbazone. DR3 had a significantly lower rate of absorption and translocation of atrazine and had enhanced atrazine metabolism when compared with both the Ser264to Gly resistant mutant and susceptible biotypes. We thus report possible nontarget mechanisms of resistance to PSII-inhibiting herbicides in annual bluegrass.
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Brosnan, James T., Jose J. Vargas, Gregory K. Breeden, Sarah L. Boggess, Margaret A. Staton, Phillip A. Wadl y Robert N. Trigiano. "Controlling Herbicide-Resistant Annual Bluegrass (Poa annua) Phenotypes with Methiozolin". Weed Technology 31, n.º 3 (22 de mayo de 2017): 470–76. http://dx.doi.org/10.1017/wet.2017.13.
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Methiozolin is an isoxazoline herbicide being investigated for selective POST annual bluegrass control in managed turfgrass. Research was conducted to evaluate methiozolin efficacy for controlling two annual bluegrass phenotypes with target-site resistance to photosystem II (PSII) or enolpyruvylshikimate-3-phosphate synthase (EPSPS)-inhibiting herbicides (i.e., glyphosate), as well as phenotypes with multiple resistance to microtubule and EPSPS or PSII and acetolactate synthase (ALS)-inhibiting herbicides. All resistant phenotypes were established in glasshouse culture along with a known herbicide-susceptible control and treated with methiozolin at 0, 125, 250, 500, 1000, 2000, 4000, or 8000 g ai ha−1. Methiozolin effectively controlled annual bluegrass with target-site resistance to inhibitors of EPSPS, PSII, as well as multiple resistance to EPSPS and microtubule inhibitors. Methiozolin rates required to reduce aboveground biomass of these resistant phenotypes 50% (GR50 values) were not significantly different from the susceptible control, ranging from 159 to 421 g ha−1. A phenotype with target-site resistance to PSII and ALS inhibitors was less sensitive to methiozolin (GR50=862 g ha−1) than a susceptible phenotype (GR50=423 g ha−1). Our findings indicate that methiozolin is an effective option for controlling select annual bluegrass phenotypes with target-site resistance to several herbicides.
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Perry, D. H., J. S. McElroy, F. Dane, E. van Santen y R. H. Walker. "Triazine-Resistant Annual Bluegrass (Poa annua) Populations with Ser264Mutation Are Resistant to Amicarbazone". Weed Science 60, n.º 3 (septiembre de 2012): 355–59. http://dx.doi.org/10.1614/ws-d-11-00200.1.
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Amicarbazone is a photosystem II (PSII)-inhibiting herbicide in the triazolinone family, which is similar in mode of action to the triazines. Annual bluegrass is a cool-season weed and has shown resistance to some PSII-inhibiting herbicides. The objective was to evaluate triazine-resistant and -susceptible annual bluegrass populations for potential cross-resistance to amicarbazone. Two triazine-resistant (MS-01, MS-02) and triazine-susceptible (AL-01, COM-01) annual bluegrass populations were treated with amicarbazone, atrazine, and simazine at 0.26, 1.7, and 1.7 kg ai ha−1, respectively. All herbicide treatments controlled the susceptible populations greater than 94% 2 wk after treatment (WAT). No visual injury of MS-01 and MS-02 was observed at any time following herbicide treatment. Quantum yield (ΦPSII) of annual bluegrass was measured 0 to 72 h after application (HAA) to determine the photochemical effects of amicarbazone compared to other PSII inhibitors. ΦPSIIof triazine-susceptible populations was reduced at all measurement times by all three herbicides. However, amicarbazone decreased ΦPSIIof susceptible populations faster and greater than atrazine and simazine at most measurement times. Amicarbazone did not reduce ΦPSIIof the MS-01 population. Amicarbazone significantly reduced ΦPSIIof the MS-02 population during several measurement timings; however, these reductions were short-lived compared to the susceptible populations and no trend in ΦPSIIreduction was observed. Sequencing of thepsbAgene revealed a Ser to Gly substitution at amino acid position 264 known to confer resistance to triazine herbicides. These data indicate amicarbazone efficiently inhibited PSII of susceptible annual bluegrass populations; however, triazine-resistant annual bluegrass populations with Ser264to Gly mutations are cross-resistant to amicarbazone.
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Davis, Gareth, Jocelyne Letarte, Christopher M. Grainger, Istvan Rajcan y François J. Tardif. "Widespread herbicide resistance in pigweed species in Ontario carrot production is due to multiple photosystem II mutations". Canadian Journal of Plant Science 100, n.º 1 (1 de febrero de 2020): 56–67. http://dx.doi.org/10.1139/cjps-2019-0114.
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The apparent efficacy of linuron to control pigweeds (Amaranthus spp.) has declined in Ontario, Canada, in past decades, possibly due to resistance. Samples were collected in multiple fields across Ontario with reported linuron failure. These were characterized at the whole-plant and molecular levels. Screening with linuron revealed resistance in six out of nine green pigweed (Amaranthus powellii Wats.) populations and 36 out of 38 populations of redroot pigweed (Amaranthus retroflexus L.). Sequencing of the psbA gene showed resistant plants had mutations conferring resistance to photosystem II (PSII) inhibitors. The most commonly seen mutation was coding for a Val219Ile substitution, while other populations had Ala251Val or Phe274Val. Two populations were documented with a double mutation at Val219Ile and Phe274Val. All substitutions endowed plants with low to moderate resistance to linuron, with various levels of cross resistance to other PSII inhibitors. The double mutants were characterized by higher levels of resistance to linuron and diuron compared with each single substitution. The widespread failure of linuron to control pigweed species in many carrot fields in Ontario is due to the selection of PSII mutants. This is the first report of double mutation in psbA in any weed species and the first report of Ala251Val and Phe273Val in pigweed species. The presence of a double mutation is probably the result of continuous selection of plants already resistant due to a single mutation. Our results illustrate the need for diversified weed management strategies in crops where herbicide options are limited.
