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Stephen S Tobe - One of the best experts on this subject based on the ideXlab platform.
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Insect Juvenile Hormones in Plants
Studies in natural products chemistry, 2020Co-Authors: Jacqueline C Bede, Stephen S TobeAbstract:Abstract In the defence against insect herbivory, plants may produce compounds which interfere with the insect endocrine system [ 2, 3, 4 ]. The focus of this review is to provide an overview of plant secondary metabolites which act either as insect juvenile hormone (JH) mimics or interfere with JH biosynthesis. Juvenile hormones are sesquiterpenoids which are involved in the regulation of developmental processes such as metamorphosis and reproduction in most insect species [ 5 ]. The first section of this review provides an overview of insect JHs, including their physiological action and biosynthesis in hemimetabolous insects such as the cockroach, Diploptera punctata , and their general chemistry. In the next part, examples of phytochemicals which act as JH mimics (juvenoids) or which inhibit JH biosynthesis will be presented, illustrating the diversity of compounds which are able to interfere with the endocrine system of the insect. Finally, a unique example of the production of insect juvenile hormone III (JH III), methyl-10 R ,11-epoxy-3,7,11-trimethyl 2 E ,6 E -dodecadienoate, in the sedge Cyperus iria L. will be presented and the possible biological role(s) of this compound discussed.
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biosynthetic pathway of insect juvenile hormone iii in cell suspension cultures of the sedge Cyperus iria
Plant Physiology, 2001Co-Authors: Jacqueline C Bede, Walter G Goodman, P. Teal, Stephen S TobeAbstract:In most insect species, juvenile hormones regulate critical physiological processes such as metamorphosis and reproduction. In insects, these sesquiterpenoids are synthesized by retrocerebral endocrine organs, the corpora allata, via the classical mevalonate (MVA) pathway. One of these compounds, juvenile hormone III (JH III), has also been identified in the sedge Cyperus iria . In higher plants, biosynthesis of the sesquiterpenoid backbone may proceed through two distinct pathways: the MVA pathway or the 2 C -methyl erythritol 4-phosphate pathway or through a combination of both pathways. Cell suspension cultures of C. iria were used to elucidate the biosynthetic pathway of JH III in the plant. Enzyme inhibition and labeling studies conclusively demonstrated that the biosynthesis of the sesquiterpenoid backbone of JH III proceeds via the MVA pathway. Inhibitor and precursor feeding studies also suggest that later steps of JH III biosynthesis in C. iria are similar to the insect pathway and that the final enzymatic reaction in JH III biosynthesis is catalyzed by a cytochrome P 450 monooxygenase.
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Activity of insect juvenile hormone III: seed germination and seedling growth studies
CHEMOECOLOGY, 2000Co-Authors: Jacqueline C Bede, Stephen S TobeAbstract:Juvenile hormones are sesquiterpenoids that regulate developmental processses such as metamorphosis and reproduction in insects. Insect juvenile hormone III (JH III), methyl-10 R ,11-epoxy-3,7,11-trimethyl-2 E ,6 E -dodecadienoate, has also been identified in two sedge species, Cyperus iria and C. aromaticus (Toong et al. 1988). Potential allelopathic activity of this compound and the structurally related sesquiterpenoid farnesol was investigated using seed germination and seedling growth assays with radish, lettuce and rice. Treatment of seeds with JH III delayed lettuce seed germination and potently inhibited rice shoot growth. Both farnesol and JH III inhibited the growth of C. iria seedlings. The antimicrobial activity of JH III was also tested on a taxonomic and ecologically diverse range of fungi. Using the classic cytotoxic disk assay, JH III did not effect growth of the fungal species tested. We believe that JH III may contribute to the aggressive nature of this invasive weed species.
