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1
Potts, Malcolm. "Desiccation tolerance." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/9528/.
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Despite the fundamental significance of desiccation in determining the distributions and activities of living organisms, there is virtually no insight as to the state of the cytoplasm of an air-dried, or even a wet, cell. In bacterial cells that have been subjected to air-drying the evaporation of free cytoplasmic water (Vf) can be instantaneous, and an equilibrium between cell-bound water (VQ and the environmental water (vapor) potential (Ψwv)) may be achieved very rapidly. In the air-dried state some bacteria survive only for seconds, others can tolerate desiccation for thousands, perhaps for millions, of years. The means by which certain cells, the anhydrobiotes, overcome and then tolerate acute water deficit remains one of the most intractable problems in cell biology. One such anhydrobiote, the cyanobacterium Nostoc commune, is cosmopolitan, its colonies form visually-conspicuous and abundant growths in situ, and it constitutes an ecologically-significant component of terrestial nitrogen-fixing communities. The cyanobacteria are phylogenetically-significant organisms that provide model systems for the study of a broad range of problems in cell biology. The studies described in this thesis established the molecular ecology and cell biology of Nostoc commune, and they provide a chronicle of the development of this microorganism as the prokaryotic model for the anhydrobiotic cell. In the design of experiments to investigate this problem the bias was, and remains, this: to understand desiccation tolerance, understand an organism that tolerates desiccation. The thesis documents an investigation into the consequences of acute cell-water deficit and the cellular basis for desiccation tolerance. An eclectic approach has been adopted to study desiccation tolerance and it includes the application of techniques of cell biology, biochemistry, microbiology, molecular biology, structural biology and biophysics.
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Chaibenjawong, Plykaeow. "Desiccation Tolerance in Staphylococcus aureus." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522502.
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Dace, Halford. "Metabolomics of desiccation tolerance in Xerophyta humilis." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/9111.
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Includes bibliographical referencesResurrection plants are unique in the ability to survive near complete water loss in vegetative tissues without loss of viability. In order to do so, they employ multifaceted strategies which include structural adaptations, antioxidant and photoprotective mechanisms, and the accumulation of proteins and metabolites that stabilise macromolecules. A full understanding of the phenomenon of vegetative desiccation tolerance will require a systems view of these adaptations at the levels of the genome, the control of gene expression, and the control of metabolic pathways. This dissertation reports a high-throughput metabolomic analysis of the changes that occur in vegetative tissues of resurrection plant Xerophyta humilis during dehydration. A combination of chromatography, mass spectrometry and nuclear magnetic resonance revealed numerous primary and secondary metabolites in the plant. Multivariate statistics identified a subset of metabolites that were significantly up- or down-regulated in response to water deficit stress. These metabolites both confirmed existing observations about the metabolic response of X. humilis to drying and revealed compounds not previously known to be associated with this response. Desiccation-associated metabolites were mapped onto known biochemical pathways, to generate hypotheses concerning possible regulatory schemes in the stress response, inviting deeper investigation in future.
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Casteriano, Andrea Veronica. "Physiological mechanisms of desiccation tolerance in Rhizobia." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/10423.
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One of the main factors affecting the survival of rhizobia on seed is desiccation stress. The poor survival of rhizobia affects nodulation, nitrogen fixation and legume yield. A better understanding of desiccation tolerance and how it may be enhanced may contribute to the development of strategies to improve survival of rhizobia on seed. This study aimed to improve the survival of rhizobia by enhancing inherent mechanisms of desiccation tolerance through the manipulation of the growth medium. Accumulation of intracellular trehalose by rhizobia increases in response to osmotic and desiccation stress, and has also been related to an improved capacity for desiccation tolerance. In this study, a linear relationship was observed between intracellular trehalose accumulation in Rhizobium leguminosarum bv. trifolii (TA1) and Bradyrhizobium japonicum (CB1809) and increasing osmotic pressure of a defined growth medium (JMM) from 1.0 atm to 2.8 atm. Although increased concentrations of intracellular trehalose did not improve survival of rhizobia immediately after vacuum drying, survival was significantly improved after 10 days of storage at low relative humidity (9%). Resuspending rhizobia in trehalose solution, to provide external protection to cells during drying, significantly increased survival immediately after drying and storage. The increased protection during drying allowed the positive effect of intracellular trehalose on rhizobial survival to be observed. Cells of TA1 and CB1809 extracted from peat after solid-state fermentation survived significantly better immediately after vacuum drying (22-fold and 5-fold respectively) and during storage than cells grown in JMM (1.0 atm). However, it was difficult to extract adequate V cell mass to measure intracellular trehalose and consequently cells were grown in water extracts of peat to simulate the conditions that rhizobia would be exposed to in traditional peat cultures. Growing TA1 and CB1809 in aqueous peat extract increased trehalose accumulation compared to cells grown in JMM and also