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1
Villari, Caterina. « Fungi associated with the pine engraver beetle Ips acuminatus and their interactions with the host tree ». Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3422532.
Texte intégralRésumé :
Conifer bark beetles are typically associated with complexes of fungi with which they can display different functional relationships. Some of the fungi, generally non phytopathogenic, are known to have a directly mutualistic interaction with the beetles, serving as nourishment to the larvae. Other associated fungi are thought to be involved in the process of exhausting plant defenses, which is a necessary step for the insects to overcome host tree resistance and colonize the plant. In the latter case, bark beetle-associated fungi are often tree pathogenic species belonging to the morphologically homogenous group of the ophiostomatoid fungi, also referred to as ‘blue-stain’ fungi. In spite of the great interest the bark beetle-fungi symbiosis has gained in time, many fundamental aspects of this relationship are still widely debated, as for instance the degree of dependence of bark beetles on the blue-stain fungi in order to succeed their establishment in the host plant.
In this thesis I addressed the fungal community associated with the pine engraver beetle Ips acuminatus (Gyll.), a small bark beetle infesting thin bark of Scots pine (Pinus sylvestris L.) and that has been recently reported as pest in many alpine forests. I. acuminatus associated fungal community includes the obligate nutritional fungus Hyalorhinocladiella macrospora (Franke-Grosm.) Harr. and a specific blue-stain fungus which is consistently associated with the vector, but which identity is still uncertain. Early reports describe it as Ophiostoma clavatum Math.-Käärik, while a later research reported O. brunneo-ciliatum Math. instead. Objectives of the thesis were to determine the identity of the blue-stain fungi associated with I. acuminatus, and to investigate the fungal community interactions with the host plant, in order to better define the functional relationships occurring between the bark beetle and the associated fungi, and therefore contribute to the attempts in understanding ecology and population dynamics of this damaging species.
In the first work a blue-stain fungus associated with I. acuminatus specimens collected in Italy and Sweden was isolated and identified. The identification of the species was achieved with both the support of morphological methods and DNA sequence-based methods, and the species resulted to be O. clavatum, in agreement with the first researches focused on I. acuminatus associated fungi.
In the second work, to clearly assess which of the previously described Ophiostoma species was the main blue-stain fungus associated with the pine engraver beetle, three loop-mediated isothermal amplification (LAMP) assays were developed and employed in a survey which has covered six Italian populations of I. acuminatus. The results confirmed that the identity of the blue-stain fungus more consistently associated with I. acuminatus in the Italian Alps is O. clavatum, while O. brunneo-ciliatum was not detected in any of the samples. Results of this study showed also that the occurrence of O. clavatum varies accordingly to the population dynamic phase of the vector, and is slightly lower in the outbreak populations.
In the third work, the local and systemic defense responses of Scots pine against both the nutritional and the blue-stain fungi were characterized by identifying and quantifying terpenoids, phenolic compounds, and lignin. Results indicated that Scots pine has a generic, rather than specific, induced response. The fact that the nutritional and the blue-stain fungi triggered comparable induced defense responses suggests that even a non-pathogenic fungus may participate in exhausting host plant defenses, indirectly assisting in the beetle establishment process. This finding contributes to the further development of current theories on the role of associated fungal complexes in bark beetle ecology.
In the last work, correlation patterns within constitutive defense secondary metabolites of Scots pine and potential trade-offs between constitutive concentration and inducible variation of individual chemical compounds were tested. Results revealed that different compounds display different behaviors, but no overall negative associations between defensive traits were found.
On the whole, the four contributions of this thesis provide suggestions for a revaluation of one of the current theories on the role of associated fungi in bark beetles host establishment, and hints to understand the role of associated fungi in the population dynamics of bark beetles. Moreover, they clarify some aspects of Scots pine defense mechanisms, highlighting its competitiveness.Gli scolitidi delle conifere sono insetti spesso associati ad un complesso di funghi con i quali possono instaurare differenti interazioni ecologiche. Alcuni di questi funghi, generalmente non fitopatogeni, sono coinvolti in un’interazione mutualistica diretta e vengono utilizzati come nutrimento per le larve del vettore. Altri funghi associati, invece, sono ritenuti coinvolti nel processo di esaurimento delle difese della pianta, che per l’insetto è uno dei passaggi necessari per superare la resistenza dell’ospite e poterlo quindi colonizzare. In quest’ultimo caso, i funghi associati sono di norma specie patogene appartenenti al gruppo morfologico dei funghi ophiostomatoidi, noti anche come ‘funghi di azzurramento’. Nonostante l’interesse che la simbiosi tra scolitidi e funghi ha riscosso nel tempo, molti degli aspetti fondamentali di questa interazione sono ancora discussi, come ad esempio il grado di dipendenza degli insetti vettori dai loro simbionti nelle fasi di colonizzazione della pianta ospite. In questa tesi è stata presa in considerazione la comunità fungina associata a Ips acuminatus (Gyll.), un piccolo scolitide che attacca di preferenza le parti del tronco del pino silvestre (Pinus sylvestris L.) con corteccia sottile, e che di recente ha causato numerose infestazioni in varie zone distribuite sull’arco alpino. Una delle specie che fanno parte della comunità fungina associata ad I. acuminatus è il simbionte alimentare Hyalorhinocladiella macrospora (Franke-Grosm.) Harr. Fa inoltre parte del complesso anche uno specifico fungo di azzurramento costantemente associato al vettore, ma la cui identità non è ancora ben definita. Le prime segnalazioni lo descrivono come Ophiostoma clavatum Math.-Käärik, mentre ricerche successive riportano O. brunneo-ciliatum Math. Gli obiettivi che questa tesi si è prefissa sono stati determinare l’effettiva identità del fungo di azzurramento associato ad I. acuminatus, ed indagare le interazioni del complesso fungino con la pianta ospite, al fine di definire meglio le relazioni che intercorrono tra scolitidi e fungi associati, e poter quindi contribuire ai tentativi di chiarire l’ecologia e la dinamica di popolazione di questo insetto dannoso. Nel primo lavoro sono stati descritti l’isolamento e l’identificazione di una specie fungina isolata da individui di I. acuminatus raccolti in Italia e in Svezia. L’identificazione della specie è avvenuta sia grazie all’osservazione delle caratteristiche morfologiche sia mediante un approccio di tipo molecolare. La specie è risultata essere O. clavatum, come era stato indicato nelle prime segnalazioni riguardanti i funghi associati ad I. acuminatus. Nel secondo lavoro sono stati descritti la messa punto e l’utilizzo di tre sonde molecolari per loop-mediated isothermal amplification (LAMP), con l’obiettivo di determinare quale delle due specie del genere Ophiostoma sopracitate fosse effettivamente il fungo maggiormente associato a I. acuminatus nell’arco alpino. I risultati, riguardanti sei popolazioni italiane dell’insetto, hanno confermato che la specie maggiormente presente è O. clavatum, mentre O. brunneo-ciliatum non è mai stata rilevata. I risultati di questo studio hanno mostrato anche che la frequenza di associazione di I. acuminatus con O. clavatum varia a seconda della fase epidemica, ed è minore nei nuclei di infestazione rispetto alle popolazioni endemiche. Nel terzo lavoro sono state caratterizzate le risposte sia locali sia sistemiche del pino silvestre alla colonizzazione da parte del simbionte alimentare e del fungo di azzurramento, identificando e quantificando alcuni metaboliti secondari, come terpeni, fenoli e lignina. I risultati hanno mostrato che il pino silvestre risponde in maniera generica anziché specifica all’induzione. Il fatto inoltre che il simbionte alimentare e il fungo di azzurramento abbiano stimolato una risposta simile di loro suggerisce che anche un fungo non patogeno possa partecipare al processo di esaurimento delle difese della pianta, assistendo quindi l’insetto nelle fasi di colonizzazione dell’ospite. Questo risultato contribuisce quindi allo sviluppo delle attuali teorie sul ruolo dei funghi associati nell’ecologia degli scolitidi. Nell’ultimo lavoro sono state studiate le correlazioni tra i metaboliti secondari delle difese costitutive del pino silvestre, e le correlazioni tra la concentrazione costitutiva e la variazione indotta dei singoli composti. I risultati hanno messo in evidenza una differenziazione di comportamento tra composti e l’assenza in generale di una correlazione inversa tra i tipi diversi di difese, al contrario di quanto previsto da alcune teorie. Nel complesso, i quattro contributi di questa tesi suggeriscono la rivalutazione di una delle attuali teorie sul ruolo dei funghi associati nella colonizzazione dell’ospite da parte degli scolitidi, e forniscono degli spunti per la comprensione del ruolo dei funghi associati nella dinamica di popolazione del vettore. Chiariscono inoltre alcuni degli aspetti dei meccanismi di difesa del pino silvestre, mettendo in evidenza la sua competitività.
2
Sinclair, Steven J. « QPRTase : a wound-induced defence gene in Nicotiana ». Monash University, School of Biological Sciences, 2003. http://arrow.monash.edu.au/hdl/1959.1/6571.
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3
Warner, Simon A. J. « Cloning and characterization of an asparagus wound-induced gene ». Thesis, University of Leicester, 1992. http://hdl.handle.net/2381/35363.
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Following previous studies, Asparagus officinalis single cell suspensions were hypothesized to be a rich source of wound-inducible mRNAs. A previously isolated clone, DDl-34, was shown to hybridize to wound-inducible transcript. This sequence was used to isolate the AoPR1 (Asparagus officinalis Pathogenesis Related cDNA clone 1). Data from the isolation and analysis of genomic clones hybridizing to DDl-34 probe suggested that these clones were unlikely to contain the upstream regulatory sequences of the AoPR1 gene and that the genomic arrangement of these sequences is complex. Inverse polymerase chain reactions (IPCR) were used to amplify AoPR1 genic sequences directly from the asparagus genome. Two products were cloned and sequenced, demonstrating that the correct sequences, upstream and downstream of the primers, had been amplified. The downstream IPCR product's sequence overlaps with AoPR1 coding sequence and contains an intron sequence. The upstream IPCR product partially overlaps with the start of AoPR1 coding sequence and was successfully used in transcript mapping experiments. Translational fusions were constructed between this fragment and the -glucuronidase (gus) reporter gene. GUS analysis demonstrated that this fragment, containing the AoPR1 promoter, was sufficient to drive wound-inducible transcription in transgenic tobacco. A smaller upstream fragment was insufficient to drive wound-inducible transcription. GUS expression was also detectable in tissues such as the xylem parenchyma, mature pollen and coloured regions of the petal. AoPR1-gus transgene expression correlates with the spatial expression patterns of phenylpropanoid biosynthesis pathway genes. The nature of the fusion suggested that the AoPR1 protein is intracellular. This is the first example of the cloning and analysis of a monocotyledon gene belonging to the 'intracellular pathogenesis related protein' class. The analysis and application of AoPR1 sequences are discussed.