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quantification of juvenile hormone iii in the sedge Cyperus iria l comparison of hplc and radioimmunoassay
Phytochemical Analysis, 2000Co-Authors: Jacqueline C Bede, Walter G Goodman, Stephen S TobeAbstract:Juvenile hormone III (JH III), a sesquiterpenoid involved in the regulation of insect development and reproduction, appears to be ubiquitous in insects and has also been isolated from some species of sedge. The quantification of JH III extracted from the sedge Cyperus iria by HPLC and by radioimmunoassay (RIA) has been compared. The RIA, developed originally to determine insect haemolymph titres, was optimized for the analysis of plant tissues. The antiserum 31867 displayed minimal cross-reactivity with precursors of JH III from the insect biosynthetic pathway or with extracts from related plant species. Analysis of standards and plant extracts by HPLC and RIA confirmed that there was no significant difference between the ability of these two techniques to quantify JH III (paired t-test). Therefore, RIA was subsequently used to determine the distribution of JH III in mature plants of C. iria. Substantial concentrations were detected in the above-ground plant tissues (0.2–1.2 µg/g fresh weight), but the majority of JH III was found in the roots (43.5 µg/g fresh weight). Copyright © 2000 John Wiley & Sons, Ltd.
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developmental distribution of insect juvenile hormone iii in the sedge Cyperus iria l
Phytochemistry, 1999Co-Authors: Jacqueline C Bede, Walter G Goodman, Stephen S TobeAbstract:Abstract In insects, juvenile hormones (JHs) regulate physiological processes such as metamorphosis and reproduction but their presence in plants is poorly understood. The temporal and tissue distribution of insect juvenile hormone III (JH III), methyl-10 R ,11-epoxy-3,7,11-trimethyl 2 E ,6 E -dodecadienoate, was determined in sedge ( Cyperus iria L.) over an eight month developmental time course, from the seedling to the senescent plant. Juvenile hormone III levels increased in immature plants until flowering, at which time cessation of plant growth and a transient decrease in JH III content was observed. In mature plants, JH III levels in all plant tissues again increased. In older plants, JH III levels in aerial tissues declined as they became senescent. This decrease was not observed in root tissues which remained viable over the duration of the time course. Moreover, 85% of the total JH III in the plant was present in the roots, suggesting that they are a site of synthesis and/or storage.
Jacqueline C Bede - One of the best experts on this subject based on the ideXlab platform.
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Insect Juvenile Hormones in Plants
Studies in natural products chemistry, 2020Co-Authors: Jacqueline C Bede, Stephen S TobeAbstract:Abstract In the defence against insect herbivory, plants may produce compounds which interfere with the insect endocrine system [ 2, 3, 4 ]. The focus of this review is to provide an overview of plant secondary metabolites which act either as insect juvenile hormone (JH) mimics or interfere with JH biosynthesis. Juvenile hormones are sesquiterpenoids which are involved in the regulation of developmental processes such as metamorphosis and reproduction in most insect species [ 5 ]. The first section of this review provides an overview of insect JHs, including their physiological action and biosynthesis in hemimetabolous insects such as the cockroach, Diploptera punctata , and their general chemistry. In the next part, examples of phytochemicals which act as JH mimics (juvenoids) or which inhibit JH biosynthesis will be presented, illustrating the diversity of compounds which are able to interfere with the endocrine system of the insect. Finally, a unique example of the production of insect juvenile hormone III (JH III), methyl-10 R ,11-epoxy-3,7,11-trimethyl 2 E ,6 E -dodecadienoate, in the sedge Cyperus iria L. will be presented and the possible biological role(s) of this compound discussed.
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biosynthetic pathway of insect juvenile hormone iii in cell suspension cultures of the sedge Cyperus iria
Plant Physiology, 2001Co-Authors: Jacqueline C Bede, Walter G Goodman, P. Teal, Stephen S TobeAbstract:In most insect species, juvenile hormones regulate critical physiological processes such as metamorphosis and reproduction. In insects, these sesquiterpenoids are synthesized by retrocerebral endocrine organs, the corpora allata, via the classical mevalonate (MVA) pathway. One of these compounds, juvenile hormone III (JH III), has also been identified in the sedge Cyperus iria . In higher plants, biosynthesis of the sesquiterpenoid backbone may proceed through two distinct pathways: the MVA pathway or the 2 C -methyl erythritol 4-phosphate pathway or through a combination of both pathways. Cell suspension cultures of C. iria were used to elucidate the biosynthetic pathway of JH III in the plant. Enzyme inhibition and labeling studies conclusively demonstrated that the biosynthesis of the sesquiterpenoid backbone of JH III proceeds via the MVA pathway. Inhibitor and precursor feeding studies also suggest that later steps of JH III biosynthesis in C. iria are similar to the insect pathway and that the final enzymatic reaction in JH III biosynthesis is catalyzed by a cytochrome P 450 monooxygenase.