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Pedroso, Rafael M., Kassim Al-Khatib, Ibrahim Abdallah, Rocio Alarcón-Reverte y Albert J. Fischer. "Resistance to Propanil in Ricefield Bulrush (Schoenoplectus mucronatus) Is Conferred by apsbAMutation, Val219to Ile". Weed Science 64, n.º 4 (diciembre de 2016): 562–69. http://dx.doi.org/10.1614/ws-d-16-00010.1.
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Determining the mechanisms of herbicide resistance in weeds allows for the development and implementation of applied management practices aimed to control and to prevent further spread of herbicide-resistant populations in crop fields. This research was conducted to determine propanil resistance and cross-resistance to other photosystem II (PSII) inhibitors in ricefield bulrush biotypes and to elucidate the mechanism of propanil resistance. To this end, propanil-resistant (R) and propanil-susceptible (S) biotypes were selected from field-collected populations after propanil spraying at the field rate, and whole-plant, dose–response experiments were conducted to evaluate cross-resistance to PSII inhibitors and interactions between propanil and the insecticides malathion and carbaryl. In addition, thepsbAgene from R and S biotypes was sequenced for amino acid alterations following polymerase chain reaction (PCR) amplification. Plant survival data indicated the R biotype displayed a 14-fold increase in propanil resistance relative to the susceptible (S) biotype. In addition, the propanil-R biotype also had increased resistance to the PSII-inhibitors bromoxynil, diuron, and metribuzin but was more susceptible to bentazon than were propanil-S plants. Synergism between propanil and the insecticides carbaryl and malathion was greater in the S biotype than it was in the R biotype, indicating that, unlike propanil resistance in weedy grasses, enhanced degradation of the herbicide molecule is not a mechanism of resistance for propanil in ricefield bulrush. A Val219to Ile substitution in the propanil-R chloroplast D1 protein was identified following sequencing of thepsbAgene. This research suggests a single-point mutation at the target site causes resistance to propanil, diuron, metribuzin, and bromoxynil but increasing susceptibility to bentazon in propanil-R ricefield bulrush, a novel Val219–Ile feature. To our knowledge, this is the first instance of propanil resistance in weeds because of a mechanism other than enhanced herbicide metabolism. Tank-mixing bentazon and propanil, where permitted, can control both propanil-R and propanil-S biotypes.
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Silva, Paulo, Young–Jun Choi, Hanadi A. G. Hassan y Peter J. Nixon. "Involvement of the HtrA family of proteases in the protection of the cyanobacterium Synechocystis PCC 6803 from light stress and in the repair of photosystem II". Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 357, n.º 1426 (29 de octubre de 2002): 1461–68. http://dx.doi.org/10.1098/rstb.2002.1146.
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Photosystem II (PSII) is prone to irreversible light–induced damage, with the D1 polypeptide a major target. Repair processes operate in the cell to replace a damaged D1 subunit within the complex with a newly synthesized copy. As yet, the molecular details of PSII repair are relatively obscure despite the critical importance of this process for maintaining PSII activity and cell viability. We are using the cyanobacterium Synechocystis sp. PCC 6803 to identify the various proteases and chaperones involved in D1 turnover in vivo . Two families of proteases are being studied: the FtsH family (four members) of Zn 2+ –activated nucleotide–dependent proteases; and the HtrA (or DegP) family (three members) of serine–type proteases. In this paper, we report the results of our studies on a triple mutant in which all three copies of the htrA gene family have been inactivated. Growth of the mutant on agar plates was inhibited at high light intensities, especially in the presence of glucose. Oxygen evolution measurements indicated that, under conditions of high light, the rate of synthesis of functional PSII was less in the mutant than in the wild–type. Immunoblotting experiments conducted on cells blocked in protein synthesis further indicated that degradation of D1 was slowed in the mutant. Overall, our observations indicate that the HtrA family of proteases are involved in the resistance of Synechocystis 6803 to light stress and play a part, either directly or indirectly, in the repair of PSII in vivo .
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Savitch, Leonid V., Tessa Pocock, Marianna Krol, Kenneth E. Wilson, Bruce M. Greenberg y Norman P. A. Huner. "Effects of growth under UVA radiation on CO2 assimilation, carbon partitioning, PSII photochemistry and resistance to UVB radiation in Brassica napus cv. Topas". Functional Plant Biology 28, n.º 3 (2001): 203. http://dx.doi.org/10.1071/pp00116.
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The effects of growth of Brassica napus L. cv. Topas under PAR or PAR+UVA radiation was assessed with respect to sensitivity to subsequent exposure to UVB radiation. Despite the fact that growth under PAR+UVA induced minimal effects in photosystem II (PSII) photochemistry, growth under PAR+UVA inhibited the accumulation of the photosynthetic end products, sucrose and starch. This was associated with a decreased capacity for ribulose 1,5-bisphosphate (RuBP) regeneration, a decreased capacity for light- and CO 2 -saturated rates of CO2 assimilation, a decrease in the apparent quantum yield for CO2 assimilation, an over-reduction of chloroplast stroma, an increased susceptibility to the feedback effects on photosynthesis and a stimulation of glycolysis compared to controls grown under PAR. Subsequent exposure to UVB decreased the maximum Rubisco activity in leaves of both PAR- and PAR+UVA-grown plants. However, the decrease in the capacity for CO2 assimilation in PAR-grown plants exposed to UVB did not appear to be associated with limitations at the level of PSII linear electron transport, but rather with a decreased capacity for sucrose biosynthesis, limited triose-P utilization and a decreased capacity for RuBP regeneration. In contrast, the decreased capacity for CO 2 assimilation in PAR+UVA-grown plants exposed to UVB was associated with an inhibition of PSII photochemistry and a decreased supply of ATP. Thus, growth under UVA radiation appears to induce feedback-limited photosynthesis and does not enhance resistance of Brassica napus to UVB radiation.