4
Venkatasubramaniam, Shyam. « Constitutive Modeling of Poly(Ethylene Terephthalate) ». The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417444300.
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5
Singh, Jasber. « The plasma membrane Hâº-TPase and pathogen-induced plant defence ». Thesis, Lancaster University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423560.
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6
Tang, M. « Elicitor-induced defence response and signal mechanisms in Medicago sativa L ». Thesis, Swansea University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639158.
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In this study, the responses and signal mechanisms were explored with a model system, concerning the interactions between lucerne suspension cells (Medicago sativa L., cv. Kabul) and elicitor either from avirulent (V2) or virulent (V1) isolate of Verticillium, alboatrum. V2 elicitor induced a two-phase of H2O2 accumulation in the cell cultures. Activation of defence expression led to an increase in PAL activity, phytoalexin accumulation and deposition of phenolic polymers. However, activities of antioxidant enzymes, such as catalase, peroxidases, glucanase, glutathione reductase, did not show obvious increase within 24 h after treatment with the elicitor. Glutathione S-transferase activity increased after 1st oxidative burst. V1 elicitor induced similar defence responses as V2 did, but a stronger response was observed when the same concentration of elicitor was used, confirming that Kabul is a resistance cultivar to V. albo-atrum. Ca2+ influx is necessary for oxidative burst, PAL activity and phytoalexin accumulation. Either blocking Ca2+ channel by La3+ or reduction of extracellular Ca2+ amount by EGTA, had an important inhibition on oxidative burst, PAL activity and phytoalexin accumulation. Intracellular Ca2+ also played a role in downstream signalling. Intracellular Ca2+ inhibitors. TBM-8 and Ruthenium red, strongly inhibited the PAL activity and phytoalexin accumulation. Oxidative burst has a relation with defence expression. An NADPH oxidase inhibitor, diphenyleneiodonium (DPI), which inhibited oxidative burst effectively, also inhibited PAL activity and phytoalexin accumulation. However, DCN, an inhibitor of peroxidase, also inhibited and oxidative burst, PAL activity and phytoalexin accumulated in micromolar range. Oxidative burst with superoxide-origin is related to defence activation. The H2O2 itself did not stimulate an activation of PAL activity. Addition of superoxide dismutase (SOD) stimulated an increase in H2O2 accumulation. Microsomal membranes are capable of superoxide synthesis when NADPH/NADH was used as electron donor, which was DPI-sensitive. This enzyme activity increased after treatment of the cell cultures with elicitor.
7
Stirrup, Timothy J. « Induced defence in wild cabbage : integrating genes, volatiles & ; insect behaviour ». Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439371.
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8
Gibberd, R. M. « Wound-induced plant responses and their consequences for insect grazing ». Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378189.
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Dean, Edward Timothy Richard. « An isotropic transformations soil constitutive model with induced anisotropy in axial deformation events ». Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293200.
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Bechtold, David Alexander. « Localization of constitutive and hyperthermia-induced heat shock proteins to synapses of the rat brain ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0026/MQ50477.pdf.
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SOMASUNDARAM, SUJITHAN. « CONSTITUTIVE MODELLING FOR ANISOTROPIC HARDENING BEHAVIOR WITH APPLICATIONS TO COHESIONLESS SOILS (INDUCED, KINEMATIC, NON-ASSOCIATIVENESS) ». Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/188165.
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A constitutive model based on rate-independent elastoplasticity concepts is developed to simulate the behavior of geologic materials under arbitrary three-dimensional stress paths, stress reversals and cyclic loading. The model accounts for the various factors such as friction, stress path, stress history, induced anisotropy and initial anisotropy that influence the behavior of geologic materials. A hierarchical approach is adapted whereby models of progressively increasing sophistication are developed from a basic isotropic-hardening associative model. The influence of the above factors is captured by modifying the basic model for anisotropic (kinematic) hardening and deviation from normality (nonassociativeness). Both anisotropic hardening and deviation from normality are incorporated by introducing into the formulation a second order tensor whose evolution is governed by the level of induced anisotropy in the material. In the stress-space this formulation may be interpreted as a translating potential surface Q that moves in a fixed field of isotropic yield surfaces. The location of the translating surface in the stress-space, at any stage of the deformation, is given by the 'induced anisotropy' tensor. A measure to represent the level of induced anisotropy in the material is defined. The validity of this representation is investigated based on a series of special stress path tests in the cubical triaxial device on samples of Leighton Buzzard sand. The significant parameters of the models are defined and determined for three sands based on results of conventional laboratory test results. The model is verified with respect to laboratory multiaxial test data under various paths of loading, unloading, reloading and cyclic loading.
12
Brändli, Peter Richard. « Disorders of regulated and constitutive secretion in pituitary thyrotrophs of streptozotocin-induced diabetic male rats / ». [S.l.] : [s.n.], 1992. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Beilke, Lisa D. « Mechanisms of Hepatoprotection in a Murine Model of Bile Acid-Induced Intrahepatic Cholestasis ». Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/194264.
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There are many causes of cholestasis, which results when the flow of bile acids is slowed or stopped. Bile acids are hydrophobic molecules synthesized from cholesterol in the liver, and when present in excess, are cytotoxic to cell membranes. Treatment options for cholestasis are limited, and if left untreated or inadequately treated, many patients will require a liver transplant; thus, underscoring the importance of successfully managing this disease. Activation of nuclear receptors in animal models has been shown to be hepatoprotective during bile acid-induced cholestasis; however, the mechanisms underlying the hepatoprotective effects are poorly understood. Therefore, the over-arching goal of this project is to glean an improved comprehension of the mechanisms of hepatoprotection during bile acid-induced cholestasis. All of the studies involve administration of CAR activators phenobarbital (PB), oltipraz (OPZ), 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene [TCPOBOP (TC)] or corn oil (CO) to C57BL/6 wild type (WT), or WT and CAR knockout (CAR-/-) mice prior to induction of intrahepatic cholestasis using the secondary bile acid lithocholic acid (LCA). Efflux transport proteins such as Mrps 3 and 4 are known to be up-regulated during cholestasis, and this was the first topic of exploration. Unexpectedly, the expression of efflux transporters was not consistently up-regulated in protected mice. However, a decrease in total liver bile acid concentrations was observed. These changes in hepatic bile acids indicated that bile acid biosynthesis may be relevant to hepatoprotection. Indeed decreases in total and individual bile acids correlated with hepatoprotection, and Cyp8b1 expression was also increased which could be suggestive of a shift in the bile acid biosynthesis pathway towards the formation of less toxic bile acid species. CAR may also have a role in cell death via apoptosis by altering Bcl-2 protein expression. Although apoptosis was decreased in hepatoprotected mice, an increase in the expression of Mcl-1 and Bcl-xL was not observed, suggesting hepatoprotection is not a direct result of CAR-induced Mcl-1 expression. These findings add significantly to the body of knowledge surrounding cholestatic liver disease and suggest that studies aimed toward manipulation of nuclear receptors are worthy of further exploration.
14
Berg, Femke van den. « The evolution of plant defence against pests : pathogen development and pathogen-induced leaf necrosis ». Thesis, University of Reading, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421209.
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Najarian, Taline. « Hypercapnia-induced, potassium channel and prostaglandin dependent modulation of endothelial constitutive nitric oxide synthase in neonatal brain ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0034/MQ64414.pdf.
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Brunal-Brown, Alyssa Alexandra. « Effects of constitutive and acute Connexin 36 deficiency on brain-wide susceptibility to PTZ-induced neuronal hyperactivity ». Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/100748.
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Connexins are transmembrane proteins that form hemichannels allowing the exchange of molecules between the extracellular space and the cell interior. Two hemichannels from adjacent cells dock and form a continuous gap junction pore, thereby permitting direct intercellular communication. Connexin 36 (Cx36), expressed primarily in neurons, is involved in the synchronous activity of neurons and may play a role in aberrant synchronous firing, as seen in seizures. To understand the reciprocal interactions between Cx36 and seizure-like neural activity, we examined three questions: a) does Cx36 deficiency affect seizure susceptibility, b) does seizure-like activity affect Cx36 expression patterns, and c) does acute blockade of Cx36 conductance increase seizure susceptibility. We utilize the zebrafish pentylenetetrazol (PTZ; a GABA(A) receptor antagonist) induced seizure model, taking advantage of the compact size and optical translucency of the larval zebrafish brain to assess how PTZ affects brain-wide neuronal activity and Cx36 protein expression. We exposed wild-type and genetic Cx36-deficient (cx35.5-/-) zebrafish larvae to PTZ and subsequently mapped neuronal activity across the whole brain, using phosphorylated extracellular-signal-regulated kinase (pERK) as a proxy for neuronal activity. We found that cx35.5-/- fish exhibited region-specific susceptibility and resistance to PTZ-induced hyperactivity compared to wild-type controls, suggesting that genetic Cx36 deficiency may affect seizure susceptibility in a region-specific manner. Regions that showed increased PTZ sensitivity include the dorsal telencephalon, which is implicated in human epilepsy, and the lateral hypothalamus, which has been underexplored. We also found that PTZ-induced neuronal hyperactivity resulted in a rapid reduction of Cx36 protein levels within. 30 minutes and one-hour exposure to 20 mM PTZ significantly reduced the expression of Cx36. This Cx36 reduction persists after one-hour of recovery but recovered after 3-6 hours. This acute downregulation of Cx36 by PTZ is likely maladaptive, as acute pharmacological blockade of Cx36 by mefloquine results in increased susceptibility to PTZ-induced neuronal hyperactivity. Together, these results demonstrate a reciprocal relationship between Cx36 and seizure-associated neuronal hyperactivity: Cx36 deficiency contributes region-specific susceptibility to neuronal hyperactivity, while neuronal hyperactivity-induced downregulation of Cx36 may increase the risk of future epileptic events.Doctor of Philosophy
Within the brain, cells (neurons) communicate with each other to pass along information. This communication is important for normal functions of the brain such as learning and memory, muscle movement, etc. Epilepsy is a disease of the brain that is caused by rapid over synchronized communication between cells. This leads to seizures which can include convulsions, loss of attention, and much more. Currently, 30% of patients suffering from epilepsy do not have a treatment option that works for them, it is, therefore, imperative to investigate new targets for treatment in this disease. Connexin36 is a protein in the brain that directly connects cells so they can pass information quickly between them. Connexin36, therefore, might make a good target for treatment. Previous work has aimed to understand this relationship but has been limited in their ability to look at the entire brain at any one time. The goal of this study was to understand the relationship between connexin 36 and brain hyperactivity across the whole brain simultaneously. To understand this relationship, we first determined what happened to brain activity if the protein was missing entirely after exposure to a seizure causing drug. We were asking: How does connexin 36 affect hyperactivity. We found that different regions of the brain responded differently without the connexin 36 protein. This suggests that one size does not fit all, and one must look at the whole brain to understand the effects of the connexin 36 protein. Next, we asked a similar question, but in the opposite direction, how does hyperactivity affect connexin 36? We found, in the short-term, hyperactivity reduced the amount of connexin 36 present in certain regions of the brain. This continued until 3 hours following exposure to the seizure causing drug Pentylenetetrazol (PTZ). Lastly, to determine if this short-term reduction in connexin 36 meant that an individual was more likely to experience hyperactivity. To do this, we used a connexin 36 blocking drug, then introduced the seizure causing drug at different concentrations. We found, at all concentrations, the connexin 36 blocking drug caused significant changes in neuronal activity, depending on the brain regions. Overall, our results showed that connexin 36 plays an important role in hyperactivity and that a short-term reduction in connexin 36 is detrimental, and may contribute to an increase in the possibility of subsequent hyperactivity.