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Activity of insect juvenile hormone III: seed germination and seedling growth studies
CHEMOECOLOGY, 2000Co-Authors: Jacqueline C Bede, Stephen S TobeAbstract:Juvenile hormones are sesquiterpenoids that regulate developmental processses such as metamorphosis and reproduction in insects. Insect juvenile hormone III (JH III), methyl-10 R ,11-epoxy-3,7,11-trimethyl-2 E ,6 E -dodecadienoate, has also been identified in two sedge species, Cyperus iria and C. aromaticus (Toong et al. 1988). Potential allelopathic activity of this compound and the structurally related sesquiterpenoid farnesol was investigated using seed germination and seedling growth assays with radish, lettuce and rice. Treatment of seeds with JH III delayed lettuce seed germination and potently inhibited rice shoot growth. Both farnesol and JH III inhibited the growth of C. iria seedlings. The antimicrobial activity of JH III was also tested on a taxonomic and ecologically diverse range of fungi. Using the classic cytotoxic disk assay, JH III did not effect growth of the fungal species tested. We believe that JH III may contribute to the aggressive nature of this invasive weed species.
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quantification of juvenile hormone iii in the sedge Cyperus iria l comparison of hplc and radioimmunoassay
Phytochemical Analysis, 2000Co-Authors: Jacqueline C Bede, Walter G Goodman, Stephen S TobeAbstract:Juvenile hormone III (JH III), a sesquiterpenoid involved in the regulation of insect development and reproduction, appears to be ubiquitous in insects and has also been isolated from some species of sedge. The quantification of JH III extracted from the sedge Cyperus iria by HPLC and by radioimmunoassay (RIA) has been compared. The RIA, developed originally to determine insect haemolymph titres, was optimized for the analysis of plant tissues. The antiserum 31867 displayed minimal cross-reactivity with precursors of JH III from the insect biosynthetic pathway or with extracts from related plant species. Analysis of standards and plant extracts by HPLC and RIA confirmed that there was no significant difference between the ability of these two techniques to quantify JH III (paired t-test). Therefore, RIA was subsequently used to determine the distribution of JH III in mature plants of C. iria. Substantial concentrations were detected in the above-ground plant tissues (0.2–1.2 µg/g fresh weight), but the majority of JH III was found in the roots (43.5 µg/g fresh weight). Copyright © 2000 John Wiley & Sons, Ltd.
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developmental distribution of insect juvenile hormone iii in the sedge Cyperus iria l
Phytochemistry, 1999Co-Authors: Jacqueline C Bede, Walter G Goodman, Stephen S TobeAbstract:Abstract In insects, juvenile hormones (JHs) regulate physiological processes such as metamorphosis and reproduction but their presence in plants is poorly understood. The temporal and tissue distribution of insect juvenile hormone III (JH III), methyl-10 R ,11-epoxy-3,7,11-trimethyl 2 E ,6 E -dodecadienoate, was determined in sedge ( Cyperus iria L.) over an eight month developmental time course, from the seedling to the senescent plant. Juvenile hormone III levels increased in immature plants until flowering, at which time cessation of plant growth and a transient decrease in JH III content was observed. In mature plants, JH III levels in all plant tissues again increased. In older plants, JH III levels in aerial tissues declined as they became senescent. This decrease was not observed in root tissues which remained viable over the duration of the time course. Moreover, 85% of the total JH III in the plant was present in the roots, suggesting that they are a site of synthesis and/or storage.
Robert C Scott - One of the best experts on this subject based on the ideXlab platform.
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Acetolactate Synthase–Inhibiting, Herbicide-Resistant Rice Flatsedge (Cyperus iria): Cross-Resistance and Molecular Mechanism of Resistance
Weed Science, 2020Co-Authors: Dilpreet S Riar, Parsa Tehranchian, Jason K Norsworthy, Vijay K Nandula, Scott Mcelroy, Vibha Srivastava, Shu Chen, Jason A Bond, Robert C ScottAbstract:Abstract Overuse of acetolactate synthase (ALS)–inhibiting herbicides in rice has led to the evolution of halosulfuron-resistant rice flatsedge in Arkansas and Mississippi. Resistant accessions were cross-resistant to labeled field rates of ALS-inhibiting herbicides from four different families, in comparison to a susceptible (SUS) biotype. Resistance index of Arkansas and Mississippi accessions based on an R/S ratio of the lethal dose required for 50% plant mortality (LD50) to bispyribac-sodium, halosulfuron, imazamox, and penoxsulam was ≥ 21-fold. Control of Arkansas, Mississippi, and SUS accessions with labeled field rates of 2,4-D, bentazon, and propanil was ≥ 93%. An enzyme assay revealed that an R/S ratio for 50% inhibition (I50) of ALS for halosulfuron was 2,600 and 200 in Arkansas and Mississippi, respectively. Malathion studies did not reveal enhanced herbicide metabolism in resistant plants. The ALS enzyme assay and cross-resistance studies point toward altered a target site as the potential mec...