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Broster, J. C., J. E. Pratley, R. H. L. Ip, L. Ang y K. P. Seng. "A quarter of a century of monitoring herbicide resistance in Lolium rigidum in Australia". Crop and Pasture Science 70, n.º 3 (2019): 283. http://dx.doi.org/10.1071/cp18584.
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Charles Sturt University has operated a commercial herbicide resistance testing service since 1991, following a random survey of the South West Slopes region of New South Wales that identified significant incidence of herbicide resistance in annual ryegrass (Lolium rigidum Gaud.). Other surveys of cropping regions of southern Australia conducted at that time also found a significant incidence of resistance. In the subsequent 25-year period, the testing service has received samples from the majority of the southern Australian cropping belt. Overall, 80% of samples tested were resistant to acetyl-CoA carboxylase (ACCase) inhibiting aryloxyphenoxypropionate and phenylpyrazole herbicides, 56% to acetolactate synthase (ALS) inhibiting herbicides, and 24% to ACCase-inhibiting cyclohexanedione herbicides. The incidences of resistance to inhibitors of photosynthesis at PSII, tubulin-formation inhibitors, and 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase inhibiting herbicides have remained <10% of samples tested. The relationships between many herbicide groups and subgroups are discussed, as is the variability in resistance incidence and the forms of cross or multiple resistance for each state. This paper builds on an earlier publication of 14 years of testing history. At >5000 samples, the size and geographical spread of this dataset allows for valuable analyses of the relationships present in herbicide-resistant populations of annual ryegrass.
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O’Brien, Sarah R., Adam S. Davis y Dean E. Riechers. "Quantifying Resistance to Isoxaflutole and Mesotrione and Investigating Their Interactions with Metribuzin POST in Waterhemp (Amaranthus tuberculatus)". Weed Science 66, n.º 5 (septiembre de 2018): 586–94. http://dx.doi.org/10.1017/wsc.2018.36.
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AbstractGreenhouse experiments were conducted to quantify resistance levels to the 4-hydroxyphenyl-pyruvate dioxygenase (HPPD)-inhibiting herbicides mesotrione (MES) and isoxaflutole (IFT) in NEB (Nebraska HPPD- and atrazine-resistant) and SIR (Stanford, IL, HPPD- and atrazine-resistant) waterhemp [Amaranthus tuberculatus(Moq.) J. D. Sauer] populations. These populations differ in their field-use histories and resistance levels to MES. Foliar growth responses were compared with ACR (HPPD sensitive; metabolic atrazine-resistant) and SEN (sensitive to HPPD and photosystem II [PSII] inhibitors). A greenhouse dose–response study was conducted with each herbicide at two POST timings: early (EPOST) (5 cm; 4 to 5 true leaves) and POST (10 cm; 8 to 9 true leaves). At the EPOST timing, SIR was 10-fold resistant to IFT and 32-fold resistant to MES, while NEB was 4-fold resistant to IFT and 7-fold resistant to MES when compared with ACR. At the POST timing, SIR was 17-fold resistant to IFT and 21-fold resistant to MES, while NEB was 3-fold resistant to IFT and 7-fold resistant to MES when compared with ACR. Results overall indicated greater fold-resistance levels to MES relative to IFT at each timing. However, POST treatments to SIR showed contrasting effects on resistance levels relative to EPOST. To investigate potential management strategies for resistantA. tuberculatuspopulations, a POST interaction study was conducted using combinations of metribuzin and either IFT or MES. A metribuzin rate (191 g ai ha−1) causing an approximately 20% biomass reduction was chosen for interaction studies and combined with varying rates of either IFT or MES. Results indicated 52.5 g ai ha−1of MES combined with metribuzin displayed a synergistic effect on biomass reduction in SIR. However, other combinations of either MES or IFT and metribuzin resulted in additive effects on biomass reduction in both HPPD-resistant populations. These results provide insights into the joint activity between HPPD and PSII inhibitors for controlling metabolism-based, multiple herbicide–resistantA. tuberculatus.
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Xu, Chang-Cheng, Liangbi Li y Tingyun Kuang. "Photoprotection in chilling-sensitive and -resistant plants illuminated at a chilling temperature: role of the xanthophyll cycle in the protection against lumen acidification". Functional Plant Biology 27, n.º 7 (2000): 669. http://dx.doi.org/10.1071/pp00009.
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The role of the xanthophyll cycle in the protection against photoinhibition of photosystem II (PSII) induced by chilling in moderate light was investigated in leaves of eight species or varieties of higher plants differing widely in chilling sensitivity. The extent of photoinhibition measured as the increase in the slowly reversible fluorescence quenching (qI) was found not to correlate with the overall amount of zeaxanthin formed during photo-inhibitory treatment. On the other hand, a strong, positive correlation existed between qI and the rate difference between the development of the rapidly relaxing, DpH-dependent quenching component (qf) and the formation of zeaxanthin (DR) across all examined species or varieties. There was also found to be a weaker, negative correlation between qI and the rate of zeaxanthin formation. Ascorbate feeding markedly increased the resistance to chilling-induced photoinhibition mainly by increasing the rate of zeaxanthin formation and therefore by decreasing DR. The possible implications of the present findings in explaining the mechanistic basis for the reversible, sustained photo-inhibition are discussed. It is suggested that the xanthophyll cycle may play a critical role in the protection of the thylakoid lumen against over-acidification and the resulting photoinhibition of PSII reaction centers.
