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Khan, Asif Ali. "Breeding maize for stress tolerance." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366240.
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Alexandre, Ana Isabel Pereira. "Temperature stress tolerance in chickpea rhizobia." Doctoral thesis, Universidade de Évora, 2010. http://hdl.handle.net/10174/11582.
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The aims of the present thesis were to study the chickpea rhizobia diversity and biogeography using Portugal as case study; to evaluate the temperature stress tolerance of the isolates, and to investigate the molecular basis of stress tolerance. The phylogenetic performance of the co-chaperone dnaJ was also addressed, in order to find an altemative marker to 16S rRNA gene. According to the 16S rRNA gene phylogeny, most isolates were found to be distinct from the typical chickpea rhizobia species, Mesorhizobium cíceri and M. mediterraneum. Some provinces of origin are associated with particular species groups. dnaJ was found to be a Useful phylogenetic marker for Mesorhizobium and for the Alphaproteobactería class. The evaluation of temperature stress tolerance revealed tolerant and sensitive isolates to both
heat and cold. Analysis of the expression of dnaK and groESL chaperone genes suggested that higher induction of these genes is related to higher tolerance to heat. ### - Resumo - A presente tese teve como objectivos o estudo da diversidade e biogeografia de rizóbio de grão-de-bico em Portugal, a avaliação da tolerância dos rizóbios ao stress térmico, bem
como o estudo das bases moleculares da tolerância ao stress. Estudou-se, ainda, o gene da co-chaperone dnaJ do ponto de vista filogenético.
A filogenia baseada no gene 16S rRNA revelou que a maior parte dos rizóbios de grão-de-bico agrupam com outras espécies, que não as típicas desta leguminosa (Mesorhizobium cicerí e M. mediterraneum). Encontrou-se uma associação entre algumas províncias e determinadas espécies de rizóbio. O gene dnaJ revelou-se um bom marcador filogenético para Mesorhizobium, bem como para a classe Alphaproteobactería. A avaliação da tolerância à temperatura permitiu diferenciar isolados tolerantes e sensíveis, a altas e baixas temperaturas. A análise da expressão dos genes dnaK e groESL, sugeriu que uma maior indução destes genes está relacionada com maior tolerância a altas temperaturas.
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Paralkar, Urvi Pradeep. "RELATIONSHIP BETWEEN TOLERANCE OF AMBIGUITY, TOLERANCE OF UNCERTAINTY, AND COPING WITH ACADEMIC STRESS." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/theses/2522.
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Sheen, Tamsin, and n/a. "Osmotic and desiccation stress-tolerance of Serratia entomophila." University of Otago. Department of Microbiology & Immunology, 2008. http://adt.otago.ac.nz./public/adt-NZDU20081208.114925.
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Serratia entomophila, the causative agent of amber disease, is an endemic bacterium used for the biocontrol of New Zealand grass grub larvae. Although the available biopesticide is effective, its use is limited to areas where sub-surface application is feasible, and is also impacted by soil conditions such as moisture levels and osmolarity. The aim of this study was to elucidate the responses of S. entomophila to osmotic and desiccation stresses in relation to challenges encountered during production, storage and soil application, with the goal of developing a more robust and versatile biocontrol agent.
RpoS is a key factor in the stress response of many enteric bacteria. In order to dissociate the effect of RpoS from subsequent cellular stress studies, an rpoS mutant was constructed by site-directed mutagenesis. Assessment of the rpoS mutant showed that RpoS was not implicated in NaC1 or desiccation tolerance of S. entomophila. The rpoS mutant was instead found to have enhanced salt tolerance and could be distinguished from the wild-type by the ability to ferment arabinose, a phenotype that was confirmed through complementation. Complete abolition of the amber disease process was observed using an rpoS strain also missing the Sep virulence genes, suggesting that RpoS is a regulator of the S. entomophila anti-feeding prophage (Afp). These findings indicate a subtle interplay between NaC1 tolerance, virulence and RpoS-mediated regulation of amber disease in S. entomophila.
A transposon mutagenesis screen was carried out to identify genes associated with NaC1 tolerance in S. entomophila. Fourteen mutants displaying NaC1 sensitivity were identified, two of which had mutations in genes with potential implications for the formulation of the bacterium as a biocontrol agent. The gene leuO that encodes a LysR-family transcriptional regulator was found to be essential for S. entomophila NaC1 tolerance. The toxicity of increased cellular LeuO from an over-expression vector led to the investigation of the effects of leuO mutation on the proteome. Multiple protein changes observed by two-dimensional gel analysis suggested that LeuO may be a global regulator in S. entomophila, as has been hypothesised for Salmonella species. A second NaC1-sensitive mutant contained an insertion in afp15, the product of which is thought to be involved in assembly of the Afp. As well as being sensitive to NaC1, the afp15 mutant was unable to induce the anti-feeding component of amber disease, again highlighting the link between stress tolerance and virulence in S. entomophila.
This study also determined that pre-exposure to NaC1 in conjunction with the provision of exogenous glycine betaine significantly enhanced the survival of S. entomophila either in a desiccated state or after application to soil, regardless of the soil moisture content. The implication of this finding on the future formulation of S. entomophila led to investigation of the underlying genetic mechanisms involved in glycine betaine synthesis and NaC1 tolerance. The genes involved in glycine betaine biosynthesis from choline were identified through genomic comparison, degenerate PCR and primer walking. A 6.5 kb region was sequenced and found to contain four genes with homology and similar chromosomal arrangement to the E. coli bet genes (betTIBA). The S. entomophila betIBA genes comprised an operon, flanked by the divergently-transcribed betT gene whose product is responsible for choline transport. To ascertain the relative transcription levels of components of the bet operon, quantitative RT-PCR was performed. Results of qRT-PCR showed that choline in conjunction with NaC1 induced the greatest levels of bet gene transcription, and that levels of the betA transcript were significantly lower than those of the other bet genes. Examination of the betA 5� non-coding region identified a previously undetected hairpin region, possibly accounting for the observed decrease in betA transcript levels.
The findings of this study have significantly advanced our understanding of how S. entomophiia responds to stress, and will contribute to the development of formulation strategies for the production of a robust product capable of application to pasture by a range of teclmiques. In addition, there is significant potential to utilise these findings in the development of other bacterial inocula for a range of biotechnological applications.
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Akhtar, Lal Hussain. "Tissue culture and stress tolerance in Gossypium species." Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296184.
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Howden, Reuben. "Tolerance to orthostatic stress and human cardiovascular control." Thesis, De Montfort University, 2002. http://hdl.handle.net/2086/4812.
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Ahmed, Helal Uddin. "Mapping stress tolerance genetic loci in Arabidopsis thaliana." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246628.