17
Copple, Ian Mathew. « The transcriptional regulation of cell defence and its role in protection against drug-induced liver injury ». Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479064.
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Huang, Ping. « Constitutive and TCDD-induced expression of Ah receptor responsive genes with special focus on the brain and pituitary / ». Stockholm, 2003. http://diss.kib.ki.se/2003/91-7349-434-8/.
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Coleman, Ross Antony. « Herbivore behaviour, multitrophic interactions and a lack of wound-induced defence in a member of the Cruciferae ». Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242558.
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Beese, Allison M. « Experimental investigation and constitutive modeling of the large deformation behavior of anisotropic steel sheets undergoing strain-induced phase transformation ». Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67576.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 139-146).
The strain-induced phase transformation from austenite to martensite is responsible for the high strength and ductility of TRansformation-Induced Plasticity (TRIP)- assisted steels. The large deformation behavior of conventional steels is governed by crystallographic slip. In the case of TRIP steels, the phase transformation provides an additional microstructural deformation mechanism, which has a particularly strong effect on the strain hardening response at the macroscopic level. This thesis work develops a new plasticity model for TRIP steels that accounts for the effect of phase transformation. In particular, the large deformation behavior of 1.5mm thick stainless steel 301LN sheets at room temperature is studied in detail. Several techniques for quantifying the martensite volume fraction are evaluated including micrography, X-ray diffraction, neutron diffraction, magnetic saturation, and magnetic permeability measurements. The latter is then used to measure the evolution of the martensite content throughout mechanical experiments. The experimental program for different stress states includes experiments for uniaxial tension, uniaxial compression, equi-biaxial tension, pure shear, and transverse plane strain tension. The resulting experimental data demonstrate the influence of both the stress triaxiality and Lode angle parameter on the austenite-to-martensite transformation kinetics. A stress-state dependent transformation kinetics evolution equation is proposed which describes the martensite content as a function of plastic strain, the stress triaxiality, and the Lode angle parameter. Furthermore, a phenomenological plasticity model is developed comprising an anisotropic yield function, an isotropic hardening law, and a nonlinear kinematic hardening law with initial back stress. The isotropic hardening law expresses the increase in deformation resistances as a function of the plastic strain and the martensite content and is directly coupled with the stress-state dependent transformation kinetics equation. As a result, the model is able to describe the experimentally observed effect of stress state on the macroscopic hardening response. The constitutive model is implemented into a finite element program and used to simulate all experiments performed. The model predictions agree well with the experimental results for a wide range of stress states and for both specimens with homogeneous and heterogeneous stress and strain fields.
by Allison M. Beese.
Ph.D.
21
Kitamura, Jiro. « Chronic Lung Injury by Constitutive Expression of Activation-Induced Cytidine Deaminase Leads to Focal Mucous Cell Metaplasia and Cancer ». Kyoto University, 2015. http://hdl.handle.net/2433/200440.
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Sanmartín, Martínez Neus. « Deciphering mechanisms underlying Mycorrhizal Induced Resistance in tomato plants ». Doctoral thesis, Universitat Jaume I, 2021. http://dx.doi.org/10.6035/14104.2021.722450.
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En esta tesis doctoral he tratado de descifrar algunos de los mecanismos tras la Resistencia Inducida por Micorrizas (MIR).
Las plantas micorrizadas son más sensibles y perciben más rápido un futuro estrés. Esto está acompañado por un reordenamiento metabolómico y una aumentada deposición de callosa dirigida por cambios proteicos tras el establecimiento de la simbiosis. Estas modificaciones pueden ser los mecanismos claves en la MIR frente a Botrytis cinerea. Además, cambios puntuales en los volátiles en plantas micorrizadas también pueden contribuir a la mayor resistencia frente al patógeno al mostrar propiedades antifúngicas.In this doctoral thesis I have tried to decipher some mechanisms behind Mycorrhiza-Induced Resistance (MIR). Mycorrhizal plants become more sensitive and perceive earlier the upcoming stress. This is accompanied by a plant metabolic rearrangement and enhanced callose accumulation directed by protein changes after symbiosis establishment. These modifications can be key components of defence priming behind MIR against Botrytis cinerea. Furthermore, the changes in specific VOCs released by mycorrhizal plants likely contribute to the enhanced resistance since they show antifungal properties.
Programa de Doctorat en Ciències
23
Carlier, Florian. « Fonctions et organisations de l’hétérochromatine au cours du développement sexué chez le champignon filamenteux Podospora anserina ». Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS457/document.
Texte intégralRésumé :
Pour se défendre des effets délétères des éléments transposables, les pezizomycotina ont développé un système de défense génétique et épigénétique appelé « Repeat Induced Point Mutation » (RIP). Chez N. crassa, le RIP survient dans la cellule dicaryotique avant la caryogamie et conduit à la méthylation de novo des cytosines (5mC) inclues dans les séquences répétées de chacun des noyaux parentaux haploïdes. De plus, certaines de ces cytosines sont la cible d’un processus de mutation qui les transforme en thymines. Cette étape est suivie par la mise en place locale de l’hétérochromatine constitutive permettant une répression transcriptionnelle durable des séquences cibles du RIP au cours des divisions nucléaires. L’acteur majeur du RIP correspond à une cytosine méthyltransférase putative appelée RID (RIP Defective). Bien que son génome ne montre pas une quantité significative de 5mC, l’inactivation de PaRid chez Podospora anserina aboutit à un blocage du développement sexué survenant après la fécondation. Dans ce contexte, nous avons voulu déterminer si la fonction de PaRid dans le développement sexué consiste à éteindre l’expression de gènes cibles via l’installation de foyers d’hétérochromatine constitutive aux loci concernés. Pour ce faire, nous avons identifié les gènes PaKmt1 et PaHP1, codant respectivement l’histone méthyltransférase PaKmt1 (l’homologue de SU(VAR)39 qui catalyse la tri-méthylation du résidu H3K9 (H3K9me3) et PaHP1 (l’homologue de Heterochromatin Protein 1 qui se lie à H3K9me3). Les deux protéines interviennent dans une même voie de régulation qui aboutit à la mise en place de l’hétérochromatine constitutive. Par opposition, PaKmt6, homologue de l’histone méthyltransférase E(Z), correspond à la sous-unité catalytique du complexe PRC2 qui catalyse la marque H3K27me3 pour permettre l’établissement de l’hétérochromatine facultative. Nos résultats ont montré que l’absence de PaKmt1 et PaHP1 ne provoquent que des défauts mineurs. A l’inverse, l’inactivation du gène PaKmt6 conduit à un ensemble de défauts sévères : croissance végétative altérée, surproduction des gamètes mâles, malformations critiques des fructifications, production très réduite d’ascospores dont la germination est pour partie déficiente. Une étude d’épistasie a montré que les protéines PaRid et PaKmt6 interviennent chacune dans deux voies développementales distinctes. Par ailleurs, nous avons établi par immuno-précipitation de la chromatine les profils de distribution à l’échelle du génome entier des modifications H3K9me3, H3K27me3 et H3K4me3. Caractéristique rare, la marque H3K9me3 colocalise avec H3K27me3 sur des gènes transcriptionnellement réprimés et les séquences répétées ripées. Conformément à sa fonction canonique, H3K4me3 est présente en 5’ des gènes transcrits et est exclue des domaines H3K9me3 et H3K27me3. Comme attendue, PaKmt6 est essentielle à la mise en place de la marque H3K27me3, mais, de manière surprenante, elle serait aussi impliquée dans le dépôt et/ou le maintien d’une partie des marques H3K9me3, dévoilant ainsi une voie de méthylation non canonique de ces résidusIn pezizomycotina, transposable elements are targeted by a genome defense system named Repeat Induced Point Mutation (RIP). First described in Neurospora crassa, RIP occurs before karyogamy in each parental haploid nucleus of the dikaryotic cells and results, within the repeats, in de novo methylation of cytosine (5mC) and mutations, mainly C to T transitions. This initial step triggers local assembly of constitutive heterochromatin, which allows transcriptional gene silencing. RID (RIP Defective) is a putative cytosine methyltransferase essential for RIP. Despite the absence of 5mC in its genome, PaRid inactivation in Podospora anserina results in sexual reproduction arrest right after fertilization. In this context, we asked whether PaRid is required to silence expression of some of sexual development-specific genes by nucleation of constitutive heterochromatin. To this end, we identified PaKmt1 and PaHp1 genes encoding respectively the histone methyltransferase PaKmt1 (SU(VAR)39 homologue protein) and the heterochromatin protein 1 (PaHP1). To assemble constitutive heterochromatin, PaKmt1 catalyses tri-methylation of H3K9 (H3K9me3), latter on bound by PaHP1. By contrast, the E(Z) histone methyltransferase homologue PaKmt6, as part of the PRC2 complex, catalyses tri-methylation of H3K27 (H3K27me3) to form facultative heterochromatin. Our results showed that loss of either PaKmt1 or PaHP1 does not cause major defects. Conversely, PaKmt6 gene inactivation results in severe defects: altered mycelium and vegetative growth rate, overproduction of male gamete, development of crippled fructifications, reduced production ascospores, part of which does not germinate. Furthermore, epistatic study showed that PaRid and PaKmt6 likely act in two different developmental pathways, with respect to sexual reproduction. In addition, using chromatin immuno-precipitation we characterized H3K9me3, H3K27me3 and H3K4me3 genome-wide distribution patterns. We observed an uncommon overlapping distribution between H3K9me3 and H3K27me3 on transcriptionally repressed genes and RIP target repeats. As expected, H3K4me3 localizes in 5’ of the transcribed genes and is excluded from the H3K9me3 and H3K27me3 domains. As expected, PaKmt6 is essential for H3K27me3 modification, but surprisingly, could also be responsible for some of the H3K9me3 setting up or maintenance
24
Roohigohar, Shirin. « Characterisation of the interactions between Queensland fruit fly, Bactrocera tryoni, egg and larvae, and tomato fruit at the whole insect and molecular level ». Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/229382/1/Shirin_Roohigohar_Thesis.pdf.