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Dumont, Mélanie, Jocelyne Letarte y François J. Tardif. "Identification of apsbAMutation (Valine219to Isoleucine) in Powell Amaranth (Amaranthus powellii) Conferring Resistance to Linuron". Weed Science 64, n.º 1 (marzo de 2016): 6–11. http://dx.doi.org/10.1614/ws-d-15-00087.1.
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A Powell amaranth population suspected to be resistant (R) to linuron was discovered in a carrot field in Keswick, Ontario, Canada, in 1999. Dose–response analysis with different herbicides and DNA sequencing of thepsbAgene encoding the D1 protein of photosystem II were done to confirm the resistance and identify its basis. A calculated resistance factor indicated a 12-fold increased resistance when linuron was applied to an R population compared with a susceptible (S) population. Moreover, the R population showed 6.4- and 3.1-fold greater resistance to two other phenylurea herbicides (diuron and monolinuron), 1.8- and 1.4-fold greater resistance to two triazine herbicides (metribuzin and prometryn), and 2.6-fold greater resistance to the triazinone metribuzin. R population was also cross-resistant to bentazon and bromoxynil when compared with S population, with a calculated resistance factor of 1.4 and 2.2, respectively. The partial nucleotide sequence of thepsbAgene of R populations differed at two locations when compared with S populations. The first mutation coded for a Val219Ile substitution in the deduced amino acid sequence of the D1 protein, and the second mutation was silent and encoded for a proline at position 279 in both R and S populations. The Val219Ile substitution in thepsbAgene is most likely the cause of this Powell amaranth population resistance to linuron and other PSII inhibitors. This is the first recorded instance of a Val219Ile substitution in anAmaranthusspecies.
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Bashir, Sadia, Misbah Amir, Faiza Bashir, Muhammad Javed, Adnan Hussain, Saba Fatima, Rabia Parveen et al. "Structural and functional stability of photosystem-II in Moringa oleifera under salt stress". MAY 2021, n.º 15(05):2021 (10 de mayo de 2021): 676–82. http://dx.doi.org/10.21475/ajcs.21.15.05.p2996.
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The photosynthetic efficiency in plants is affected by salinity. Focus of this study was to observe the consequences of salinity on the rate of photosynthesis in Moringa (Moringa oleifera L.) plants. Experiment was conducted under field conditions with 3 replicates and data of treated and non-treated plants was collected accordingly. Photosynthetic rate was affected by different levels of salt stress. The change in photosynthetic was attributes were determined by OJIP and light response curve calculations by using Fluor Pen [FP 100-PS (Photon system, Czech Republic)] and DUAL-PAM-100 (Walz, Germany). Salinity stress decreased chlorophyll a fluorescence characteristic. The significant quantity of electron transport (φEo), quantum yield of primary photochemistry (φPo), proficiency per trapped excitation (Ψo) and performance index of photosystem II (PSII). Performance index (PIABS) was also declined with salinity in M. oleifera. Our results showed that electron transport rate and photosynthetic rate were inhibited by salinity in M. oleifera. However, in M. oleifera electron transport pathway of PSII was repressed and found varied in plants which are salt resistant. It was concluded that Y(I), ETR(I), Y(II), ETR(II), and Y(NA) were decreased by increasing salinity while NPQ, Y(ND), Y(NO) and Y(NPQ) increased in plants having resistance to salt stress
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Sherff, Carolyn M. y Brian Mulloney. "Passive Properties of Swimmeret Motor Neurons". Journal of Neurophysiology 78, n.º 1 (1 de julio de 1997): 92–102. http://dx.doi.org/10.1152/jn.1997.78.1.92.
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Sherff, Carolyn M. and Brian Mulloney. Passive properties of swimmeret motor neurons. J. Neurophysiol. 78: 92–102, 1997. Four different functional types of motor neurons innervate each swimmeret: return-stroke excitors (RSEs), power-stroke excitors (PSEs), return-stroke inhibitors (RSIs), and power-stroke inhibitors (PSIs). We studied the structures and passive electrical properties of these neurons, and tested the hypothesis that different types of motor neurons would have different passive properties that influenced generation of the swimmeret motor pattern. Cell bodies of neurons innervating one swimmeret were clustered in two anatomic groups in the same ganglion. The shapes of motor neurons in both groups were similar, despite the differences in locations of their cell bodies and in their functions. Diameters of their axons in the swimmeret nerve ranged from <2 to ∼35 μm. Resting membrane potentials, input resistances, and membrane time constants were recorded with microelectrodes in the processes of swimmeret motor neurons in isolated abdominal nerve cord preparations. Membrane potentials had a median of −59 mV, with 25th and 75th percentiles of −66.0 and −53 mV. The median input resistance was 6.4 MΩ, with 25th and 75th percentiles of 3.4 and 13.7 MΩ. Membrane time constants had a median of 9.3 ms, with 25th and 75th percentiles of 5.7 and 15.0 ms. Excitatory and inhibitory motor neurons had similar passive properties. RSE motor neurons were typically more depolarized than the other types, but the passive properties of RSE, PSE, RSI, and PSI neurons were not significantly different. Membrane time constants measured from cell bodies were briefer than those measured from neuropil processes, but membrane potentials and input resistances were not significantly different. The relative sizes of different motor neurons were measured from the sizes of their impulses recorded extracellularly from the swimmeret nerve. Smaller motor neurons had lower membrane potentials and were more likely to be active in the motor pattern than were large motor neurons. Motor neurons of different sizes had similar input resistances and membrane time constants. Motor neurons that were either oscillating or oscillating and firing in phase with the swimmeret motor pattern had lower average membrane potentials and longer time constants than those that were not oscillating. When the state of the swimmeret system changed from quiescence to continuous production of the motor pattern, the resting potentials, input resistances, and membrane time constants of individual swimmeret motor neurons changed only slightly. On average, both input resistance and membrane time constant increased. These similarities are considered in light of the functional task each motor neuron performs, and a hypothesis is developed that links the brief time constants of these neurons and graded synaptic transmission by premotor interneurons to control of the swimmeret muscles and the performance of the swimmeret system.