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Neudeck, Michelle Joan. "Tolerance of Planktothrix agardhii to nitrogen depletion." Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1522329471601801.
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MACHADO, VERONICA MIQUELIN. "EFFECT OF ELASTIC-PLASTIC STRESS IN THE DEFECT TOLERANCE UNDER STRESS CORROSION CRACKING." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33679@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Corrosão sob tensão (SCC), que consiste na iniciação e propagação de trincas devido ao efeito combinado de tensões mecânicas e o ambiente corrosivo, é um dano potencial para estruturas e componentes. Além do mais, SCC pode ser explicado por diferentes mecanismos dependendo do par material ambiente corrosivo considerado, o que dificulta o uso de um modelo geral para predizer o comportamento de trincas em SCC. Sendo assim, projetos frequentemente utilizam um critério conservativo que desqualifica materiais susceptíveis à SCC sem analisar de maneira apropriada a influência dos campos de tensão que a induzem. O objetivo deste trabalho é avaliar o efeito de tensões elastoplásticas na corrosão sob tensão. Esta abordagem mecânica considera que todos os efeitos corrosivos envolvidos na corrosão sob tensão podem ser apropriadamente quantificados pelas tradicionais resistências do material à iniciação e propagação de trincas para um ambiente corrosivo específico. Corpos de prova de flexão em Alumínio fragilizados por Gálio líquido serão utilizados para prever o efeito de tensões residuais induzidas por deformações plásticas na iniciação de trincas por corrosão sob tensão. Além disso, uma análise quantitativa baseada no comportamento de trincas não propagantes a partir de entalhes será usada para estimar a tensão necessária para iniciar e propagar trincas em corpos de prova entalhados em aço AISI 4140 sujeitos à corrosão por sulfeto de hidrogênio em ambiente aquoso. O comportamento de trincas curtas e a carga máxima suportada pelos corpos de prova entalhados são analisadas considerando campos de tensões lineares elástico e elastoplásticos através do modelo proposto que será validado através de dados experimentais.
Stress Corrosion Cracking (SCC), which consist in the initiation and propagation of cracks due to the combined attack of mechanical stresses and a corrosive environment is a potential danger for structures and components. Moreover, SCC can be explained by different mechanisms depending on the metal environmental pair, what makes difficult to create a generalized analytical approach to predict the crack behavior in SCC. Therefore, projects often use an over-conservative design criteria that disqualify a material susceptible to SCC without properly evaluate the influence of the stress fields that drive them. The aim of this work is to evaluate the effect of elastic-plastic stress in SCC. This mechanical approach assumes that all chemical effects involved in SCC problems can be appositely described and quantified by traditional material resistances to crack initiation and propagation at under specific environment. Aluminum bending specimens in Gallium environment are used to predict the effect of the residual stress induced by plastic deformation in the crack initiation under SCC conditions. Furthermore, a quantitative analysis based on the non-propagating crack behavior departing from notch tips are used to calculate the necessary stress to initiate and propagate SCC in AISI 4140 steel notched specimens under aqueous hydrogen sulfide environment. The non-propagating crack behavior and the maximum load supported by notched specimens are analyzed under linear elastic and elastic-plastic stress field through the proposed model that will be validated by experimental data.
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Green, Andrew Justin. "Abiotic stress tolerance from the tertiary gene pool of common wheat." Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32746.
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Doctor of PhilosophyDepartment of Agronomy
Allan K. Fritz
Heat and drought stress are two of the most significant abiotic stresses limiting wheat production in the Great Plains and worldwide. Introgression of novel tolerance genes from wild relatives is a strategy which presents promise. This study examined both heat and drought tolerance from the tetraploid species Aegilops geniculata (U[superscript g]U[superscript g]M[superscript g]M[superscript g]). Additional screening for heat tolerance was conducted with the US genome species Aegilops peregrina (Hack) and Aegilops kotschyi (Boiss). A comprehensive screening system for drought tolerance was also constructed to evaluate wheat and its wild relatives. Previous reports suggested that Ae. geniculata accession TA2899 was moderately tolerant to heat stress. It had also previously been used to develop a full set of wheat-Ae. geniculata chromosome addition lines in a Chinese Spring background. To identify the chromosome(s) carrying the heat tolerance, all addition lines, as well as wheat check genotypes, were screened for post-anthesis heat tolerance in two growth chamber experiments. No chromosome addition lines were significantly different (p<0.05) from Chinese Spring, and none were found to have superior performance to the positive check cultivars. Forty-five accessions of Ae. peregrina and its close relative, Ae. kotschyi were screened in a post-anthesis heat experiment. A follow-up experiment compared the genotypes in a split-plot temperature treatment with heat and optimal growth chambers. Many accessions were similar to the control genotypes for grain fill duration, and some exceeded the wheat controls for relative chlorophyll index values on Day 12 and Day 16. TA1889 and TA1904, both Ae. peregrina accessions originating from Israel, had a higher grain fill duration across experiments than the best wheat control, and warrant further investigation. Previous reports suggested drought tolerance in Ae. geniculata. After preliminary screenings, six genotypes were selected for advanced screening and compared with three wheat cultivars. The advanced greenhouse screening system was conducted in 152cm tall PVC growth tubes. The experiment measured multiple plant responses, and had a datalogging system automatically collecting water content and matric potential of the growth media. Multiple accessions warranted further investigation, and showed potentially different modes of drought tolerance, with varying levels of stomatal resistance, biomass, and osmotic adjustment.
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Gass, Thomas Gass Thomas. "Tolerance of soybean to low temperature stress during flowering /." [S.l.] : [s.n.], 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10771.
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Helaly, Alaa el-Din A. "Molecular studies on plants to enhance their stress tolerance." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=974309494.
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Krell, Andreas. "Salt stress tolerance in the psychrophilic diatom Fragilariopsis cylindrus." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980889235.
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Helaly, Alaa El-din A. "Molecular studies on plants to enhance their stress tolerance." Phd thesis, Universität Potsdam, 2004. http://opus.kobv.de/ubp/volltexte/2005/242/.