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acetolactate synthase inhibiting herbicide resistant rice flatsedge Cyperus iria cross resistance and molecular mechanism of resistance
Weed Science, 2015Co-Authors: Dilpreet S Riar, Parsa Tehranchian, Jason K Norsworthy, Vijay K Nandula, Scott Mcelroy, Vibha Srivastava, Shu Chen, Jason A Bond, Robert C ScottAbstract:Abstract Overuse of acetolactate synthase (ALS)–inhibiting herbicides in rice has led to the evolution of halosulfuron-resistant rice flatsedge in Arkansas and Mississippi. Resistant accessions were cross-resistant to labeled field rates of ALS-inhibiting herbicides from four different families, in comparison to a susceptible (SUS) biotype. Resistance index of Arkansas and Mississippi accessions based on an R/S ratio of the lethal dose required for 50% plant mortality (LD50) to bispyribac-sodium, halosulfuron, imazamox, and penoxsulam was ≥ 21-fold. Control of Arkansas, Mississippi, and SUS accessions with labeled field rates of 2,4-D, bentazon, and propanil was ≥ 93%. An enzyme assay revealed that an R/S ratio for 50% inhibition (I50) of ALS for halosulfuron was 2,600 and 200 in Arkansas and Mississippi, respectively. Malathion studies did not reveal enhanced herbicide metabolism in resistant plants. The ALS enzyme assay and cross-resistance studies point toward altered a target site as the potential mec...
David E Johnson - One of the best experts on this subject based on the ideXlab platform.
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responses of rice flatsedge Cyperus iria and barnyardgrass echinochloa crus galli to rice interference
Weed Science, 2010Co-Authors: Bhagirath S Chauhan, David E JohnsonAbstract:Abstract Rice flatsedge and barnyardgrass are widespread and competitive weeds in direct-seeded rice. Developing integrated weed management strategies that elevate suppression of weeds by rice through crop density, nutrition, and cultivar choice requires better understanding of the extent to which rice interferes with the growth of these weeds and how these species respond to resource limitation with crop interference. Rice interference reduced the height of barnyardgrass but did not affect height of rice flatsedge. These weed species were able to grow taller than rice and thus avoided being shaded. Increased specific stem length under crop interference may demonstrate a strategy of stem elongation to allow the top portion of the weeds to be kept out of shade. Rice interference reduced inflorescence and shoot biomass of both weed species. Barnyardgrass showed the ability to reduce the effects of rice interference by increasing leaf weight ratio. The present study shows that crop interference alone may red...
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ecological studies on Cyperus difformis Cyperus iria and fimbristylis miliacea three troublesome annual sedge weeds of rice
Annals of Applied Biology, 2009Co-Authors: Bhagirath S Chauhan, David E JohnsonAbstract:Cyperus difformis, Cyperus iria and Fimbristylis miliacea are troublesome annual sedges of rice grown in many countries. Laboratory and screenhouse experiments were conducted to determine the effects of temperature, light, salt and water stress, seed burial depth, and flooding time, duration and depth on germination, emergence and growth of these three species. Germination of all the three species was stimulated by light and warm fluctuating temperatures. Germination of C. difformis was influenced to a greater degree by increasing salt and water stress than C. iria and F. miliacea. In all three species, seeds sown on the soil surface gave the greatest percentage of seedling emergence, and no seedlings emerged from seeds buried in soil at depths of ≥1 cm. Flooding, although not continuous or deep, had a suppressive effect on emergence and growth of C. iria and F. miliacea. Intermittent flooding to shallow depths, however, was less effective in controlling C. difformis; deep flooding was needed to suppress growth of C. difformis seedlings. When the flooding was delayed to 21 days after sowing, there was little growth reduction in all three species.