Texte intégralRésumé :
Fruit flies are major pests to a wide range of fruits and vegetables as their larvae cause damage and yield loss. To replace pesticide-based controls with more sustainable management approaches, we need to develop new generation technologies. This thesis focuses on molecular and whole-organism studies to investigate the interactions between Queensland fruit fly larvae and tomato fruit. Through molecular analysis, different mechanisms were identified to determine the susceptibility of various tomato varieties to fruit fly damage. The results pave the way for future studies on breeding for fruit resistance to fruit fly attack and sustainable pest management.
25
Gianoli, Ernesto. « Induced responses of wheat to aphid feeding : consequences for both sides of the insect-plant interaction / ». Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1998. http://epsilon.slu.se/avh/1999/91-576-5455-7.pdf.
Texte intégral
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Trindade, Maria Margarida Silva. « Mecanismo de defesa e resistência das plantas a agentes patogénicos ». Master's thesis, Universidade de Évora, 2021. http://hdl.handle.net/10174/29296.
Texte intégralRésumé :
As plantas são constantemente ameaçadas por diversos microrganismos
patogénicos que prejudicam o seu crescimento e reprodução. Com isto, desenvolveram
eficientes mecanismos de defesa físicos e químicos que podem ser inatos ou induzidos.
Dependendo do tipo de interação com o patogénio, as plantas empregam estratégias
de defesa distintas e específicas para a patogénese, através de um sistema imunológico
multicamada, caracterizado por duas linhas de defesa: uma primeira, extracelular, que
pode desencadear respostas de largo espetro (PTI) e uma segunda, intracelular, em que
ocorre o reconhecimento muito específico do agente patogénico (ETI). Adicionalmente,
embora não tenham um sistema imunológico, podem criar resistência induzida, que se
caracteriza pela sinalização sistémica da resposta de defesa do local de infeção para as
partes distantes do mesmo, estabelecendo uma capacidade defensiva melhorada.
Compreender os mecanismos de defesa das plantas é fundamental para que se
possam obter plantas mais tolerantes ou mimetizar e induzir estes mecanismos; ABSTRACT: Plants defence and resistance mechanisms against pathogens
Plants are constantly threatened by several pathogenic microorganisms that harm
their growth and reproduction. With this, they developed efficient mechanisms of
physical and chemical defence that can be innate or induced. Depending on the type of
interaction with the pathogen, plants employ distinct and specific defence strategies for
the pathogenesis, through a multi-layered immune system, which is characterized by
two lines of defence: a first, extracellular, which can trigger wide-spectrum responses
(PTI) and a second one, with intracellular origin, in which the very specific recognition of
the pathogenic agent occurs (ETI). Additionally, although lacking an immune system,
they can create induced resistance, which is characterized by the systemic signalling of
the defence response from the infection site to the distant parts of it, establishing an
improved defensive capacity.
Understanding the defence mechanisms of plants is essential to obtain more
tolerant plants or to mimic and induce those mechanisms.
27
Nguyen, Trang Hieu. « Analysis of wound-induced jasmonate biosynthesis and signaling in defense and root development responses in rice ». Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTG034.
Texte intégralRésumé :
Le riz est la première céréale consommée dans l’alimentation avec plus de 600 millions de tonnes produites chaque année. Ainsi les contraintes d’ordre biotique et abiotique exercées sur cette céréale peuvent être particulièrement préjudiciables a la sécurité alimentaire. Des interactions moléculaires complexes orchestrant le développement des plantes et les mécanismes de défense face a des agents pathogènes ou a des contraintes climatiques jouent un rôle majeur dans l’adaptation des plantes. Récemment, il a été mis en évidence le rôle crucial joue par les hormones de défense tel que le jasmonate dans la modulation des réponses permettant aux plantes de s’adapter a leur environnement. Ainsi, le décryptage de la signalisation et des réponses au jasmonate présentent un intérêt majeur chez les céréales. Dans ce cadre, ces travaux de thèse ont permis d’analyser le rôle de cette phytohormone dans les réponses de défense locales et distales suite à un stress mécanique. De plus, par des approches fonctionnelles, un nouveau rôle du jasmonate a été mis en évidence dans le contrôle systémique du développement des racines coronaires sous stress chez le riz. La compréhension des mécanismes de réponse à la blessure et l’impact sur le développement, notamment au niveau de la partie « cachée » de la plante, le système racinaire, permet d'envisager la création de nouvelles variétés et l’optimisation de méthodes de culture du rizRice is the first cereal consumed by human with more than 600 million tons produced each year. Thus the biotic and abiotic constraints on this cereal can be particularly damaging to food security. Complex molecular interactions orchestrating plant development and defense mechanisms against pathogens or climatic constraints play a major role in plant adaptation. Recently, it has been highlighted the crucial role played by defense hormones such as jasmonate in modulating responses allowing plants to adapt to their environment. Thus, the analysis of signaling and responses to jasmonate are of major interest for cereals. In this context, this thesis work allowed to analyze the role of this phytohormone in local and distal defense responses following mechanical stress. In addition, by functional approaches, a new role of jasmonate has been demonstrated in the systemic control of stress-induced coronary root development in rice. The understanding of the mechanisms of response to injury and the impact on development, especially at the level of the "hidden" part of the plant, the root system, makes it possible to consider the creation of new varieties and the optimization of breeding methods and rice cultivation
28
Akturk, Ozgur. « Assessment Of Tunnel Induced Deformation Field Through 3-dimensional Numerical Models (necatibey Subway Station, Ankara, Turkey) ». Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612539/index.pdf.
Texte intégralRésumé :
In heavily settled areas, deformations induced by the tunnel excavation may cause
serious damage to nearby structures. In this study it is aimed to model ground
deformations induced by main tunnels and connection tunnels excavations as well
as groundwater drainage. Therefore, it is necessary to study effective means of
controlling tunnel induced deformations. The main parameters affecting the
failure and deformation state of the soil around a circular underground opening
are the physical characteristics of the soil, the diameter of the opening, and the
support pressure. During the construction stage of Necatibey Station of KizilayÇayyolu metro line (Ankara, Turkey), challenging ground conditions involving highly heterogeneous and locally water saturated foundation soils have been encountered. Possibility of damage at the surface and/or on the underground structures can be estimated using finite difference method (FDM) of analysis. In this study, two geophysical methods namely Electrical Resistivity Imaging (ERI) and Ground Penetrating Radar (GPR) were utilized to distinguish soil types at the study area. By correlating these geophysical survey results with the boring v logs, 3-Dimensional soil profile was revealed at the study area to build up a basis for numerical models. 3-Dimensional (3D) FDM analyses were conducted to assess tunneling induced deformations, along with movements around shallow soft ground main tunnels and connection tunnels. During sequential excavations, temporary and permanent shotcrete lining was also simulated. The soil behavior is assumed to be governed by an elastic-perfectly plastic constitutive relation based on the Mohr&ndash
Coulomb criterion. The computed deformations around these openings have been compared with the in-situ measurements. The results of the study revealed that the 3-D elasto-plastic analyses yield comparably good correlation with the in-situ measurements. Also, in this study, the effects of main tunnels excavations on each other and the effects of connection tunnels excavations on main tunnels were identified in terms of ground deformations. In order to simulate induced surface settlement due to groundwater withdrawal at the site 3-D fully coupled (fluidmechanical) numerical models were run using different time durations. The model studies revealed that deformations monitored at the ground surface are directly related with the tunnel construction practice. Pumping groundwater has very little or no effect on the measured deformations.
29
Hanak, Tobias [Verfasser], et Stefan [Akademischer Betreuer] Hoth. « Applicability of CRISPR/Cas9-mediated gene disruption in Brachypodium distachyon (L) P. Beauv to characterise the stress-induced 1,3-β-glucan synthase BdGSL3 in plant defence / Tobias Hanak ; Betreuer : Stefan Hoth ». Hamburg : Staats- und Universitätsbibliothek Hamburg, 2020. http://d-nb.info/1205880984/34.
Texte intégral
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Bairán, García Jesús Miguel. « A non-linear coupled model for the analysis of reinforced concrete sections under bending, shear, torsion and axial forces ». Doctoral thesis, Universitat Politècnica de Catalunya, 2005. http://hdl.handle.net/10803/6177.
Texte intégralRésumé :
La mayoría de las estructuras de hormigón armado se someten a solicitaciones combinadas de esfuerzos axiles, flexión, cortante y torsión. La fisuración del hormigón, plastificación de las armaduras y otros efectos no-lineales hacen que las secciones transversales de estos elementos presenten un comportamiento anisótropo que deriva en el acoplamiento de los esfuerzos normales y tangenciales. Es decir, esfuerzos normales o momentos flectores pueden producir deformaciones de corte y vice versa. Aunque en algunas ocaciones, esta interacción es considerada de forma simplificada en el dimensionamiento de estructuras, hasta el momento no se ha realizado un análisis profundo de los efectos acoplados en secciones de forma arbitraria bajo cargas 3D generales utilizando modelos de fibras.El objetivo principal de esta tesis es generalizar el análisis de secciones de hormigón armado mediante fibras, de forma que se pueda reproducir la res-puesta no-lineal acoplada frente a esfuerzos normales y tangenciales bajo solicitaciones tridimensionales generales. De igual forma, se pretende obtener, para los esfuerzos cortantes y torsión, la misma capacidad de representación de geometrías y combinación de materiales que ofrecen los modelos de fibras para esfuerzos de flexo-compresión.
La primera problemática estriba en representar adecuadamente la cinemática de la sección transversal. Con la excepción de las deformaciones normales contenidas en el plano de la sección, no existe una teoría cinemática que a priori pueda dar la distribución del resto de deformaciones o tensiones en la sección, sin dejar de satisfacer las condiciones de equilibrio interno o continuidad entre las fibras que componen la misma.
Por otra parte, para materiales anisótropos, como el hormigón fisurado, en general todos los esfuerzos internos pueden estar acoplados. Además, es preciso considerar la distorsión de la sección transversal para satisfacer el equilibrio entre fibras.