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Environmental stresses such as drought, high salt and low temperature affect plant growth and decrease crop productivity extremely. It is important to improve stress tolerance of the crop plant to increase crop yield under stress conditions. The Arabidopsis thaliana salt tolerance 1 gene (AtSTO1) was originally identified by Lippuner et al., (1996). In this study around 27 members of STO-like proteins were identified in Arabidopsis thaliana, rice and other plant species. The STO proteins have two consensus motifs (CCADEAAL and FCV(L)EDRA). The STO family members can be regarded as a distinct class of C2C2 proteins considering their low sequence similarity to other GATA like proteins and poor conservation in the C-terminus. AtSTO1 was found to be induced by salt, cold and drought in leaves and roots of 4-week-old Arabidopsis thaliana wild-type plants. The expression of AtSTO1 under salt and cold stress was more pronounced in roots than in leaves. The data provided here revealed that the AtSTO1 protein is localized in the nucleus. The observation that AtSTO1 localizes in the nucleus is consistent with its proposed function as a transcription factor. AtSTO1-dependent phenotypes were observed when plant were grown at 50 mM NaCl on agar plates. Leaves of AtSTO1 overexpression lines were bigger with dark green coloration, whereas stunted growth and yellowish leaves were observed in wild-type and RNAi plants. Also, the AtSTO1 overexpression plants when exposed to long-term cold stress had a red leaf coloration which was much stronger than in wild-type and RNAi lines. Growth of AtSTO1 overexpression lines in long term under salt and cold stress was always associated with long roots which was more pronounced than in wild-type and RNAi lines. Proline accumulation increased more strongly in leaves and roots of AtSTO1 overexpression lines than in tissues of wild-type and RNAi lines when treated with 200 mM NaCl, exposed to cold stress or when watering was prevented for one day or two weeks. Also, soluble sugar content increased to higher levels under salt, cold and drought stress in AtSTO1 overexpression lines when compared to wild-type and RNAi lines. The increase in soluble sugar content was detected in AtSTO1 overexpression lines after long-term (2 weeks) growth of plants under these stresses. Anthocyanins accumulated in leaves of AtSTO1 overexpression lines when exposed to long term salt stress (200 mM NaCl for 2 weeks) or to 4°C for 6 and 8 weeks. Also, anthocyanin content was increased in flowers of AtSTO1 overexpression plants kept at 4°C for 8 weeks. Taken together these data indicate that overexpression of AtSTO1 enhances abiotic stress toleranc via a more pronounced accumulation of compatible solutes under stress.
Umweltstress wie zum Beispiel Trockenheit, Salz und niedrige Temperaturen beeinflussen in erheblichem Maße das pflanzliche Wachstum und haben einen negativen Einfluss auf Ertragsleistungen. Untersuchungen zur Verbesserung der Stresstoleranz und des Ernteertrages von Kulturpflanzen sind daher von großer Bedeutung. Pflanzen passen sich Umweltveränderungen durch physiologische und entwicklungsabhängige Prozesse an. In den letzten Jahren wurden zahlreiche Gene identifiziert, die als Reaktion von Umweltstress in der Pflanze aktiviert werden. Salzstress bewirkt negative Veränderungen des pflanzlichen Wasserstatus, die auf veränderte K+/Na+-Verhältnisse und Na+- und Cl--Konzentrationen zurückzuführen sind. Neben Veränderungen in der Bewässerungspraxis spielt heute die Züchtung salztoleranter Pflanzen und die biotechnologische Verbesserung von Kulturpflanzen eine zunehmend wichtige Rolle.
Im Rahmen der Doktorarbeit wurde ein bisher wenig untersuchtes Gen, welches AtSTO1 genannt wird, anhand der Modellpflanze Ackerschmalwand (lat. Arabidopsis thaliana) analysiert. Das Gen wird durch Umweltstress, insbesondere durch Kälte, aktiviert. Es wurden gentechnisch veränderte Pflanzen hergestellt, die eine verstärkte Aktivität des AtSTO1-Gens aufweisen. Diese Pflanzen zeigten bei Vorliegen von hohen Salzkonzentration ein im Vergleich zu unveränderten Pflanzen verbessertes Wachstum. Diese Stimulation des pflanzlichen Wachstums unter Salzstress-Bedingungen war begleitet von einer vermehrten Bildung bestimmter chemischer Substanzen, die die Pflanzen in die Lage versetzen, mit dem Stress besser fertig zu werden. Dazu gehört beispielsweise die Aminosäure Prolin, deren Konzentration in den gentechnisch veränderten Pflanzen nach Stressbehandlung stärker erhöht ist, als in den unveränderten Kontrollpflanzen oder in Pflanzen, die eine reduzierte AtSTO1-Aktivität besaßen. Auch die Gehalte einiger Zucker waren in den gentechnisch modifizierten Pflanzen unter Stress erhöht. Insgesamt hat sich gezeigt, dass AtSTO1 eine wichtige Aufgabe in der Stressantwort spielt. Weitere Untersuchungen sollten es ermöglichen, auch bei Kulturpflanzen, wie etwa Reis, die Stresstoleranz durch Veränderung verwandter Gene zu erhöhen.
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vollständiger Name des Autors: Abdallah Helaly, Alaa El-Din
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Tyrrell, John William. "Stress tolerance of transgenic alfalfa overexpressing glutathione reductase transgenes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ31872.pdf.
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Ma, Wai-lung, and 馬惠龍. "The role of stress tolerance on marine invasive mussels." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/196040.
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Marine bioinvasion has been increasing exponentially due to intensive human activities. To manage the threats posed by marine bioinvasion, it is important to understand the key factors for invasion success. Stress tolerance is thought to play an important role in the invasion process, however, little is known of the nature of this tolerance, particularly whether stress tolerance is species- or population-specific. To determine this, laboratory experiments were conducted to investigate differential tolerance of populations of a cosmopolitan marine invasive mussel, Perna viridis, and whether stress tolerance can be altered through pre-selection of individuals. Comparisons were firstly made between two local P. viridis populations from the intertidal and subtidal zones to test if stress tolerance was population-specific. Individuals from the intertidal population had higher baseline heart rates, lower critical salinity values, Scrit, for cardiac activity and longer survival duration at low salinity than individuals from the subtidal population, supporting the presence of population level differences in stress tolerance. Mortality of P. viridis was also compared at sites in both their introduced range (Hong Kong) and native range (Indonesia) which revealed that individuals from the Hong Kong population were more stress tolerant than their native counterparts in Indonesia. Using the same experimental approach, the effect of pre-selection to stress (a prior pre-selection to hypoxia and a subsequent exposure to heat) showed that stress tolerance can be enhanced by pre-selection. The second part of this study investigated whether invasive mussels, Brachidontes variabilis and P. virdis, were more stress tolerant than the native, non-invasive, Septifer virgatus. Laboratory experiments compared the Scrit as well as critical temperature, Hcrit for cardiac activity. Mortality and byssus thread production were also measured in a factorial design with different combinations of temperature (16, 24 and 32 °C) and salinity (8, 16, 32 p.s.u) for 15 days. The two invasive mussels had a higher Hcrit and lower Scrit, which indicated a higher stress tolerance, than the non-invasive mussel. The mortality rate of P. viridis was faster than in B. variabilis and S. virgatus at 8 p.s.u. whereas S. virgatus was the only mussel that exhibited mortality in the medium hyposalinity (16 p.s.u.) and showed much slower byssus attachment than the invasive mussels, suggesting that the invasive mussels are more stress tolerant to heat and medium hyposalinity than the non-invasive species. Overall, stress tolerance proved to be higher in the invasive than non-invasive species and was also population-specific with higher stress tolerance in the invasive population, which may be attributed to the selection of more tolerant individuals during the invasion process. Such a process may occur when founding individuals successfully pass through an invasion process, which may increase the overall mean population-level of stress tolerance and explain why invasive species are generally more stress tolerant than native species. Thus stress tolerance plays an important role in invasion success and invasive species with high stress tolerance may be favoured by climate change, including ocean warming and increased precipitation, which may extend their current distribution range.published_or_final_version
Biological Sciences
Master
Master of Philosophy
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Smith, Hilary April. "Evolution of Reproduction and Stress Tolerance in Brachionid Rotifers." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/52145.