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Núñez, Constanza, Annegrett Palavecino, Iván A. González, Paulina Dreyse y Christian Erick Palavecino. "Effective Photodynamic Therapy with Ir(III) for Virulent Clinical Isolates of Extended-Spectrum Beta-Lactamase Klebsiella pneumoniae". Pharmaceutics 13, n.º 5 (22 de abril de 2021): 603. http://dx.doi.org/10.3390/pharmaceutics13050603.
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Background: The extended-spectrum beta-lactamase (ESBL) Klebsiella pneumoniae is one of the leading causes of health-associated infections (HAIs), whose antibiotic treatments have been severely reduced. Moreover, HAI bacteria may harbor pathogenic factors such as siderophores, enzymes, or capsules, which increase the virulence of these strains. Thus, new therapies, such as antimicrobial photodynamic inactivation (aPDI), are needed. Method: A collection of 118 clinical isolates of K. pneumoniae was characterized by susceptibility and virulence through the determination of the minimum inhibitory concentration (MIC) of amikacin (Amk), cefotaxime (Cfx), ceftazidime (Cfz), imipenem (Imp), meropenem (Mer), and piperacillin–tazobactam (Pip–Taz); and, by PCR, the frequency of the virulence genes K2, magA, rmpA, entB, ybtS, and allS. Susceptibility to innate immunity, such as human serum, macrophages, and polymorphonuclear cells, was tested. All the strains were tested for sensitivity to the photosensitizer PSIR-3 (4 µg/mL) in a 17 µW/cm2 for 30 min aPDI. Results: A significantly higher frequency of virulence genes in ESBL than non-ESBL bacteria was observed. The isolates of the genotype K2+, ybtS+, and allS+ display enhanced virulence, since they showed higher resistance to human serum, as well as to phagocytosis. All strains are susceptible to the aPDI with PSIR-3 decreasing viability in 3log10. The combined treatment with Cfx improved the aPDI to 6log10 for the ESBL strains. The combined treatment is synergistic, as it showed a fractional inhibitory concentration (FIC) index value of 0.15. Conclusions: The aPDI effectively inhibits clinical isolates of K. pneumoniae, including the riskier strains of ESBL-producing bacteria and the K2+, ybtS+, and allS+ genotype. The aPDI with PSIR-3 is synergistic with Cfx.
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Kutasy, Barbara, Zoltán Farkas, Balázs Kolics, Kincső Decsi, Géza Hegedűs, Judit Kovács, János Taller et al. "Detection of Target-Site Herbicide Resistance in the Common Ragweed: Nucleotide Polymorphism Genotyping by Targeted Amplicon Sequencing". Diversity 13, n.º 3 (10 de marzo de 2021): 118. http://dx.doi.org/10.3390/d13030118.
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Background: The spread of herbicide-resistance Ambrosia artemisiifolia threatens not only the production of agricultural crops, but also the composition of weed communities. The reduction of their spread would positively affect the biodiversity and beneficial weed communities in the arable habitats. Detection of resistant populations would help to reduce herbicide exposure which may contribute to the development of sustainable agroecosystems. Methods: This study focuses on the application of target-site resistance (TSR) diagnostic of A. artemisiifolia caused by different herbicides. We used targeted amplicon sequencing (TAS) on Illumina Miseq platform to detect amino acid changes in herbicide target enzymes of resistant and wild-type plants. Results: 16 mutation points of four enzymes targeted by four herbicide groups, such as Photosystem II (PSII), Acetohydroxyacid synthase (AHAS), 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) and protoporphyrinogen IX oxidase (PPO) inhibitors have been identified in common ragweed populations, so far. All the 16 mutation points were analyzed and identified. Out of these, two mutations were detected in resistant biotypes. Conclusions: The applied next-generation sequencing-targeted amplicon sequencing (NGS-TAS) method on A. artemisiifolia resistant and wild-type populations enable TSR detection of large sample numbers in a single reaction. The NGS-TAS provides information about the evolved herbicide resistance that supports the integrated weed control through the reduction of herbicide exposure which may preserve ecological properties in agroecosystems.
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Chaudhari, Sushila, Vijay K. Varanasi, Sridevi Nakka, Prasanta C. Bhowmik, Curtis R. Thompson, Dallas E. Peterson, Randall S. Currie y Mithila Jugulam. "Evolution of target and non-target based multiple herbicide resistance in a single Palmer amaranth (Amaranthus palmeri) population from Kansas". Weed Technology 34, n.º 3 (junio de 2020): 447–53. http://dx.doi.org/10.1017/wet.2020.32.