Bhagirath S Chauhan - One of the best experts on this subject based on the ideXlab platform.
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growth analysis and biomass partitioning of Cyperus iria in response to rice planting density and nitrogen rate
Crop Protection, 2015Co-Authors: Pompe Sta C Cruz, Tahir Hussain Awan, Bhagirath S ChauhanAbstract:Cyperus iria is a weed of rice with widespread occurrence throughout the world. Because of concerns about excessive and injudicious use of herbicides, cultural weed management approaches that are safe and economical are needed. Developing such approaches will require a better understanding of weed biology and ecology, as well as of weed response to increases in crop density and nutrition. Knowledge of the effects of nitrogen (N) fertilizer on crop-weed competitive interactions could also help in the development of integrated weed management strategies. The present study was conducted in a screenhouse to determine the effects of rice planting density (0, 5, 10, and 20 plants pot−1) and N rate (0, 50, 100, and 150 kg ha−1) on the growth of C. iria. Tiller number per plant decreased by 73–88%, leaf number by 85–94%, leaf area by 85–98%, leaf biomass by 92–99%, and inflorescence biomass by 96–99% when weed plants were grown at 20 rice plants pot−1 (i.e., 400 plants m−2) compared with weed plants grown alone. All of these parameters increased when N rates were increased. On average, weed biomass increased by 118–389% and rice biomass by 121–275% with application of 50–150 kg N ha−1, compared to control. Addition of N favored weed biomass production relative to rice biomass. Increased N rates reduced the root-to-shoot weight ratio of C. iria. Rice interference reduced weed growth and biomass and completely suppressed C. iria when no N was applied at high planting densities (i.e., 20 plants pot−1). The weed showed phenotypic plasticity in response to N application, and the addition of N increased the competitive ability of the weed over rice at densities of 5 and 10 rice plants pot−1 compared with 20 plants pot−1. The results of the present study suggest that high rice density (i.e., 400 plants m−2) can help suppress C. iria growth even at high N rates (150 kg ha−1).
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responses of rice flatsedge Cyperus iria and barnyardgrass echinochloa crus galli to rice interference
Weed Science, 2010Co-Authors: Bhagirath S Chauhan, David E JohnsonAbstract:Abstract Rice flatsedge and barnyardgrass are widespread and competitive weeds in direct-seeded rice. Developing integrated weed management strategies that elevate suppression of weeds by rice through crop density, nutrition, and cultivar choice requires better understanding of the extent to which rice interferes with the growth of these weeds and how these species respond to resource limitation with crop interference. Rice interference reduced the height of barnyardgrass but did not affect height of rice flatsedge. These weed species were able to grow taller than rice and thus avoided being shaded. Increased specific stem length under crop interference may demonstrate a strategy of stem elongation to allow the top portion of the weeds to be kept out of shade. Rice interference reduced inflorescence and shoot biomass of both weed species. Barnyardgrass showed the ability to reduce the effects of rice interference by increasing leaf weight ratio. The present study shows that crop interference alone may red...
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ecological studies on Cyperus difformis Cyperus iria and fimbristylis miliacea three troublesome annual sedge weeds of rice
Annals of Applied Biology, 2009Co-Authors: Bhagirath S Chauhan, David E JohnsonAbstract:Cyperus difformis, Cyperus iria and Fimbristylis miliacea are troublesome annual sedges of rice grown in many countries. Laboratory and screenhouse experiments were conducted to determine the effects of temperature, light, salt and water stress, seed burial depth, and flooding time, duration and depth on germination, emergence and growth of these three species. Germination of all the three species was stimulated by light and warm fluctuating temperatures. Germination of C. difformis was influenced to a greater degree by increasing salt and water stress than C. iria and F. miliacea. In all three species, seeds sown on the soil surface gave the greatest percentage of seedling emergence, and no seedlings emerged from seeds buried in soil at depths of ≥1 cm. Flooding, although not continuous or deep, had a suppressive effect on emergence and growth of C. iria and F. miliacea. Intermittent flooding to shallow depths, however, was less effective in controlling C. difformis; deep flooding was needed to suppress growth of C. difformis seedlings. When the flooding was delayed to 21 days after sowing, there was little growth reduction in all three species.