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Stress can be a driving force for new evolutionary changes leading to local adaptation, or may be responded to with pre-existing, ancestral tolerance mechanisms. Using brachionid rotifers (microzooplankton) as a study system, I demonstrate roles of both conserved physiological mechanisms (heat shock protein induction) and rapid evolution of traits in response to ecologically relevant stressors such as temperature and hydroperiod. Rapid evolution of higher levels of sex and dormancy in cultures mimicking temporary waters represents an eco-evolutionary dynamic, with trait evolution feeding back into effects on ecology (i.e., reduced population growth). I also reveal that prolonged culture in a benign laboratory environment leads to evolution of increased lifespan and fecundity, perhaps due to reduction of extrinsic mortality factors. Potential mechanisms (e.g., hormonal signals) are suggested that may control evolvability of facets of the stress response. Due to prior studies suggesting a role of progesterone signaling in rotifer sex and dormancy, the membrane associated progesterone receptor is assayed as a candidate gene that could show positive selection indicating rapid divergence. Despite some sequence variation that may contribute to functional differences among species, results indicate this hormone receptor is under purifying selection. Detailed analyses of multiple stress responses and their evolution as performed here will be imperative to understanding current patterns of local adaptation and trait-environment correlations. Such research also is key to predicting persistence of species upon introduction to novel habitats and exposure to new stressors (e.g., warming due to climate change). Perhaps one of the most intriguing results of this dissertation is the rapid, adaptive change in levels of sex and dormancy in a metazoan through new mutations or re-arrangements of the genetic material. This suggests species may be able to rapidly evolve tolerance of new stressors, even if standing genetic variation does not currently encompass the suite of alleles necessary for survival.
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Watmough, Shaun A. "Adaptation to pollution stress in trees : metal tolerance traits." Thesis, Liverpool John Moores University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260825.
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O'Neil, John Daniel. "A molecular investigation of stress tolerance in aspergillus nidulans." Thesis, University of Wolverhampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273927.
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Jakkamsetty, Chamundeshwari, and Chaitanya Medapudi. "Stress tolerance of encapsulated yeast used for bioethanol production." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-9745.
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Environmental and economic issues have drawn the world’s attention to produce and utilize energy from renewable sources for sustainable development. One of the attempts includes the production of ethanol from various substrates. Many researchers have focused on utilizing lignocelluloses biomass as substrate for the production of ethanol, which mainly contains cellulose and is a cheap and abundantly available material in the world. One of the major problems faced by researchers during production of ethanol from the lignocellulosic biomass is the stress tolerance of yeast cells, due to the nature of the hydrolysed substrate (lignocellulosic material treated with Nitro methyl cellulose (NMC)). One of the solutions for this problem is to encapsulate the yeast cells. Encapsulation is an attractive method, which can enhance the stress tolerance of the yeast cells in the reactor, and also aid in maintaining a high yeast concentration inside the bioreactor and thereby increase the volumetric productivity of ethanol. This report includes a major study on the sodium chloride and ethanol stress tolerance of alginate chitosan alginate (ACA), alginate chitosan (AC) and APTES treated ACA encapsulated yeast biomass in medium containing different concentrations of glucose under anaerobic conditions. AC capsules shows significant results towards osmotic stress and ethanol stress compared with that of freely suspended cells in stress conditions.AC capsule encapsulated yeast tolerated osmotic stress better than ACA capsules in 2M of NaCl where as freely suspended yeast cells unable to tolerate 2M of NaCl . At 100th hour in AC capsules glucose consumption was 12 g/l where as in ACA capsules glucose consumption at same 100th hour was 2 g/l. At 10% ethanol concentration yeast inside ACA capsules showed 5 g/l of glucose consumption but in freely suspended yeast cells there is no glucose consumption as they cannot tolerate higher stress levels.
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Kuzovkina-Eischen, Yulia A. "Stress Tolerance and Horticultural Evaluation of the Genus Salix." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1047496264.
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Peyton, Justin Tyler. "Genomic Platforms and Molecular Physiology of Insect Stress Tolerance." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440175145.
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South, Kaylee. "Improving abiotic and biotic stress tolerance in floriculture crops." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1595499762154056.
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Brígido, Clarisse Cordeiro. "Tolerance of chickpea mesorhizobia to acid and salt stress." Doctoral thesis, Universidade de Évora, 2012. http://hdl.handle.net/10174/14546.
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The main objectives of this thesis were to evaluate the tolerance of a collection
of native Portuguese chickpea rhizobia to abiotic stresses, namely acidity and
salinity, and to investigate the molecular bases of acidity and salinity tolerance.
Additionally, the evaluation of the symbiotic performance of ACC deaminasetransformed
strains under salinity was performed. The involvement of the
chaperone ClpB in the response to abiotic stresses and in the symbiosis with
chickpea was investigated by gene deletion in a Mesorhizobium strain.
Chickpea rhizobia were assigned to several Mesorhizobium species. In both
stress conditions, tolerant and sensitive rhizobia were found, including
moderately acidophilic isolates. The analysis of the expression of the chaperone
genes dnaK and groESL suggests their involvement in acid tolerance. ACC
deaminase-transformed rhizobia strains showed an improvement of their
symbiotic performance under salinity. The characterization of the ClpB knockout
mutant indicated that ClpB is involved in the nodulation process; RESUMO:Os principais objetivos desta tese foram a avaliação da tolerância a stresses
abióticos, nomeadamente acidez e salinidade, de uma coleção de rizóbios
portugueses nativos de grão-de-bico, e investigar as bases moleculares da
tolerância a ambos os stresses. Adicionalmente, avaliou-se a eficiência
simbiótica de estirpes transformadas com o gene da ACC desaminase em
condições de salinidade. Investigou-se ainda o envolvimento da chaperone
ClpB na resposta a stresses abióticos e na simbiose com grão-de-bico através
da deleção do gene.