El problema se aborda de forma general, considerando una sección de forma y materiales cualesquiera. Se parte del problema diferencial de equilibrio de un sólido con el que se ha podido deducir un sistema de equilibrio entre fibras (equilibrio a nivel sección). Se puede demostrar que éste es complementario al problema estándar de vigas. El sistema complementario permite recuperar información tridimensional que normalmente se pierde al resolver un problema de vigas.
Posteriormente, se propone una solución interna del problema complementario, en la que el alabeo y la distorsión de la sección quedan expresados como una función de las deformaciones generalizadas de una viga: deformaciones axil y cortantes, curvaturas de flexión y torsión. No son necesarios grados de libertad adicionales a nivel estructura ni hipótesis a-priori sobre la forma de los campos de deformación o tensión interna.
A partir de la formulación teórica, se desarrolla un modelo de elementos finitos plano de la sección transversal. El modelo está preparado para servir como respuesta constitutiva de cualquier tipo de elemento viga en sus puntos de integración. %Se evita así la necesidad de realizar un modelo de elementos sólidos de toda la barra para estudiar la respuesta frente a una combinación general de esfuerzos normales y tangenciales.
Se implementan una serie de modelos constitutivos para distintos materiales. En particular, se implementa un modelo constitutivo triaxial para hormigón fisurado, considerando la anisotropía inducida por la fisuración e incluyendo la superficie de rotura según un criterio multiaxial.
La formulación seccional es validada mediante varios casos de estudio teóricos y experimentales. La respuesta no-lineal acoplada bajo diversas combinaciones de esfuerzos normales y tangenciales es reproducida con precisión, lo cual queda patente tanto en las curvas esfuerzo-deformación obtenidas como en las matrices de rigidez seccionales.
Finalmente, se recopilan las conclusiones derivadas de la presente investigación y se
ofren recomendaciones para futuros trabajos.
Most RC structures are subjected to combined normal and tangential forces, such as bending, axial load, shear and torsion. Concrete cracking, steel yielding and other material nonlinearities produce an anisotropic sectional response that results in a coupling between the effects of normal and shear forces, i.e. normal force or bending moments may produce shear strains and vice versa. Although this interaction is sometimes taken into account, in a simplified manner, in the design of RC structures, a deep analysis of the coupling effects of RC sections using fiber models has not yet been made for arbitrary shape sections under general 3D loading.
The main objective of this thesis is to generalize the fiber-like sectional analysis of reinforced concrete elements, to make it capable of considering the coupled non-linear response under tangential and normal internal forces, from a general 3D loading.
Similarly, it is desired to obtain, for torque and shear forces, the same capacity and versatility in reproducing complex geometry and materials combination that fiber-like sectional representations offers for bending and stretching.
The first problematic lies in finding a proper representation of the section's kinematics under such general loading. Except for in-plane normal strains, there is no single kinematical theory capable of a-priori representing the correct distribution of the others strains or stresses satisfying, at the same time, inter-fiber equilibrium and continuity. On the other hand, for rather anisotropic materials, such as cracked concrete, all internal forces are, in general, coupled. It is also required that distortion is allowed for the section's kinematics in order to guarantee satisfaction of internal equilibrium.
The problem is dealt in a general form considering arbitrary shaped sections and any material behaviour. Starting from the differential equilibrium of a solid, an inter-fiber equilibrium system (equilibrium at the sectional level) was deduced. This system, which is complementary to the standard equilibrium problem of a beam-column, allows to recuperate information of the three-dimensional problem that is generally lost when solving a beam problem.
Further, a solution of the equilibrium at the sectional level is proposed in which the section's warping and distortion are posed as a function of the generalized beam-column strains (axial and shear strains, bending and torsion curvatures). No additional degrees of freedom are required at the structural level nor a-priori hypotheses on the distribution of the internal strains or stresses.
After the theoretical formulation, a planar finite element model for cross-sectional analysis is developed. The model can be used as a constitutive law for general beam column elements at their integration points.
A series of constitutive models have been implemented for several materials. In particular, a triaxial constitutive model for cracked concrete is implemented considering crackinduced anisotropy and a multiaxial failure criterion.
The sectional formulation is validated by means of various theoretical and experimental case studies. Non-linear coupled response under normal and tangential internal forces is reproduced with accuracy, as can be seen both in the predicted internal force-strain curves and in the sectional stiffness matrixes.
Finally, the conclusions drawn from the current research are summarized and
recomendations for future works are given.
31
Muzammil, Saima. « Saccharothrix algeriensis NRRL B-24137 : biocontrol properties, colonization and induced systemic resistance towards Botrytis cinerea on grapevine and Arabidopsis thaliana ». Thesis, Toulouse, INPT, 2012. http://www.theses.fr/2012INPT0063/document.
Texte intégralRésumé :
Au cours de cette thèse, un isolat de sol de désert, Saccharothrix algeriensis NRRL B-24137, a été évalué pour ses propriétés bioactives contre le champignon phytopathogène Botrytis cinerea, pour sa colonization sur Vitis vinifera L., et Arabidopsis thaliana ainsi qu’en vue d’étudier les méchanismes de résistance systémique induite (ISR) contre B. cinerea. Les résultats obtenus nous ont permis premièrement de montrer que Sa. algeriensis NRRL B-24137 peut présenter des activités antifongiques contre B. cinerea et que des métabolites peuvent être responsables de cette activité antifongique. Bien que ces métabolites soient encore en cours d’étude et que cette étude mérite d’être approfondie, nous avons démontré ensuite les propriétés de colonisation de l’isolat du sol du désert chez la vigne. Les résultats ont permis de montrer que la souche peut former des populations rhizosphèriques ainsi que des sous-populations endophytiques chez des plants de vigne (Cabernet Sauvignon sur porte-greffe 44-53 M) à des étapes précoces de colonisation. Puis nous avons démontré que la souche bénéfique peut induire une résistance systémique contre B. cinerea. Bien que les mécanismes impliqués ne soient pas encore compris, des parties préliminaires de ces travaux démontrent que les expressions de gènes responsables de la production de glucanase, chitinase ainsi qu’un inhibiteur de polygalacturonase ne semblent pas potentialisés pendant le phénomène de résistance systémique. Enfin nous avons démontré l’interaction entre Sa. algeriensis NRRL B-24137 et Arabidopsis thaliana qui résulte dans une association intime dûe également à colonisation rhizosphèrique et endophytique de la plante modèle. La souche bénéfique peut églement induire un phénomène de résistance systémique sur A. thaliana contre B. cinerea et les analyses de plantes mutées ont permis de determiner des parties des mécanismes impliqués dans l’ISR aini que des nouveaux mécanismes impliqués qui peuvent être induits par des microbes bénéfiquesIn this thesis, the desert soil isolate, Saccharothrix algeriensis NRRL B-24137, has been evaluated for its bioactive properties towards the phytopathogenic fungus Botrytis cinerea, for its colonization of Vitis vinifera L., and Arabidopsis thaliana as well as to study the mechanisms of induced systemic resistance (ISR) towards B. cinerea. The results obtained allowed us firstly to show that Sa. algeriensis NRRL B-24137 can exhibit strong antifungal properties towards B. cinerea and that some metabolites can be responsible of this antifungal activity. Although these metabolites are still under consideration and that this study needs further works, we have demonstrated then the colonization properties of the desert soil isolate with grapevine plants. The results showed that the strain can form rhizospheric as well as endophytic subpopulations with grapevine plants (Cabernet Sauvignon cultivar graffed on 44-53 M rootstock) at early step of colonization. Then we have demonstrated that the beneficial strain could induce a systemic resistance towards B. cinerea. Although the mechanisms are not yet well understood, preliminary parts of this work demonstrated that the genes responsible of glucanase production, chitinase as well as inhibitor of polygalacturonase activity do not seems to be primed during the systemic resistance phenomenon. Finally we demonstrated that the interaction between Sa. algeriensis NRRL B-24137 and Arabidopsis thaliana plants results in a close association due also to a rhizo- and endophytic colonization of the model plant. The beneficial strain can also induce a systemic resistance in A. thaliana towards B. cinerea and analyzes of plant mutants have allowed to determine parts of the mechanisms involved in ISR as well as new mechanisms that could be trigerred by beneficial microbes
32
Merckel, Yannick. « Experimental characterization and modeling of the mechanical behavior of filled rubbers under cyclic loading conditions ». Phd thesis, Ecole Centrale de Lille, 2012. http://tel.archives-ouvertes.fr/tel-00736624.
Texte intégralRésumé :
Rubber-like materials are submitted to cyclic loading conditions in various applications. Fillers are always incorporated within rubber compounds. They improve the mechanical properties but induce a significant stress-softening under cyclic loadings. The physical source of the softening is not yet established and its modeling remains a challenge. For a better understanding of the softening, filled rubbers are submitted to cyclic loadings. In order to quantify the effects of the loading intensity and the number of cycles, original methods are proposed to characterize the softening. To study the influence of the material microstructure on the softening, compounds with various compositions are considered.Non proportional tensile tests including uniaxial and biaxial loading paths are applied in order to highlight the softening induced anisotropy. Such unconventional experimental data are used to provide a general criterion for the softening activation. A constitutive modeling grounded on a thorough analysis of experimental data is proposed. The model is based on a directional approach. The Mullins softening is accounted for by the strain amplification concept and is activated by a directional criterion. The model ability to predict non proportional softened material responses is demonstrated
33
Benelfellah, Abdelkibir. « Contribution à la modélisation de l'anisotropie induite par endommagement d'un matériau agrégataire énergétique ». Thesis, Tours, 2013. http://www.theses.fr/2013TOUR4018/document.
Texte intégralRésumé :
Le matériau composite agrégataire énergétique étudié a un comportement viscoélastique endommageable sensible à la pression de confinement et à la température. Ces travaux concernent la modélisation de l'anisotropie induite par endommagement avec deux objectifs principaux. Dans un premier temps, le caractère anisotrope de l'endommagement est mis en évidence expérimentalement. Des essais alternant tension et compression permettant d'observer l'effet unilatéral d'endommagement. Ensuite, un modèle de comportement est développé pour le matériau d'étude. Des modèles pertinents sont tout d'abord comparés. Le modèle le plus approprié est ensuite amélioré par l'ajout de mécanismes d'endommagement, d'effectivité du dommage et d'un mécanisme de plasticité. Les données expérimentales sont utilisées pour identifier les paramètres du modèle. Ce dernier a été ensuite implémenté dans un logiciel de calcul aux éléments finis (Abaqus / standard) sous la forme d'une procédure Fortran (UMAT). Différents types de chargements sont simulés et confrontés aux résultats expérimentauxAn explosive aggregate material exhibits a visco-elastic behaviour with damage, internal friction and sensitivity to the confining pressure and temperature. This thesis focuses on the anisotropic elastic damage with unilateral effect. The first aim of this study is to highlight experimentally the anisotropic nature of the damage. Then, a new model is proposed for the studied material. This is achieved using a comparison of some relevant models in order to select the most appropriate among them. The selected model is then improved by adding unilateral effect mechanisms and plasticity. Experimental data is used to characterize the material behaviour and to determine the parameters of improved model. This model has been implemented in the finite element software (Abaqus / Standard) using Fortran procedure (UMAT) and then tested for different loads and compared with experimental results
34
Ritter, Robert. « Verformungsverhalten und Grenzflächen von Ultrahochleistungsbeton unter mehraxialer Beanspruchung ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-132747.