significantly improved survival (18-fold) of TA1. Although survival of CB1809 was generally improved after growth in peat extract, it was not significantly different to cells grown in JMM. Cells grown in peat extract exhibited changes in cell morphology and protein expression similar to those observed after solid-state fermentation in peat. Electron microscopy revealed the accumulation of an electron-dense material around the plasma membrane that occupied the periplasmic space in both TA1 and CB1809. Similar changes to cell morphology have been previously linked to improved survival. Peptide analysis by liquid chromatography-mass spectrometry indicated increased expression of stress response proteins in TA1 and CB1809 after growth in peat extract. Some of those proteins included membrane repair proteins (PspA) and proteins generated to combat periplasmic stress (OstA) and oxidative damage (thioredoxin). A cell viability assay using alamarBlue® reagent showed that growing rhizobia in peat extract reduces metabolic activity compared to that of cells grown in JMM, and membrane integrity analysis of the same cells using a LIVE/DEAD® viability kit showed that peat extract increased membrane permeability to propidium iodide (PI). Environmental stresses have been reported to cause reversible changes to membrane function and permeability, demonstrated by changes in PI-uptake. This finding, together with the changes in cell morphology and increased expression of stress response proteins, suggests that improved survival after growth of rhizobia in peat extract is related to adaptive changes of cells in response to water-extractable constituents of peat. VI Findings from this work suggest that desiccation tolerance in rhizobia is a multifactorial process that involves the accumulation of trehalose together with the expression of proteins involved in maintaining cell envelope integrity and stability, as well as the repair and prevention of DNA and protein damage caused by oxidative stress. Determining chemical elicitors of adaptive changes in cells may assist in further development of inoculant technology to improve survival of rhizobia on seed.
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Fleming, Erich David. "Responses of desiccation-tolerant cyanobacteria to environmental extremes /." view abstract or download file of text, 2006. http://wwwlib.umi.com/cr/uoregon/fullcit?p3211215.
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Thesis (Ph. D.)--University of Oregon, 2006.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 115-129). Also available for download via the World Wide Web; free to University of Oregon users.
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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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Montazeri, Mansoor. "Desiccation tolerance as a factor in mycoherbicides pathogenicity." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289535.
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Ratnakumar, Sooraj. "Molecular mechanisms of desiccation tolerance in Saccharomyces cerevisiae." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612298.
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Jones, Stephen Keith. "Sitka spruce (Picea sitchensis [Bong.] Carr.) seed germination in relation to seed development, dormancy and storage." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283746.
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Lyall, Rafe. "Regulation of desiccation tolerance in Xerophyta seedlings and leaves." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22853.
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A small, diverse group of angiosperms known as resurrection plants display vegetative desiccation tolerance and can survive loss of up to 95% of cellular water, a feat only seen in the seeds and pollen of other angiosperms. Xerophyta humilis is a resurrection plant native to Southern Africa that has been the target of previous transcriptomic and proteomic studies into the mechanisms of plant desiccation tolerance. The aim of this study was to investigate the hypothesis that vegetative desiccation tolerance is derived from the networks that control desiccation tolerance in seeds and germinating seedlings in angiosperms, particularly the epigenetically silenced seed maturation genes. Germinating seedlings of X. humilis and the related resurrection plant X. viscosa were found to be VDT from the earliest stages of germination, and exhibited the characteristic vegetative trait of poikilochlorophylly as seen in mature leaves. The X. humilis desiccation transcriptome comprising 76,768 distinct gene clusters was successfully assembled from sequencing samples at five relative water contents (100%, 80%, 60%, 40% and 5%) to identify the networks activated in response to water loss. Desiccation was associated with successive waves of transcription factor induction, as well as widespread down-regulation of histone modification enzymes. Many seed-specific genes, such as late embryogenesis abundant (LEA) proteins, seed storage proteins and oleosins, were induced in vegetative tissue. LEA transcripts in particular were highly up-regulated during desiccation, and the large number of distinct LEA transcripts (over 150) suggests possible LEA gene expansion in Xerophyta compared to desiccation-sensitive plants. Components of the PYL/SnRK2/ABF ABA-signalling pathway were also induced, although the ABF transcription factors activated in response to desiccation were most similar to those induced by drought in A. thaliana rather than seed maturation. Of the canonical seed master regulators (such as the LEC1/ABI3/FUS3/LEC2 network and ABI5) only three ABI3 transcripts were expressed, all of which encoded proteins lacking the seed motif-binding B3-domain. The results of this study suggest that vegetative desiccation tolerance in X. humilis is not associated with re-activation of seed master regulators in vegetative tissue, but may instead involve activation of seed genes by vegetative drought response regulators.
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Madden, Christine Frances. "Eragrostis nindensis: unravelling senescence in an African desiccation tolerant grass." Doctoral thesis, Faculty of Science, 2019. https://hdl.handle.net/11427/31652.