Os rizóbios de grão-de-bico pertencem a diferentes espécies de
Mesorhizobium. Encontraram-se rizóbios tolerantes e sensíveis a ambos os
stresses, incluindo isolados moderadamente acidófilos. A análise da expressão
dos genes de chaperones dnaK e groESL sugere o seu envolvimento na
tolerância à acidez. Estirpes de rizóbio transformadas com o gene da ACC
desaminase apresentaram uma melhoria da sua eficiência simbiótica em
condições salinas. A caracterização do mutante ClpB de Mesorhizobium
indicou que esta chaperone está envolvida no processo de nodulação.
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PATEL, VIJAY LAXMAN. "ARABIDOPSIS HSP21 AND MSRB1/MSRB2 IN PLANT STRESS TOLERANCE." Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/192201.
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Peththa, Thanthrige Nipuni. "Dissecting the molecular mechanisms of AtBAG4-mediated stress tolerance." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235369/1/Nipuni%2BPeththa%2BThanthrige%2BThesis%283%29.pdf.
Full textAbstract:
Plant biotechnology holds great promise to help meet the supply-demand gaps of agriculture to feed the future population. This thesis investigated the molecular mechanisms of stress tolerance conferred by the Arabidopsis thaliana Bcl-2 associated athanogene 4 (AtBAG4), cytoprotective protein. The research identified a role for AtBAG4 in several plant stress response pathways and further investigated the implications of expressing AtBAG4 in chickpeas. The AtBAG4-chickpea were equivalent to commercially available chickpea in non-stressed conditions but supported improved yields under drought. This knowledge will be used to develop improved chickpea varieties that tolerate stress without yield penalty.
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Groli, Eder Licieri <1988>. "Dissecting the Heat-Stress Tolerance QTLome in Durum Wheat." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9090/1/Groli_Eder%20Licieri_Tesi.pdf.
Full textAbstract:
Heat stress negatively affects wheat performance during its entire cycle, particularly during the reproductive stage. In view of the climate change and the prediction of a continued increase in temperature in the new future, it is urgent to concentrate efforts to discover novel genetic sources able to improve the resilience of wheat to heat stress. In this direction, this study addressed two different experiments in durum wheat to identify novel QTLs suitable to be applied in marker-assisted selection for heat tolerance. Chlorophyll fluorescence (ChlF) is a valuable indicator of plant response to environmental changes allowing a detailed assessment of PSII activity in view of its non-invasive measurement and high-throughput phenotyping. In the first study (Chapter 2), the Light-Induced Fluorescence Transient (LIFT) method was used to access ChlF data to map QTLs for ChlF-related traits during the vegetative growth stage in durum wheat under heat stress condition. Our results provide evidence that LIFT consistently measures ChlF at the level of high-throughput phenotyping combined with high accuracy which is required for Genome-Wide Association Study (GWAS) aimed at identifying genomic regions affecting PSII activity. The 50 QTLs identified for ChlF-related traits under heat stress mostly clustered into five chromosomes hotspots unrelated to phenology, a feature that makes these QTLs a valuable asset for marker-assisted breeding programs across different latitudes. In the second study (Chapter 3), a set of 183 accessions suitable for GWAS, was exposed to optimal and high temperature during two crop seasons under field conditions. Important agronomic traits were evaluated in order to identify valuable QTLs for GY and its components. The GWAS analysis identified several QTLs in the single years as well as in the joint analysis. From the total QTLs identified, 13 QTL clusters can be highlighted to be affecting heat tolerance across different years and/or different traits.
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Eakes, Donald Joseph. "Moisture stress conditioning, potassium nutrition, and tolerance of Salvia splendens 'Bonfire' to moisture stress." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54350.
Full textAbstract:
The objective of this study was to determine the leaf water relations, gas exchange, and growth of the bedding plant salvia Salvia splendens 'Bonfire‘ as influenced by moisture stress conditioning (MSC - exposing plants to 4 sublethal dry-down cycles) and potassium (K) nutrition. Plants were fertilized with one of six K rates: 25, 75, 150, 300, 450, and 600 ppm as KCl in experiment one. Seven weeks after seeding plants were subjected to MSC. MSC and increasing K rate resulted in osmotic adjustment and increased cellular turgor potentials. Foliar K content increased as osmotic potentials decreased due to treatment. Although there was no interaction, MSC and high K rates both reduced transpiration (E), leaf conductance (g₁), and daily gravimetric water loss during well watered conditions. Greatest shoot dry weight occurred for plants grown with 300 ppm K and no-MSC.
Gas exchange of salvia as influenced by MSC during the onset of moisture stress was determined in experiment two. On day one following final irrigation, MSC plants had lower mid-day E, g₁, hourly gravimetric water loss per unit leaf area, and net photosynthesis (Pn) compared to controls, despite no differences in leaf water potential (ψ₁). Percentage of stomatal inhibition of Pn (SI) was greater for MSC plants than controls with no differences in mesophyllic resistance to CO₂ (rm). On day two, MSC plants had greater Pn, E, g₁, and hourly gravimetric water loss per unit leaf area, while SI and rm were lower than controls. MSC plants maintained positive Pn rates and turgor to lower ψ₁ than control plants. Water use efficiency (WUE) estimates for MSC plants were greater than for controls.
Salvia plants were fertilized with 75, 300, or 600 ppm K to determine the influence of K rate on gas exchange during the onset of moisture stress in a third experiment. On day one following final irrigation, plants grown with K rates of 300 and 600 ppm had lower E, g₁, hourly gravimetric water loss per unit leaf area, and Pn compared to 75 ppm K plants. On day two, 600 ppm K plants had greater Pn, E, and g₁ as the experiment was terminated compared to plants grown with 75 ppm K, although ψ₁ was similar. Potassium rate had little affect on WUE.Ph. D.
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Barker, Clive. "The survival of Listeria monocytogenes during acid stress." Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342154.
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Dewey, Daniel Wade. "Physiological and genetic control of water stress tolerance in zoysiagrass." Texas A&M University, 2005. http://hdl.handle.net/1969.1/3172.
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Significant cultivar difference in many water stress responses of zoysiagrass
(Zoysia japonica (Steud.) and Zoysia matrella (L.) Merr.) are shown in this study. Of the
four cultivars, Palisades was the most water stress tolerant, had the most negative turgor
loss point, and leaf rolled after loss of full turgor pressure. On the other end of the
spectrum, Diamond was the least water stress tolerant, had the lowest full turgor pressure,
the least negative turgor loss point, and leaf rolled at full turgor. Differences between
Diamond, Cavalier, Palisades, and DALZ 8504 in leaf rolling, loss of full turgor, water
release curve parameters, root characteristics and gene expression make zoysiagrass a
prime candidate for further investigation into the mechanisms of water stress
avoidance/tolerance. Enhanced antioxidant activity and stomatal control, along with root
characteristics, most likely explain the cultivar difference in water stress tolerance of
zoysiagrass. Palisades and DALZ 8504 maintained full turgor for significantly longer
than Diamond and Cavalier, which may be associated with root characteristics and/or
enhanced stomatal control as only those two cultivars showed enhanced expression of a
stomatal control gene (phospholipase D). The apparent response (most apparent in turgid
weight/dry weight ratios (TWDW)) of well watered plants to water stressed neighbor plants will likely be the most novel finding of this study. Well watered zoysiagrass and
Kentucky bluegrass responded to water stressed neighbors by reducing TWDW.