Texte intégralRésumé :
Treten im Beton mehraxiale Spannungszustände auf, führen diese gegenüber einer einaxialen Beanspruchung zu einer signifikanten Änderung des Materialverhaltens. Neben einer festigkeitssteigernden bzw. -abmindernden Wirkung ergeben sich ebenfalls große Unterschiede im Spannungs-Dehnungs-Verhalten. Zur effizienten Konzipierung von Betonstrukturen unter komplexen Beanspruchungszuständen ist daher die Kenntnis des veränderten Materialverhaltens notwendig. Zur experimentellen Bestimmung des Spannungs-Dehnungs-Verhaltens eines Ultrahochleistungsbetons mit einer einaxialen Druckfestigkeit von über 170 N/mm² wurden mehraxiale Belastungsversuche an würfelförmigen Probekörpern durchgeführt. Die Untersuchung umfasste insgesamt 35 zwei- und dreiaxiale Spannungsverhältnisse unter proportionaler Laststeigerung mit vorrangiger Betrachtung von Zug-Druck-Druck-Beanspruchungen. Für die Einleitung der Zugbeanspruchungen in die Prüfkörper wurde eine neue Methode entwickelt, bei der mittels einbetonierter Schrauben die Belastung auf den Beton übertragen wird. Die Bestimmung des Verformungsverhaltens erfolgte im Inneren der Probekörper mit sechs tetraederförmig angeordneten Faser-Bragg-Gittern. Die somit direkt gemessenen Dehnungen ermöglichen die nachträgliche Berechnung der Komponenten des Dehnungstensors des Bezugskoordinatensystems. Für den untersuchten Ultrahochleitsungsbeton fallen die auf die einaxiale Druckfestigkeit bezogenen mehraxialen Festigkeitswerte mit zunehmendem hydrostatischen Druckspannungsanteil der Beanspruchung geringer aus als bei Normalbetonen. Weiterhin weist das Verformungsverhalten eine größere Sprödigkeit gegenüber Normalbetonen auf, so dass auch unter dreiaxialen Druckspannungszuständen die Probekörper schlagartig versagen. Aus den gemessenen Spannungs-Dehnungs-Linien werden neben den maximalen Festigkeiten die Festigkeitswerte an der Elastizitätsgrenze, der Affinitätsgrenze sowie beim Volumenminimum der Probekörper bestimmt. Zur Approximation dieser charakteristischen Werte wurde eine Grenzflächenbeschreibung entwickelt und an den Versuchsergebnissen kalibriert. Des Weiteren erfolgte die Zusammenstellung einer Datenbank mit in der Literatur verfügbaren mehraxialen maximalen Festigkeitswerten von Betonen mit einaxialen Druckfestigkeiten von 10 N/mm² bis 180 N/mm² und die Kalibrierung des entwickelten Modells zur Grenzflächenbeschreibung in Abhängigkeit der einaxialen Druckfestigkeit. Die bei der Kalibrierung der Grenzfläche für einzelne Betonfestigkeitsklassen bestimmten Freiwerte hängen dabei stark von den vorliegenden Versuchsdaten und speziell vom Wertebereich der hydrostatischen Spannungsanteile der maximalen Beanspruchungen ab. Die Approximation des Spannungs-Dehnungs-Verhaltens der mehraxial beanspruchten Probekörper erfolgt mittels eines schädigungsbasierten Materialgesetzes. Hierbei wird für den anfänglich isotropen Beton zum einen eine lastinduzierte isotrope Schädigung und zum anderen eine lastinduzierte orthotrope Schädigung angenommen, die von den auftretenden Hauptdehnungen abhängig ist. Mit dem entwickelten Materialgesetz werden sehr gute Übereinstimmungen mit den gemessenen Spannungs-Dehnungs-Linien erreicht, so dass sich ebenfalls eine gute Vorhersage der maximalen Festigkeitswerte ergibtConcrete under multiaxial stress states shows significant changes of the material behaviour compared to uniaxial loading. Besides strength increasing and decreasing effects, also great differences in the stress-strain behaviour occur. In order to design concrete structures efficiently concerning complex stress states, the knowledge about the modified material behaviour is necessary. To determine experimentally the stress-strain behaviour of an ultra high performance concrete with a uniaxial compressive strength of about 170 N/mm², multiaxial loading tests on cubic-shaped specimens were carried out. Altogether, the investigation contained 35 biaxial and triaxial stress ratios under proportionally increasing load with primarily tension-compression-compression loadings. Applying the tensile load on the specimen, a new method was developed, which uses screws embedded in the concrete to transfer the loading. The deformations were measured by using six tetrahedron-shaped arranged Fibre Bragg Gratings inside the concrete specimen. Subsequently, with the directly measured strains the components of the strain tensor of the reference coordinate system could be determined. For the investigated ultra high performance concrete the increase of the multiaxial strength, referring to the uniaxial compressive strength, decreases compared to normal strength concrete with the increasing hydrostatic stress component of the load. Moreover, the deformation behaviour shows an increased brittleness compared to normal strength concrete, so that even under triaxial compressive stress states the specimens fail abruptly. Besides the ultimate strength, from the measured stress-strain curves the strength at the proportional limit, at the limit of affinity as well as at the minimum volume of the specimen is determined. To approximate these characteristic values, a description of a hypersurface is developed and calibrated with the test results. Furthermore, a database with multiaxial ultimate strength values of concretes with uniaxial compressive strengths between 10 N/mm² to 180 N/mm² available from literature was compiled and a calibration of the developed hypersurface model depending on the uniaxial compressive strength was carried out. Thereby, the obtained values of arbitrary parameters of individual concrete strength classes depend severely on the available test results, especially on the range of values of the hydrostatic stress component of the ultimate strength. The approximation of the stress-strain behaviour of the multiaxial loaded specimens is carried out by means of a damage-based material law. For this purpose, concerning the initially isotropic concrete, a load-induced isotropic and orthotropic damage depending on the principle strains is assumed. With the developed material law, very good accordance with the measured stress-strain curves could be achieved, so that also results in a good approximation of the ultimate concrete strength
35
Speck, Kerstin. « Beton unter mehraxialer Beanspruchung ». Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1216628091575-43714.
Texte intégralRésumé :
Diese Arbeit basiert auf der Untersuchung von hochfesten und ultrahochfesten Betonen mit und ohne Fasern unter zwei- und dreiaxialer Druckbeanspruchung. Die Auswirkung der unterschiedlichen Betonzusammensetzung ist für verschiedene Beanspruchungen nicht gleich ausgeprägt, dennoch konnten grundlegende Zusammenhänge herausgearbeitet werden. Anhand der Bruchbilder konnten die drei Versagensmechanismen Druck-, Spalt- und Schubbruch identifiziert werden, deren Charakteristik über die Kalibrierung an vier speziellen Versuchswerten direkt in das Bruchkriterium einfließen. Dieses stellt eine Erweiterung der Formulierung von OTTOSEN dar, so dass das spröde und z. T. anisotrope Verhalten von Hochleistungsbeton berücksichtigt wird. Die beobachteten Spannungs-Dehnungs-Verläufe korrelieren mit den Versagensformen. Deshalb wird ein Stoffgesetz getrennt für den Druck- und den Zugmeridian aufgestellt, dessen Parameter sich mit zunehmendem hydrostatischen Druck verändern. In die Anfangswerte fließen die Betonzusammensetzung und herstellungsbedingte Anisotropien ein. Die lastinduzierte Anisotropie infolge einer gerichteten Mikrorissbildung wird in dem vorgestellten Stoffgesetzt über richtungsabhängige Parameter ebenfalls berücksichtigt.
36
Speck, Kerstin. « Beton unter mehraxialer Beanspruchung : Ein Materialgesetz für Hochleistungsbetone unter Kurzzeitbelastung ». Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23705.
Texte intégralRésumé :
Diese Arbeit basiert auf der Untersuchung von hochfesten und ultrahochfesten Betonen mit und ohne Fasern unter zwei- und dreiaxialer Druckbeanspruchung. Die Auswirkung der unterschiedlichen Betonzusammensetzung ist für verschiedene Beanspruchungen nicht gleich ausgeprägt, dennoch konnten grundlegende Zusammenhänge herausgearbeitet werden. Anhand der Bruchbilder konnten die drei Versagensmechanismen Druck-, Spalt- und Schubbruch identifiziert werden, deren Charakteristik über die Kalibrierung an vier speziellen Versuchswerten direkt in das Bruchkriterium einfließen. Dieses stellt eine Erweiterung der Formulierung von OTTOSEN dar, so dass das spröde und z. T. anisotrope Verhalten von Hochleistungsbeton berücksichtigt wird. Die beobachteten Spannungs-Dehnungs-Verläufe korrelieren mit den Versagensformen. Deshalb wird ein Stoffgesetz getrennt für den Druck- und den Zugmeridian aufgestellt, dessen Parameter sich mit zunehmendem hydrostatischen Druck verändern. In die Anfangswerte fließen die Betonzusammensetzung und herstellungsbedingte Anisotropien ein. Die lastinduzierte Anisotropie infolge einer gerichteten Mikrorissbildung wird in dem vorgestellten Stoffgesetzt über richtungsabhängige Parameter ebenfalls berücksichtigt.
37
Gros, Alice. « Modélisation de la cristallisation sous tension du caoutchouc naturel ». Thesis, Ecole centrale de Nantes, 2016. http://www.theses.fr/2016ECDN0018.