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AbstractThe evolution of resistance to multiple herbicides in Palmer amaranth is a major challenge for its management. In this study, a Palmer amaranth population from Hutchinson, Kansas (HMR), was characterized for resistance to inhibitors of photosystem II (PSII) (e.g., atrazine), acetolactate synthase (ALS) (e.g., chlorsulfuron), and EPSP synthase (EPSPS) (e.g., glyphosate), and this resistance was investigated. About 100 HMR plants were treated with field-recommended doses (1×) of atrazine, chlorsulfuron, and glyphosate, separately along with Hutchinson multiple-herbicide (atrazine, chlorsulfuron, and glyphosate)–susceptible (HMS) Palmer amaranth as control. The mechanism of resistance to these herbicides was investigated by sequencing or amplifying the psbA, ALS, and EPSPS genes, the molecular targets of atrazine, chlorsulfuron, and glyphosate, respectively. Fifty-two percent of plants survived a 1× (2,240 g ai ha−1) atrazine application with no known psbA gene mutation, indicating the predominance of a non–target site resistance mechanism to this herbicide. Forty-two percent of plants survived a 1× (18 g ai ha−1) dose of chlorsulfuron with proline197serine, proline197threonine, proline197alanine, and proline197asparagine, or tryptophan574leucine mutations in the ALS gene. About 40% of the plants survived a 1× (840 g ae ha−1) dose of glyphosate with no known mutations in the EPSPS gene. Quantitative PCR results revealed increased EPSPS copy number (50 to 140) as the mechanism of glyphosate resistance in the survivors. The most important finding of this study was the evolution of resistance to at least two sites of action (SOAs) (~50% of plants) and to all three herbicides due to target site as well as non–target site mechanisms. The high incidence of individual plants with resistance to multiple SOAs poses a challenge for effective management of this weed.
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Velikova, Violeta, Francesco Loreto, Tsonko Tsonev, Federico Brilli y Aglika Edreva. "Isoprene prevents the negative consequences of high temperature stress in Platanus orientalis leaves". Functional Plant Biology 33, n.º 10 (2006): 931. http://dx.doi.org/10.1071/fp06058.
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The phenomenon of enhanced plant thermotolerance by isoprene was studied in leaves of the same age of 1- or 2-year-old Platanus orientalis plants. Our goals were to determine whether the isoprene emission depends on the age of the plant, and whether different emission rates can influence heat resistance in plants of different age. Two-year-old plants emit greater amounts of isoprene and possess better capacity to cope with heat stress than 1-year-old plants. After a high temperature treatment (38°C for 4 h), photosynthetic activity, hydrogen peroxide content, lipid peroxidation and antiradical activity were preserved in isoprene emitting leaves of 1- and 2-year-old plants. However, heat inhibited photosynthesis and PSII efficiency, caused accumulation of H2O2, and increased all indices of membrane damage and antioxidant capacity in leaves of plants of both ages in which isoprene was inhibited by fosmidomycin. In isoprene-inhibited leaves fumigated with exogenous isoprene during the heat treatment, the negative effects on photosynthetic capacity were reduced. These results further support the notion that isoprene plays an important role in protecting photosynthesis against damage at high temperature. It is suggested that isoprene is an important compound of the non-enzymatic defence of plants against thermal stress, possibly contributing to scavenging of reactive oxygen species (ROS) and membrane stabilising capacity, especially in developed plants.
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Rojas-Lillo, Yesenia, Miren Alberdi, Patricio Acevedo, Claudio Inostroza-Blancheteau, Zed Rengel, Maria de la Luz Mora y Marjorie Reyes-Díaz. "Manganese toxicity and UV-B radiation differentially influence the physiology and biochemistry of highbush blueberry (Vaccinium corymbosum) cultivars". Functional Plant Biology 41, n.º 2 (2014): 156. http://dx.doi.org/10.1071/fp12393.
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Manganese (Mn2+) toxicity or UV-B radiation and their individual effects on plants have been documented previously. However, no study about the combined effect of these stresses is available. We evaluated the individual and combined effects of excess Mn2+ and UV-B radiation on physiological and biochemical parameters in two highbush blueberry (Vaccinium corymbosum L.) cultivars differing in resistance to Mn toxicity (Brigitta (resistant) and Bluegold (sensitive)). Plants grown in Hoagland nutrient solution were subjected to the following treatments: 2 µM MnCl2 (control), 500 µM MnCl2 (toxic Mn2+), UV-B radiation (a daily dose of 94.4 kJ m–2), and the combined treatment (toxic Mn2+ + UV-B) for 30 days. In both cultivars, the Mn2+ + UV-B treatment caused a more negative effect on net photosynthesis (Pn), stomatal conductance (gs), the photochemical parameters of PSII and the chl a/b ratio than the treatments with toxic Mn2+ or UV-B alone. However, Brigitta showed also a better acclimation response in Pn and gs than Bluegold at the end of the experiment. The Mn2+ + UV-B treatment inhibited growth, enhanced radical scavenging activity and superoxide dismutase activity, and increased the concentration of total UV-absorbing compounds, phenols and anthocyanins, mainly in Bluegold. In conclusion, Mn-resistant Brigitta showed a better acclimation response and greater resistance to the combined stress of Mn2+ toxicity and UV-B exposure than the Mn-sensitive Bluegold. An increased concentration of photoprotective compounds and enhanced resistance to oxidative stress in Brigitta could underpin increased resistance to the combined stress.
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Sheffer, Michal, Yiguo Hu, Ophir Shalem, Neville Sanjana, Eugen Dhimolea, Subhashis Sarkar, Megan A. Bariteau et al. "Genome-Scale Crispr-Cas9 Knockout Studies Reveal Mutifactorial and Functionally Overlapping Mechanisms of Myeloma Cell Resistance to Proteasome Inhibition". Blood 124, n.º 21 (6 de diciembre de 2014): 273. http://dx.doi.org/10.1182/blood.v124.21.273.273.