Significant increases in gene expression of a systemin degrading enzyme and of an
integral membrane protein (signal receptor) were also observed in well watered plants.
Results from this study indicate that this phenomenon is occurring and expose a dearth in
scientific understanding that must be filled. Improving water stress tolerance through
breeding for parameters like those discussed in this paper (delayed leaf rolling or loss of
full turgor, enhanced stomatal control, enhanced antioxidant activity, deep rooting
characteristics, etc.) may very likely produce turfgrasses that can survive and maintain
desired aesthetic qualities using significantly less water.
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Pahkala, Maarit. "Evolutionary ecology of ultraviolet-B radiation stress tolerance in amphibians." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5081-4/.
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Mohammady-D, Shahram. "Inheritance of tolerance to water-stress in wheat (Triticum aestivum)." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250130.
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Panaretou, Barry. "The plasma membrane in the tolerance of yeast to stress." Thesis, University College London (University of London), 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437063.
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Moore, Thomas. "Are barley dwarfing genes important in tolerance to abiotic stress?" Thesis, University of East Anglia, 2012. https://ueaeprints.uea.ac.uk/42362/.
Full textAbstract:
DELLA proteins are a highly conserved group of growth inhibitors, mutants of which were integral to the semi-dwarf, high yielding wheat lines of the Green Revolution. In addition to reducing plant growth, the gain of function (GoF) mutants in which DELLA protein is stabilised were shown to confer resistance to salt stress in the model species Arabidopsis. In order to determine whether these findings could be translated from Arabidopsis to monocot crop species, GoF and loss of function (LoF) mutants of the barley DELLA orthologue, Sln1, were characterised and growth and development assessed. By subjecting DELLA wild-type and mutant barley plants to abiotic stress conditions (salt stress and heat shock) it was established that the increased survival conferred by stabilised DELLA that was reported in Arabidopsis was also applicable to barley, and that survival of the LoF barley mutants was decreased. Further evidence for the importance of stabilised DELLA was obtained when additional mutants in the GA signalling pathway (gse1a,j,n; Gse1, GA receptor mutants) in which DELLA protein is predicted to accumulate, also showed increased tolerance to abiotic stress. These data suggest DELLA protein function is conserved between monocot (cereal) and dicot plants. Attempts to produce transgenic barley plants in which Sln1 was silenced were inconclusive, likely underlining the essential nature of the gene in growth, development and regeneration. The studies provide a basis for further work to investigate the mechanisms underlying DELLA function in cereals.
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Rajab, Salem Mohamed Ahmed. "The role of HvBWMK1 in barley tolerance to abiotic stress." Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/2830.
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Barley (Hordeum vulgare L.) is an important crop grown throughout the world. Quality and quantity of barley is compromised by abiotic stresses, salinity in particular which is already widespread in many regions. Mitogen Activated Protein Kinase (MAPK) cascades are signal transduction pathways involved in biotic and abiotic plant defence mechanisms. Here, the function of the barley gene HvBWMK1 has been investigated. Transgenic barley plants that overexpress HvBWMK1, or in which HvBWMK1 has been down-regulated by antisens, were generated, as well as empty vector control plants. The transformation efficiency using Agrobacterium was 10.4% independent transgenic plant per embryo. Northern blot analysis of HvBWMK1 primary overexpression lines showed up-regulation of mRNA level, conversely the antisense lines of HvBWMK1 showed clear down-regulation. Real-time PCR analysis in the T1 generation revealed that two over-expresser lines showed higher expression as compared with wild type (by 79% and 35%) while the HvBWMK1 antisense construct reduced endogenous gene expression partially (by 14%, 23% and 39% compared with wild type). Barley seedlings were subjected to two weeks of salt stress (150 mM NaCl) then biochemical and physiological parameters were measured. The overexpression lines showed an increase in tolerance to salinity stress compared to antisense lines and controls. Tolerance was accompanied with increasing endogenous proline and chlorophyll levels and a reduction in hydrogen peroxide content after salinity exposure. Overall these results suggest that the barley MAPK HvBWMK1 acts as a positive regulator in barley tolerance to salinity stress.
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Chilufya, Jedaidah, Kousha Mohensi, and Aruna Kilaru. "The Role of Anandamide in Biotic Stress Tolerance in Mosses." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/4843.
Full textAbstract:
Mosses are small avascular bryophytes with a haploid dominant gametophyte and a diploid sporophyte stage. The gametophyte cells are single layered and lack a protective cuticle, which is the first line of defense in vascular plants. These factors would render them highly susceptible to stress but on the contrary, mosses have flourished on land for the past 450 million years with tolerance to both abiotic and biotic stress. Occurrence of unique lipids in bryophytes was considered as an adaptive means to survive harsh terrestrial condition. A recent study identified a lipid metabolite, anandamide in the Physcomitrella patens. Anandamide (NAE 20:4) belongs to a group of fatty acid ethanolamides or N –acylethanolamines (NAEs). In eukaryotes, NAEs were shown to play an important role in mediating stress responses. In plants, NAE 14:0 has been implicated in biotic stress response; its levels increased up to 50-fold in elicitor-treated tobacco plants, along with induction of defense gene expression and inhibition of alkalization. In animals anandamide acts as an endocannabinoid ligand and mediates several physiological responses including stress. This study aims to use P. patens as the model system because of its available genomic database and prior studies on biotic stress, to examine if NAE 20:4 contributes to their ability to tolerate biotic stress. It is hypothesized that the occurrence of anandamide will play a role in mediating biotic stress tolerance in P. patens. To test this hypothesis, three specific aims are proposed. They are to determine the effect of 1) elicitor-treatment on NAE and fatty acid profile in the moss, 2) anandamide on elicitor-induced morphological and physiological changes in the moss and 3) anandamide on elicitor-induced defense gene expression in moss. Mosses utilize similar defense mechanisms as flowering plants and disease symptoms can easily be studied using microscopy because of their haploid dominant gametophyte stage with monolayer cells. The induction of defense gene expression will be studied by quantitative PCR and changes in lipid profile by selective lipidomics. This study is expected to provide novel insights into the role of anandamide in early land plants, specifically in response to biotic stress.