Texte intégralRésumé :
Bien que la cristallisation sous tension du caoutchouc naturel ait fait l'objet de nombreuses investigations expérimentales au cours du dernier siècle, et notamment dans les quinze dernières années, les résultats obtenus ne permettent toujours pas d'aboutir à une compréhension fine des mécanismes physiques en jeu, limitant la modélisation à des approches phénoménologiques. La présente thèse vise à élaborer un modèle rendant qualitativement compte des phénomènes observés lors d'un essai de traction uniaxiale du caoutchouc naturel. Dans un premier temps, une chaîne représentative modélise le réseau amorphe dont l'inhomogénéité est exprimée au travers de la distribution des longueurs des chaînes polymères qu'on suppose déformées à force égale. Les conditions de cristallisation et de fusion sont ensuite définies par la thermodynamique de changement de phase classique à laquelle est ajouté le caractère enchevêtré du réseau ; les conditions obtenues éclaircissent notamment la relation entre la déformation et la température lors de la fusion des cristallites. Finalement, un modèle de chaîne semicristallisée associant l'inhomogénéité des chaînes amorphes et l'hétérogénéité due à la présence de la phase cristalline est proposé, puis inclus dans une loi de comportement de type full-network dont les équations sont adaptées en conséquence. Ce travail aboutit à un modèle thermo-mécanique complet permettant de décrire qualitativement la réponse du caoutchouc naturel, ainsi qu'à une description interprétative originale de la cristallisation sous tensionDespite the numerous experimental inverstigations performed over the past century and more intensively in the last fifteen years, strain-induced crystallization taking place in natural rubber still remains hardly understood in its precise mechanisms, leading models to remain phenomenological ones. The present study aims to develop a physicallymotivated model which qualitatively reproduces physical phenomena observed during an uniaxial tensile test. Firstly, the amorphous network is assumed to deform in an equal-force manner, resulting in a representative chain encompassing the inhomogeneity of matter through the chain-length distribution. Secondly, based on classical thermodynamics and on the entangled nature of the polymer network, both crystallization and fusion conditions are established. Moreover the derivation of the equilibrium point of a finite crystallite in a deformed network clarifies the tight relation between deformation and temperature during fusion. Finally, a semi-crystallized chain is defined, accounting for both the inhomogeneity of the amorphous phase and the heterogeneity due to the presence of a crystalline phase. This chain is included in a modified full-network model, initially dedicated to amorphous networks. This work leads to a complete thermo-mechanical constitutive equation which qualitatively reproduces the response of natural rubber in tension, but also to an original interpretative description of strain-induced crystallization
38
« Defence genes in Citrus sunki and Poncirus trifoliata : expression constitutive and induced by Phytophthora parasitica ». Tese, BIBLIOTECA CENTRAL DA UFLA, 2005. http://bibtede.ufla.br/tede//tde_busca/arquivo.php?codArquivo=408.
Texte intégral
39
MARTINI, VALENTINA. « The role of terpenes in chemical defences of forest plants ». Doctoral thesis, 2010. http://hdl.handle.net/2158/545766.
Texte intégral
40
Brescia, David A. « Seasonal variation in constitutive and induced defenses of spruce (Picea spp.) hosts of the white pine weevil Pissodes strobi peck ». Thesis, 2000. http://hdl.handle.net/2429/11023.
Texte intégralRésumé :
The white pine weevil, Pissodes strobi, is a major pest of regenerating
spruce in British Columbia, and the damage caused by weevil attack results in a
severe reduction in plantation productivity and wood quality. As a result, the
planting of Sitka spruce, except in a small portion of its range, is no longer
recommended in B.C. Control attempts have met with little success; however, it
is believed that host resistance will be an essential part of an effective Integrated
Pest Management plan for the weevil. My objective was to examine the induced
resin response and the constitutive resin canal system of Sitka spruce to identify
potential resistance mechanisms and to determine how those mechanisms were
affected by seasonal growth and development of the tree.
Histological examination of cross-sections of laterals taken at different
times during the season were used to compare the extent of components of the
constitutive resin canal system between resistant and susceptible families of
Sitka spruce. Similar methods were used to compare the capacity of resistant
and susceptible trees to produce a traumatic resin response. Weekly
measurements of leader apical bud phenology and radial growth were used to
determine if differences in leader growth and development existed between
resistant and susceptible trees which could affect resin canal density in the
leader. Artificial wounding of tree leaders at different times of the season and at
different densities of wounding was used to determine if there was a seasonal
effect on the production of traumatic resin and if the response level was related
to the wounding level.
Compared to susceptible trees, resistant trees tended to have larger inner
resin canals and thinner bark, and thus, a greater percentage of bark occupied
by inner resin canals. Furthermore, both resistant and susceptible trees showed
an increase in resin canal size and a decrease in resin canal density through the
season. The level of the traumatic response produced by artificially wounded
trees was significantly higher in resistant trees than in susceptible trees and was
also found to be highest in early flushing trees. No difference in rate of leader
radial growth was observed between resistant and susceptible trees, but buds
on resistant trees flushed earlier than those on susceptible trees. The traumatic
response was found to be lowest in trees wounded early in the season, and was
also found to increase in a density dependent manner with the wounding level.
Although several traits were present to a greater degree in resistant trees
than susceptible trees, no single trait was emphasized in every resistant
individual, suggesting that effective resistance is based on a combination of
traits. Furthermore, the variability of these traits through the season reinforces
the importance of host-insect phenology in the success or failure of an attack.
41
Reiter, Chad E. N. « Constitutive insulin receptor signaling in retina and changes induced by diabetes / ». 2004. http://www.etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-635/index.html.
Texte intégral
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Jou, Yeun-Wen, et 周允文. « Mechanical Behavior and a Constitutive Model for Shear Induced Anisotropic Softening of Gravelly Soil ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/15562892182967690133.
Texte intégralRésumé :
博士國立中興大學
土木工程學系所
98
To characterize the deformational behavior of gravelly soils, this paper focuses on the individual influence of hydrostatic pressure and pure shearing on deformational behavior. Firstly, a series of drained, triaxial compression tests was conducted upon large specimens those made of gravelly soils, in which grain size distribution curve was based on the field condition. Furthermore, to distinguish the volumetric and the shear deformation of the gravelly soils, experiments with controlled stress paths, firstly hydrostatic compressed and followed by pure sheared, were conducted, respectively. Accordingly, a simple, yet innovative, constitutive model is proposed. The proposed constitutive model is characterized by the following features of gravelly soils: (1) significant shear-induced volumetric deformation prior to failure, (2) modulus stiffening under hydrostatic loading and softening under shearing condition; and (3) stress-induced anisotropy. In the proposed model, the deformational moduli K and G would vary according to the stress state. The stiffening and softening of these moduli render the diverse deformational behavior of gravelly soils. In addition, an anisotropic factor β is introduced to reflect the stress-induced anisotropy. Moreover, the proposed model only needs eight material parameters, and all these parameters can be rather easily obtained from experiments.
43
Liao, Chun-Yi, et 廖俊逸. « A preliminary study on time dependent constitutive model for shear induced anisotropic softening of sandstone ». Thesis, 2008. http://ndltd.ncl.edu.tw/handle/53483682914317426353.
Texte intégralRésumé :
碩士國立臺灣大學
土木工程學研究所
96
Owing to the special geological background of Taiwan, weak rock in western Taiwan sedimentation strata has shear dilation and creep deformational behaviors. During the underground excavation, often have a large amount of compression deformation then result in disaster. General deformed characteristics for geo-materials are nonlinear. Using linear elastic model to compute the deformation of geo-materials will always misestimate. So it is necessary to develop a constitutive model that apply to geo-material. This research, based on the results of tri-axial test with the sandstone in western Taiwan that performed by Rock Mech. Lab. of NTU. To sum up the following deformation behavior of sandstone: (1) under shear loading will transform from its original isotropy to a shear-induced anisotropic (2) the shear dilation behavior will still exist under creep test According to the deformation behavior of sandstone, the concepts of shear modulus softening and anisotropic factor are used to develop an anisotropic softening model. And combine with the visco-elastic model to develop a time dependent model for anisotropic softening of sandstone. Then write subroutine of the model to apply it to numerical analysis. The model with three parameters bulk modulus K, shear modulus G and anisotropic factor β to simulate instant deformation and another three parameters Kc, Gc and viscosity η to simulate creep deformation. With several sets of pure shear tests and creep test we can get all the parameters. Through the simulations of different confined pressure and different stress path tests, it is found that good agreements with instant deformation of sandstone, but the creep deformation in high shear stress state are have some different. However the trend of simulations are consistent with the experimental results. Apply the model to finite element method of ABAQUS program. Writing user subroutine to define the material''s mechanical behavior. Before analyzing the tunnel cases, single element test was applied to verify the accuracy of the subroutine. Then apply the model to tunnel excavation analysis. Comparing prediction results between the anisotropic softening model, elastic model and Drucker-Prager model. The numerical results show that, with the proposed model there is a uniform compression zone around tunnel section and the inward displacements (including the crown, sidewalls and invert) based on anisotropic softening model are larger then elastic model and Drucker-Prager model. Keywords: sandstone, constitutive model, softening, shear dilation, creep.
44
Zeng, Jia [Verfasser]. « Interferon induced and constitutive expression of immunity related GTPases (IRG) in mouse tissues / vorgelegt von Jia Zeng ». 2008. http://d-nb.info/988222183/34.
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Gagnon, Hubert. « The isoflavonoids of Lupinus albus, their constitutive and environmentally induced accumulation and secretion, and their effect on bacterial growth ». Thesis, 1993. http://spectrum.library.concordia.ca/5187/1/MM90835.pdf.
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Mutyambai, Daniel Munyao. « Exploiting early herbivory-induced defense traits in Zea species for the management of Chilo partellus in East Africa / Daniel Munyao Mutyambai ». Thesis, 2014. http://hdl.handle.net/10394/15461.