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Abstract Acquired or de novo resistance to established and investigational therapies represents a major clinical challenge for multiple myeloma (MM) and other neoplasias. Despite extensive efforts, clinically-validated molecular markers that predict for proteasome inhibitor (PSI) resistance in most MM patients remain elusive. This challenge is partly due to limited availability so far of molecular data on MM patients before the start of PSI treatment vs. immediately after resistance to it develops; this challenge may also reflect the heterogeneity of the complex molecular mechanisms regulating MM cell response to PSIs. We hypothesized that resistance to PSIs can be mediated by disruption of several functionally overlapping genes, and that the prevalence of any of these lesions may be too low to detect in datasets available thus far. To examine this latter hypothesis, we performed a genome-wide screen for genes whose loss confers to MM cells resistance against bortezomib, through the use of the CRISPR (clustered regularly interspaced short palindromic repeats)–associated nuclease Cas9 system. Specifically RPMI-8226 MM cells were transduced with lentiviral construct for Cas9 nuclease, followed by lentiviral delivery of a genome-scale pooled library of 123,411 single-guide RNAs (sgRNAs), which selectively align to target sequences at the 5′ constitutive exons of 18,080 genes and direct the Cas9 nuclease to cause double-stranded cleavage and loss of function of the respective gene. From the pool of MM cells transduced with the sgRNA library and treated with bortezomib, treatment-resistant cells were processed for deep sequencing, to identify enriched sgRNAs and their corresponding genes. We identified that loss-of-function of 33 candidate genes is associated with bortezomib resistance. We observed a high level of consistency between independent sgRNAs targeting the same gene, as well as a high rate of hit confirmation across different biological replicates. Notably, this set of candidate bortezomib-resistance genes was distinct from the "hits" we identified through a parallel CRISPR screen on the same cell line for resistance to a different targeted therapy (namely the bromodomain inhibitor JQ1), supporting the ability of this approach to identify treatment-specific resistance genes. These candidate bortezomib-resistance genes have documented or presumed roles in the regulation of extrinsic and intrinsic apoptotic cascades, autophagy, Toll-like receptor and NF-kappaB signaling, aggresome function, heat shock protein expression, chromatin remodeling, nutrient sensing, and tumor suppressor gene networks. Importantly, information from several publically available molecular profiling datasets converge to support the putative clinical relevance of these genes. For instance, gene expression data from tumor cells of bortezomib-naive patients with advanced MM revealed several transcriptional signatures of these candidate genes (defined by low transcript levels for any of the genes in the signature) which correlated with shorter time to disease progression after treatment with bortezomib (p<0.01, log-rank test), but not dexamethasone (p>0.426). Congruent with these findings, the highly bortezomib-responsive clinical setting of newly-diagnosed MM is associated with low cumulative frequency of mutations of these bortezomib-resistance genes (e.g. cumulative mutation rate of 3.9%, 95% confidence interval [CI] 1.25-6.55%). Notably, in other malignancies that are typically PSI-resistant, a higher cumulative frequency of such lesions is observed (average of ~28%, range 0-76%, 95% CI 22.46-32.70%; 57 datasets from 20+ neoplasias examined). In summary, this first application of the CRISPR/Cas9-based technology in MM illustrates its power to interrogate gene function on a genome-wide scale. This approach identifies bortezomib-resistance genes that are associated with pathways linked with the regulation of proteasome inhibitor response. Results from molecularly-annotated clinical samples converge to support a possible role for these genes in bortezomib resistance. This experience supports the value of CRISPR/Cas9-based studies to dissect the molecular mechanisms of treatment resistance in MM and other hematologic neoplasias (* equal contribution of M.S. and Y.H.). Disclosures Shalem: Broad Institute: Patent application for CRISPR technology Patents & Royalties. Sanjana:Broad Institute: Patent application for CRISPR technology Patents & Royalties. Zhang:Broad Institute: Patent application for CRISPR technology Patents & Royalties. Mitsiades:Johnson & Johnson: Research Funding; Amgen: Research Funding; Celgene: Consultancy, Honoraria; Millennium Pharmaceuticals: Consultancy, Honoraria.
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Fuks, Bruno, Fabrice Homble, Francoise Van Eycken, Hubert Figeys y Robert L. Lannoye. "Photoacoustic Spectroscopy as a Tool for Monitoring Herbicide Effects on Triazine-Resistant and -Susceptible Biotypes of Black Nightshade (Solanum nigrum)". Weed Science 40, n.º 3 (septiembre de 1992): 371–77. http://dx.doi.org/10.1017/s0043174500051766.
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Photoacoustic spectroscopy was used to study effects of atrazine and diuron on excised leaves of triazine-susceptible (S) and -resistant (R) biotypes of black nightshade. Changes of oxygen and photothermal components were compared to photochemical fluorescence quenching obtained by fluorimetry. After 1 h incubation in an aqueous solution of atrazine (0 to 200 μM), oxygen component of the photoacoustic signal was strongly decreased in the S biotype while the R biotype was not affected. Also, reoxidation of the primary quinone acceptor (QA−) of photosystem (PS) II of the S biotype was lower than that of the R biotype. With diuron treatments, changes in the characteristics of these biophysical signals were the same in both R and S biotypes. Both oxygen component and photochemical fluorescence quenching were decreased in treated leaves of the R and S biotypes. By using modulated oxygen and heat emissions, and the ratio of the initial inflection point (I) to the fluorescence maximum (P) as herbicide bioassay indicators, we showed that the photoacoustic spectroscopy was also a reliable technique for whole plant studies. Inhibition of photosynthesis was maximal 2 d after onset of treatment with atrazine (200 μM). Inhibitors of PSII did not induce a significant increase of heat emission in leaves which otherwise showed phytotoxic symptoms after treatment By using the photoacoustic technique, it was possible to obtain useful information on photosynthetic activity under herbicide stress, suggesting that pulsed oxygen emitted by leaves could be used to quantify susceptibility or to detect resistance to many types of photosynthetic inhibitors in weeds and crop plants.