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Manuel, Theodore Llewellyn. "Effect of soil nutrient status on stress tolerance in Proteaceae." Bachelor's thesis, University of Cape Town, 1988. http://hdl.handle.net/11427/25615.
Full textAbstract:
Protea lepidocarpodendron grown on low, medium and high nutrient treatments exhibited the lowest, and similar evapotanspiration rates respectively over a 9 day water stress cycle (experimental period). In stressed and unstressed treatments, stomatal conductance and transpiration rates of plants grown on the low nutrient treatment was generally lower than that of plants grown on the medium and high nutrient treatments where stomatal conductance and transpiration rates were similar. Stressed plants grown on the low, medium and high nutrient treatments exhibited the lowest, intermediate and highest photosynthetic rates respectively. Stessed plants grown on the medium and high nutrient treatments exhibited a dramatic decrease in transpiration rates ands stomatal conductance from day 5 to 7, and a dramatic decrease in photosynthetic rates from day 3 to 7. Stressed plants grown on the low nutrient treatment showed a far less dramatic decrease in transpiration rate, stomatal conductance and photosynthetic rate over the 9 day period. For stressed plants, photosynthetic rates varied between 0.08-5.39 uMOLm⁻²s⁻¹, 1.17-7.48uMOlm⁻²s⁻¹ and 1.15-8.65uMOLm⁻²s⁻¹ for plants grown on low, medium and high nutient treatments respectively. Unstressed plants grown on low. medium and high nutrient treatments exhibited the lowest, highest and intermediate photosynthetic rates respectively. In all stressed treatments, photosynthetic rates showed a steady decline from day 1 to day 7, whereafter a dramatic increase occurred in the medium and high nutrient treatments, and a less dramatic increase in plants grown on the low nutrient treatment. These decreases and increases in photosynthetic rates was not parallelled in the stomatal conductance and transpiration rates of the unstressed plants. For unstressed plants, photosynthetic rates varied between 1.4s-4.4 uMOLm⁻²-s⁻¹, 1.65-6.7 uMOLm⁻²s⁻¹ and 3.42-8.76 uMoLm⁻²s⁻¹ for plants grown on low, medium and high nutrient treatments respectively. Plants grown on low nutrient treatments exhibited the highest LSW (182.3 gm⁻²), highest whole plant mass (WPM) (1.07g), followed by high (LSW=1.76 gm⁻²,WPM=0.83g) and medium (LSW=167.28 gm⁻² ,WPM=0.79g) nutrient treatments. Total plant nitrogen content was inversely related to LSW and WPM on low (3.84 mgNplant⁻¹), high (4.18 mgNplant⁻¹) and medium (5.28 mgNplant⁻¹) treatments. Root : ratio between treatments were similar.
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Elnitsky, Michael A. "Tolerance and Physiological Response to Environmental Stress in Antarctic Arthropods." Miami University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=miami1216152581.
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Li, Aiqing. "Identification Of Proteins Associated With Insect Diapause And Stress Tolerance." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1211487603.
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Teets, Nicholas Mario. "Cellular and Molecular Mechanisms of Environmental Stress Tolerance in Insects." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1354542991.
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Janislampi, Kaerlek W. "Effect of Silicon on Plant Growth and Drought Stress Tolerance." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1360.
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Silicon is not considered an essential nutrient, but it is typically abundant in soils and can be taken up in large amounts by plants. Silicon is known to have beneficial effects when added to rice and several other plants. These effects include disease and insect resistance, structural fortification, and regulation of the uptake of other ions. In this study, the effect of silicic acid fertilization on the growth and drought tolerance of four crop plants (corn, wheat, soybean, and rice) was analyzed. Plants were studied using three cultivation techniques: 1) hydroponic solution and subjected to salt stress, 2) low-silicon soil-less medium (peat) and subjected to gradual drought stress, and 3) low-silicon soil-less medium (peat) and subjected to acute drought stress. Silicon was added both as reagent-grade Na2SiO3 and as a siliceous liming agent (PlantTuff). Both forms of Si generally improved drought and salt stress tolerance, but the effects were inconsistent. Silicon increased corn dry mass by up to 18% and the effect was statistically significant (p<0.05) in two out of three techniques. Silicon increased water use efficiency in corn by up to 36% and the effect was statistically significant (p<0.05) in one out of two techniques. In the acute drought stress technique, silicon increased wheat dry mass by 17% and the effect was statistically significant (p<0.05). Silicon increased soybean and rice dry mass by 20 to 30%, but the effect was not statistically significant. Silicon in oldest corn leaves increased from 0.4% to 3% as Si increased from less than 0.01 to 0.8 mM in the hydroponic solution. There was a statistically significant effect of silicon supply on the concentration of some other nutrients, but the effect was often not great enough to be considered biologically important. Rice accumulated the greatest concentration of foliar silicon, corn and wheat were intermediate, and soybean accumulated the least. Collectively, these results indicate an effect of silicon in drought and salinity stress tolerance, but additional studies on the rate and onset of drought are needed to determine interacting factors and better understand the inconsistent results.
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Karim, Sazzad. "Exploring plant tolerance to biotic and abiotic stresses /." Uppsala : Dept. of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, 2007. http://epsilon.slu.se/200758.pdf.
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ADAMO, GIUSY MANUELA. "Evolution of copper tolerance in yeast cells." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2012. http://hdl.handle.net/10281/29458.
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For all living organisms, copper (Cu) is an essential micronutrient taking part, with its redox chemistry, to several metabolic and regulatory cellular events. However, the same redox properties that make Cu essential are responsible for its toxicity. Indeed, Cu participates in reactions that generate Reactive Oxygen Species (ROS). ROS target main cellular macromolecules (proteins, lipids, DNA and RNA), leading to cellular dysfunctions and in the extreme case, to cell death. All living organisms evolved molecular mechanisms for Cu homeostasis. Indeed, uptake, transport and detoxification systems that actively prevent both Cu deficiency and poisoning are well conserved along the phylogenetic tree. Among eukaryotes, these mechanisms have been mainly investigated in the yeast Saccharomyces cerevisiae used as a model organism.
Evolutionary engineering is a rational approach that uses the evolutionary principles to direct the selection of organisms with a desired set of phenotypes, allowing for the improvement of microbial properties. This approach can be exploited to obtain Cu-tolerant and Cu-accumulating yeast cells, with potential application in nutraceutics, as nutritional supplements, as well as in bioremediation, for the removal or recovery of metal ions. At the same time, evolutionary engineering is a valuable strategy to gain more insight into the molecular aspects of Cu tolerance in microbial cells.