Texte intégralRésumé :
Maize, a genetically diverse crop, is the third largest cereal crop in the world and the
most important staple cereal in sub-Saharan Africa, supplying 50% of the calorie intake
in this region. The stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) is a
key constraint to cereal production in most resource-poor smallholder farming systems
in sub-Saharan Africa causing crop losses accruing up to 88%. Previous studies have
shown that feeding by herbivorous insects induces maize to emit volatiles attractive to
natural enemies. However, these antagonists are recruited when damage has already
been inflicted on the plant. Recent investigations revealed that egg deposition can
induce maize landraces of Mesoamerican origin to emit volatiles attractive to C.
partellus parasitoids, a trait previously reported to be absent in maize hybrids. However,
genotypic variation in this indirect defence trait within maize varieties adapted to local
agroclimatic conditions and the effect of processes such as domestication and breeding
on this trait are not known. Moreover, it is not known whether maize varieties
possessing this indirect defence trait can directly deter further herbivore colonization
and constitutively suppress the herbivore‟s larval development or whether they can
induce the same defence trait in neighbouring unattacked plants. This study sought to
fill these knowledge gaps with the aim of exploiting these plant defence traits in the
development of ecologically sound crop protection strategies. Experiments were
conducted in which headspace volatile samples were collected from plants of wild,
landrace and hybrid maize with and without C. partellus eggs. Chemical analyses were
done using gas chromatography (GC), coupled GC-mass spectrometry (GC-MS) and
coupled GC-Electroantenography (GC-EAG). Behavioural bioassays were done using
egg (Trichogramma bournieri Pintureau (Hymenoptera: Trichogrammatidae)) and larval
(Cotesia sesamiae Cameron (Hymenoptera: Braconidae)) parasitoids in a 4-arm
olfactometer using volatiles collected from the plants. Moreover, C. partellus larval
preference, growth and development as well as subsequent oviposition behaviour of
gravid C. partellus moths on these plants were determined. Behavioural assays showed
that both T. bournieri and C. sesamiae preferred volatiles from four of the five wild
teosinte species, five landraces and one of two maize hybrids exposed to egg
deposition. Similarly, volatiles collected from unoviposited maize landrace plants
exposed to oviposited landrace maize plants emitting oviposition-induced volatiles, were
attractive to both egg and larval parasitoids. Moreover, maize varieties emitting these
oviposition-induced volatiles deterred further herbivore colonization and suppressed
larval development. Volatile analysis by GC and GC-MS revealed marked increases in
volatile emission as well as qualitative changes in the odour blends in four wild types,
five landraces and one hybrid, following stemborer oviposition. Coupled GC-EAG
analysis of attractive samples revealed that C. sesamiae was responsive to (E)-2-
hexenal, (Z)-3-hexen-1-ol, nonane, 6-methyl-5-heptene-2-one, α-pinene, myrcene,
limonene, (E)-4,8-dimethyl-1,3,7-nonatriene, decanal, 3,4-dimethylacetophenone and
(E)-β-farnesene. Results from this study provide insights into tritrophic interactions thus
paving the way for designing novel and ecologically sound pest management strategies
through breeding crops with this novel oviposition-induced defence trait.PhD (Environmental Sciences), North-West University, Potchefstroom Campus, 2015
47
Won, Doyon. « Hemodynamic Regulation of Endothelial Cell Gene Expression : Effects of p65 Expression Level on Constitutive and TNFα Induced NF-κB Signalling ». Thesis, 2009. http://hdl.handle.net/1807/17842.
Texte intégralRésumé :
Atherosclerosis is a chronic inflammatory disease of arterial blood vessels, characterized by deposition of lipoproteins in the arterial wall. Atherosclerotic plaques form preferentially in distinct regions of the vasculature such as branch points, curvatures and bifurcations, suggesting that local hemodynamic forces may contribute to disease susceptibility. Shear stress imparted on endothelial cells (ECs) by the flowing blood has been shown to modulate gene expression and remodelling of the artery.
In this thesis, an in vitro model was established to recreate the contrasting environments found in atherosclerosis-prone and atherosclerosis-resistant regions of the vasculature to demonstrate a direct causal-relationship between shear stress and expression of endothelial nitric oxide synthase (eNOS) and p65 in ECs. In vitro assessment of cell shape and expression patterns of these anti- and atherogenic genes demonstrated that shear stress can induce cell morphology and gene expression patterns that are similar to ECs in atherosclerosis-prone and atherosclerosis-resistant regions of the mouse vasculature. Regulation of eNOS transcription by shear stress was demonstrated using a transgenic mouse model and in vitro heterogeneous nuclear RNA (hnRNA) quantification.
Similar to ECs in atherosclerosis-prone regions, epithelial cells lining the small intestine lumen express high levels of p65. To investigate the effects of p65 expression levels on constitutive and tumour necrosis factor α (TNFα)-induced nuclear factor-κB (NF-κB) signalling, p65 expression was suppressed in HeLa cells by RNA interference. Lower p65 expression resulted in reduced TNFα-induced expression of NF-κB target genes, including many subunits of inhibitor of nuclear factor κB (IκB), demonstrating modulation of NF-κB priming by p65 expression levels. Suppression of p65 also affected constitutive expression levels of IκB, and resulted in re-setting of the NF-κB/IκB equilibrium. Experiments using inhibitors of canonical NF-κB signalling found that basal expression of NF-κB components is independent of nuclear factor κB kinase β (IKKβ) activity and proteasome-mediated degradation of IκBα. Together, these studies elucidate the mechanism of flow-mediated gene regulation and the effect of resulting changes in p65 expression on NF-κB signalling.
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Rampersaud, Andy. « Chromatin accessibility and epigenetic changes induced by xenobiotic and hormone exposure in young adult mouse liver ». Thesis, 2019. https://hdl.handle.net/2144/39470.
Texte intégralRésumé :
Transcription factors activated by exogenous or endogenous stimuli alter gene expression with major effects on chromatin accessibility and the epigenome. This thesis investigates that impact of environmental chemical and hormonal exposure on liver chromatin accessibility in a mouse liver model. Exposure to the constitutive androstane receptor (CAR)-specific agonist ligand 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) induces localized changes in chromatin accessibility at several thousand DNase hypersensitive sites (DHS). Activating histone marks, associated with enhancers and promoters, were induced by TCPOBOP and were highly enriched at opening DHS. Opening DHS were highly enriched for CAR binding sites and nuclear receptor direct repeat-4 motifs. These DHS were also enriched for the CAR heterodimeric partner RXRA, binding by CEBPA and CEBPB, and motifs for other liver-specific factors. Thus, TCPOBOP alters the enhancer landscape through changes in histone marks and by mechanisms linked to induced CAR binding. In other studies, the impact of pituitary growth hormone (GH) secretion patterns on chromatin accessibility changes associated with sex-biased liver gene expression was examined. In adult male liver, the transcription factor STAT5 is directly activated by each successive plasma GH pulse. In female liver, STAT5 is persistently activated by the near-continuous stimulation by plasma GH. A majority of the ~4,000 GH-regulated, sex-biased DHS have chromatin marks characteristic of enhancers and were enriched for proximity to sex-biased gene promoters. Chromatin accessibility is thus a key feature of sex-differential gene expression. Two major classes of male-biased DHS were identified: dynamic male-biased DHS, almost all bound by STAT5, which undergo repeated cycles of chromatin opening and closing induced by each GH pulse; and static male-biased DHS, whose accessibility is unaffected GH/STAT5 pulses and whose sex bias results from these chromatin sites being more closed in female liver. Sites with STAT5 binding showed greater chromatin opening, many of which also contain the STAT5 motif. Finally, the effect of a single GH pulse on hypophysectomized male mouse liver was investigated to identify DHS responsive to the male, pulsatile-GH, secretion pattern. These studies demonstrate that widespread epigenetic changes associated with target gene expression are induced by xenobiotics and hormones regulating liver gene expression.2022-01-31T00:00:00Z
49
Colgan, Lindsay Jessica. « Induced monoterpene responses in jack pine : defence against jack pine budworm and a fungal associate of the mountain pine beetle ». Master's thesis, 2010. http://hdl.handle.net/10048/1307.
Texte intégralRésumé :
My thesis research investigated monoterpene responses in jack pine (Pinus banksiana Lamb.) to different agents to better understand how these responses may influence the spread of the mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB) in the boreal forest. The results support that monoterpenes are inducible responses in jack pine. In the first study, methyl jasmonate application elicited the greatest response in juvenile and mature trees suggesting that jasmonic acid plays a role in jack pine defence responses. In the cross-induction study, I found evidence of an increase in resistance to Grosmannia clavigera with prior jack pine budworm defoliation (Choristoneura pinus pinus Freeman; JPBW). In contrast, needle monoterpenes greatly increased after G. clavigera inoculation and continued to increase during JPBW defoliation; however, JPBW increased its feeding rate to compensate for a change in host quality. Overall, monoterpene induction in jack pine depended on the agent(s) involved and their order. The systemic responses that were observed may have implications for MPB spread in the boreal forest.Forest Biology and Managment
50
Choi, Ka-Yee Grace. « Molecular mechanisms and effector functions of the human cathelicidin host defence peptide LL-37 : modulation of cytokine IL-32γ-induced responses and inflammatory arthritis ». 2017. http://hdl.handle.net/1993/32183.
Texte intégralRésumé :
Current therapies for chronic inflammatory diseases often abrogate the immune functions required to fight infections. Human cathelicidin host defence peptide (HDP) LL-37 selectively suppresses pathogen-induced inflammation, without compromising resistance to infections. These unique dual abilities of LL-37 make it a promising candidate as an alternative therapeutic for treating chronic inflammatory diseases. The objective of this study was to investigate the effects of LL-37 and its derivative peptide IG-19 in cytokine-mediated inflammation. I demonstrated that LL-37 and IG-19 selectively suppressed cytokine IL-32γ-induced pro-inflammatory cytokines, without compromising the production of anti-inflammatory cytokines, and chemokines in human PBMC and macrophages. However, significant quantitative differences between LL-37 and IG-19-mediated chemokine productions suggested that the mechanisms underlying the activity of these two peptides were different.
I showed that both peptides suppressed IL-32γ-mediated phosphorylation of the Src-kinase FYN(Y420), known to enhance inflammation. Contrastingly, phosphorylation of the dual phosphatase MKP-1(S359), a negative regulator of inflammation, was enhanced in response to both peptides. Similarly, both peptides increased the activity of p44/42MAPK, which phosphorylates and stabilizes MKP-1. These results suggested that MKP-1 may be a critical mediator of the immunomodulatory activity of these peptides.
Bioinformatic interrogation revealed that direct interacting protein partners of MKP-1 were overrepresented in MAPK and NF-κB signalling pathways. Both peptides enhanced the phosphorylation of p38MAPK. However, contrasting to LL-37, IG-19 did not mediate the phosphorylation of JNK MAPK and IKK-α signaling intermediates involved in inflammation. This was consistent with observations that chemokine production was significantly lower in response to IG-19 compared to LL-37. These results suggested that IG-19 may be a better immunomodulatory therapeutic candidate compared to LL-37.
As cytokine-mediated inflammation plays critical roles in the disease pathogenesis of inflammatory arthritis, I examined the effects of exogenous administration of IG-19 in a murine model of collagen-induced arthritis. Administration of IG-19 decreased disease severity, suppressed pro-inflammatory cytokines and anti-collagen antibodies, and mitigated cartilage destruction in the CIA mice. These results provide a rationale to further develop IG-19 as a therapeutic agent for chronic inflammatory arthritis. The advantage of HDP based therapy is the potential to control inflammation without compromising the patient’s ability to resolve infections.May 2017