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Pham, Lan V., Alex Rollo, Archito T. Tamayo, John Lee, Zhuang Zuo, Luhong Sun, Liang Zhang et al. "Biological Significance of the Immumoproteasome Subunits Mecl-1 and LMP-2 in Diffuse Large B-Cell Lymphoma." Blood 120, n.º 21 (16 de noviembre de 2012): 2717. http://dx.doi.org/10.1182/blood.v120.21.2717.2717.
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Abstract Abstract 2717 The biological significance of the ubiquitin-proteasome system in the control of cellular processes has been well-recognized; however, the pathophysiological importance of the immunoproteasome, the inducible form of the proteasome, has not been well-appreciated in cancer cells, particularly in this common diffuse large B-cell lymphoma (DLBCL), a clinically challenging, aggressive B-cell non-Hodgkin's lymphoma (NHL-B). The primary function of the immunoproteasome was originally believed to be only in immune cells to improve MHC-I antigen presentation efficiency in adaptive immune responses. It has now becomes evident that the immunoproteasome possesses broader biological functions, and is associated with various types of cancer. Using the Oncomine database to analyze the mRNA expression levels of immunoproteasome subunits in DLBCL, we found that the subunits MECL-1 and LMP-2 are highly expressed in comparison to normal B lymphocytes. We then examined the clinical significance of MECL-1 and LMP-2 mRNA expression in primary DLBCL, and found that increased MECL-1 mRNA expression is significantly associated with decreased cumulative overall survival rate (P=0.019). We then analyzed the protein expressions of MECL-1 and LMP-2 in various (20) DLBCL cell lines, and discovered that most of the DLBCL cell lines highly expressed both MECL-1 and LMP-2 but there is a subset of cell lines that did not express MECL-1 and LMP-2. Further analysis indicated that MECL-1 and LMP-2 subunits of the immunoproteasome are not associated with constitutive NF-kB activation in DLBCL since MECL-1 and LMP-2-negative DLBCL cell lines also express constitutive NF-kB activation. RNA interference-mediated knock-down of MECL-1 or LMP-2 leads to cell growth inhibition in DLBCL cell lines in vitro. These results strongly suggest that the immunoproteasome has important biological function in controlling growth and survival mechanisms in DLBCL and thus selective targeting of the immunoproteasome may offer therapeutic opportunity for this deadly disease. Bortezomib (BZ) is the first in the class of proteasome inhibitor (PSI) and represents a major advance in NHL, particularly mantle cell lymphoma. However, with the emergence of a new class of PSIs, such as Carfilzomib (CFZ), we are presented with opportunities to improve patient care in relapsed/refractory NHL-B. To elucidate the role of proteasome inhibitors in DLBCL, we analyzed the effect of BZ and CFZ in our representative DLBCL cell lines. BZ and CFZ treatments in DLBCL cell lines (20) have shown strong responses, with IC50s in the low nM ranges (2–50 nM). We have shown that DLBCL cell lines lacking both MECL-1 and LMP-2 are more resistant to CFZ than DLBCL cell lines that have both MECL-1 and LMP-2. To investigate a potential CFZ resistance mechanism(s) in these cell lines, we measured the 20S proteasome activity and compared this activity to the CFZ sensitive DLBCL cell lines. The results indicated that DLBCL cells that are more sensitive to CFZ show higher immunoproteasomal activity. The immunoproteasome activity in the resistant DLBCL cell lines is comparable to the proteasome activity found in normal B cells. These results suggest that the immunoproteasome is deregulated in DLBCL and represents a potential target for therapy in personalized medicine. Our studies emphasize understanding the mechanisms responsible for abnormal proteasomal function in DLBCL, that are critical for establishing an etiologic link to chemo-resistance and the development of new specific therapies for DLBCL targeting defective proteolysis through the immunoproteasome. Disclosures: No relevant conflicts of interest to declare.
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FRANCISCHINI, A., J. CONSTANTIN, R. S. OLIVEIRA JR, H. K. TAKANO y R. R. MENDES. "Multiple-and Cross-Resistance of Amaranthus retroflexus to Acetolactate Synthase (ALS) and Photosystem II (PSII) Inhibiting Herbicides in Preemergence". Planta Daninha 37 (2019). http://dx.doi.org/10.1590/s0100-83582019370100026.
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ABSTRACT: Herbicide resistance in Amaranthus genus occurs frequently around the word and has become a big problem in cotton producing areas. The objective of this work was to evaluate cross-and multiple-resistance of redroot pigweed (A. retroflexus) to herbicides used in preemergence in cotton fields in Brazil. Seven dose-response experiments were conducted with herbicides atrazine, prometryn, diuron, S-metolachlor, trifluralin, trifloxysulfuron-sodium and pyrithiobac-sodium, and the treatments consisted of application rates of 0, ¼, ½, 1, 2 and 4 times the recommended label rate. Eight A. retroflexus byotipes with suspect of resistance were sampled for experiments in three brazilian states of cotton producing. Resistance to prometryn was confirmed for one biotype in Goiás (GO), and one biotype from Mato Grosso (MT) showed cross-resistance to atrazine and prometryn. One byotipe from GO was identified with cross-resistance to trifloxysulfuron-sodium and pyrithiobac-sodium. One of the GO samples was identified with multiple resistance to prometryn and ALS inhibitors, another one to atrazine and ALS inhibitors, while MT byotipe was confirmed with multiple resistance to triazines and pyrithiobac. The herbicides S-metolachlor, diuron, and trifluralin were efficient for control of this species, therefore, they can be used as managment alternative in those regions.