In the present work is described an evolutionary engineering strategy to improve Cu tolerance of natural yeasts. Strains of Saccharomyces cerevisiae and of Candida humilis originally endowed with different sensitivity and tolerance toward Cu have been exposed to increasing concentrations of Cu during cell cultivation in liquid medium. This treatment stably improved Cu tolerance of all strains. One evolved strain for each yeast species was then chosen to analyze in detail the physiological response to Cu. Compared with the original Cu-sensitive strains the two evolved strains showed improved cell viability and attenuated production of ROS. A reshaping of the profile of antioxidant enzymes and Cu-binding proteins was observed in both strains as a specific response to copper.
Further investigations carried out on S. cerevisiae strains demonstrated a pivotal role of the CUP1 gene, encoding for a metallothionein. A 7-fold amplification of this gene was found associated with evolution of Cu tolerance.
Finally, Cu tolerance in C. humilis cells was studied by proteomic analyses. Changes were observed in the levels of several proteins involved in the oxidative stress response (such as glycolytic enzymes), heat shock proteins, proteins involved in protein synthesis and energy production, proteins with a role in phospholipids synthesis. Cu exposure resulted in differential protein expression, in both non-evolved and Cu evolved cells. In general, changes in protein levels detected in evolved cells were smaller. On this basis, it was hypothesized that in the evolved cells copper tolerance relies only partly on the molecular mechanisms associated with the oxidative stress response. This work shows once again that evolutionary engineering is a powerful strategy to drive the gain of stable phenotypic traits. The evolved strains might found direct application in several biotechnological fields, and provide a kind of “molecular platform” for the investigation on the mechanisms of stress tolerance. The availability of data about the S. cerevisiae genome allowed a focused investigation on the molecular actors involved in Cu tolerance. In the case of C. humilis, the use of a proteomic approach allowed to compensate for the poor information available on the determinants of Cu tolerance.
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Bonomo, Jeanne M. "Metabolic engineering tolerance to amino acid related stress in Escherichia coli." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/cr/colorado/fullcit?p3190379.
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Al-Quraan, Nisreen Singh Narendra K. "Role of Arabidopsis thaliana calmodulin isoforms in tolerance to abiotic stress." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SUMMER/Biological_Sciences/Dissertation/Al-quraan_Nisreen_3.pdf.
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Meek, Haley. "Seed Coat Pigment Variation and UV Stress Tolerance in Lupinus perennis." Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1542386060563396.
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Goy, Jo M. "Aging Is a Determinant in Anoxia Stress Tolerance in Caenorhabditis Elegans." Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc271821/.
Full textAbstract:
Oxygen availability is critical for survival for most organisms. The nematode, C. elegans, has been useful for studying genetic regulation of anoxia tolerance due to the oxygen deprivation response mechanisms shared with other metazoans. Studies examining long-term anoxia (72h, LTA) tolerance have only been conducted at adult day 1. To investigate the effect of aging on anoxia tolerance wild-type and mutant strains were exposed to LTA between adult day 1 and day 9. Wild-type isolates and daf-16(mu86) (FOXO transcription factor regulated by insulin-signaling) and aak-2(gt33) (catalytic subunit of AMP-activated protein kinase) strains were anoxia sensitive at day 1 and displayed increased LTA tolerance with aging correlated with reproductive senescence followed by a decline in survivorhsip through day 9. The daf-2(e1370) (insulin receptor homologue of C. elegans), glp-1(e2141) (a lin-12/Notch receptor) and fog-2(q71) (required for spermatogenesis) strains were LTA-tolerant through day 5. I conclude that aging influences LTA-tolerance in a strain- and age-dependent manner. In addition to being LTA-tolerant the daf-2(e1370) and glp-1(e2141) strains have a longevity phenotype that is suppressed by loss of kri-1 or daf-12. While loss of kri-1 did not suppress the LTA-tolerant phenotype of glp-1(e2141) at day 1 the portion of impaired survivors increased at day 3 and by day 5 tolerance was suppressed. Similarly, when exposed to 4 days of anoxia the glp-1(e2141);daf-12(rh41rh611) double mutant had a reduced survivor rate at all ages analyzed compared to glp-1(e2141) controls. To better understand formation of an anoxia-tolerant physiology I exposed adults to one or more 24h bouts. Recurrent bouts increased LTA tolerance in wild-type hermaphrodites in a dose-dependent manner. Bout-treated daf-16(mu86) animals had increased survival rate compared to controls yet maximum survival remained below age-matched wild-type. Anoxia bouts decreased LTA-tolerance in aak-2(gt33) mutants, indicating the requirement for ATP regulation in establishing an LTA-tolerant phenotype. These data support the idea that anoxia tolerance is multi-factorial and influenced by environment, metabolism, food, reproduction, sex phenotype and likely additional factors.
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Johnson, Stephanie. "The mechanisms of drought stress tolerance in the crop Sorghum bicolor." Thesis, Durham University, 2016. http://etheses.dur.ac.uk/11426/.
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Drought stress can have a major impact upon plant survival and crop productivity. Sorghum bicolor is an important cereal crop grown in the arid and semi-arid regions of >98 different countries. It is well adapted to the harsh drought-prone environments in which it is grown however; relatively few studies have investigated the molecular basis of these adaptations. Breeding programs have lead to the identification of ‘stay-green’ varieties, so-called due to their ability to maintain green photosynthetic leaf area for longer under drought conditions. However, despite extensive breeding efforts to select for this trait we have very little understanding of the fundamental biological processes that underlie it. Microarray analysis was used to identify gene expression changes in sorghum following heat stress, drought stress and combined heat and drought stress. These microarrays were additionally used to compare gene expression in stay-green (drought-tolerant) and senescent (drought-sensitive) sorghum lines. Ontological analysis of the genes expressed to higher levels in the stay-green lines identified key processes hypothesised to be associated with the trait. These include genes associated with proline and betaine biosynthesis, glutathione S-transferase (GST) activity and the regulation of stomatal aperture and density. Both proline levels and GST activity were found to be higher in the stay-green lines thus validating that the changes at the gene expression level result in changes at the protein level. Stay-green lines were also shown to have reduced transpiration and reduced numbers of stomata. Two signalling genes, DREB1A and SDIR1 were expressed to higher levels in the stay-green varieties. Transgenic lines overexpressing these genes were generated in order to test their function. Based on the gene expression data, putative mechanisms underlying two QTL for the stay-green trait (Stg1 and StgB) were generated. Further validation of these genes and processes could not only improve our understanding of drought tolerance mechanisms in sorghum, but also facilitate the improvement of future sorghum cultivars.
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Myers, Jonathan Andrew. "Seedling carbohydrate storage, survival, and stress tolerance in a neotropical forest." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0009262.
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Siriwardena, P. P. G. S. N. "Tolerance and early life stages of Tilapia (Cichlidae:Tilapiini) to metal stress." Thesis, University of Stirling, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384838.
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