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Food security is one of the most important global challenges facing the world today, especially in the context of climate change. Research has been conducted into a unique group of plants, called “resurrection plants”, that can withstand up to 95% tissue water-loss without compromising viability by, inter alia, undergoing extensive metabolic reprogramming and suppressing senescence. In this thesis the African desiccation tolerant grass Eragrostis nindensis (Fical & Hiern) was used as a model plant to identify which biological processes are unique to senescence and critical for desiccation tolerance. When desiccated, the older leaves of E. nindensis senesce, whereas, the younger leaves recover fully upon rehydration, thereby displaying two phenotypes in a single species. Comparing these two tissue types can show how senescence upon abiotic stress is regulated. Differences in transcript abundances between the two tissue types during drying and rehydration was analysed through RNA-seq analysis, coupled with physiological quantitative traits, mass spectrometry analyses and immunoblotting. The transcriptome reflected a transcriptomic reprogramming towards desiccation tolerance by maintaining transcription of genes that control desiccation tolerance traits in both tissue types, however, only the desiccation tolerant (non-senescent) tissue appeared to suppress senescence and maintained translational control. It was hypothesised that the non-senescent tissues regulate and stabilise RNA. The older tissues were unable to suppress senescence, which resulted in cell death. Lipids accumulated in the non-senescent tissue, particularly unsaturated triacylglycerols. It was proposed that lipid droplets that accumulated during drying were stabilised through, in part, the protein expression of oleosin. These lipid droplets appeared to provide a mechanical stabilisation and energy-providing role in the non-senescent tissue. The transcription of genes that control desiccation tolerance traits was generally maintained in both tissue types, however, translation was prevented in the senescent tissue. The non-senescent tissue therefore appeared to engage in a regulation of senescence at the translational level, rather than a fine-tuned transcriptional regulation. The aim of this work was to provide a critical baseline for future studies working on E. nindensis, and desiccation tolerance and senescence in resurrection plants in general. Ultimately, understanding water-deficit stress in the context of senescence can help to improve drought resistance in crops to ensure food security, particularly in Africa.
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Wright, Deborah J. "Molecular Biology of Desiccation Tolerance in the Cyanobacterium Nostoc commune." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/9714.
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The molecular biology of desiccation tolerance was investigated in the cyanobacteria with emphasis on Nostoc commune. Analysis of DNA from 41 samples of desiccated Nostoc spp. of varied age and global distribution led to the amplification of 43 independent tRNALEU(UAA) group 1 intron sequences. Phylogenetic analysis of the entire data set made it possible to define the form species Nostoc commune.
The synthase (spsA) and phosphatase (sppA) genes required for the synthesis of sucrose were isolated from cyanobacterium Synechocystis sp. strain PCC 6803 and overexpressed in E. coli in two different vector constructions. Transformants had a marked increased capacity for desiccation tolerance. Sucrose synthesis was confirmed through thin layer chromatography (TLC) analysis of cell extracts from transformants.
Long-term stability of DNA in desiccated Nostoc samples was demonstrated by the ability to amplify selected gene loci from samples stored dry for decades. Successful amplification in some samples was possible only after treatment with phenacylthiazolium bromide, a reagent that disrupts covalent cross-links; indicating that the DNA was modified by cross-links that occurred between reducing sugars and the primary amines on the DNA.
Abundant superoxide dismutase was released following rehydration of desiccated field material N. commune CHEN after 13 years in the dry state. sodF mRNA was present in the dry material but was turned over within 15 min of rehydration. mRNA levels then rose and appeared to reach steady state levels after 3 hours and remained abundant after 24 hours of rehydration.Master of Science
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Mulat, Teshome G. "Chemical desiccation tolerance and nonstructural carbohydrate dynamics in winter wheat." Access citation, abstract and download form; downloadable file 3.70 Mb, 2004. http://wwwlib.umi.com/dissertations/fullcit/3131690.
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Dzobo, Kevin. "Characterization of polyphenols in leaves of four desiccation tolerant plant families." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/4256.
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Includes bibliographical references.Polyphenols in plants are known to act as antioxidants, antimicrobials, antifungal, photoreceptors, visual attractors and as light screens. In this study polyphenols in angiosperms found in southern Africa and called resurrection (desiccation tolerant) plants were studied. These plants are Myrothamnus flabellifolius, Xerophyta viscosa, Xerophyta humilis, Xerophyta schlecterii, Xerophyta villosa. Craterostigma wilmsii, Craterostigma plantagineum, Craterostigma pumilum and Eragrostis nindensis. These plants are able to tolerate water stress without undergoing permanent damage. During drying these plants are subjected to different stresses and one such stress is oxidative stress. It has been suggested that polyphenols function as stress protectants in plant cells by scavenging reactive oxygen species (ROS) produced during a period of oxidative stress. In this study the total phenolic content and the related antioxidant capacity of the plants leaf extracts were analysed.
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López, Martínez Gema Isabel. "Functional characterization in vivo of essential Saccharomyces cerevisiae's hydrophilin for desiccation tolerance." Doctoral thesis, Universitat Rovira i Virgili, 2015. http://hdl.handle.net/10803/311618.
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La sobre expressió de les hidrofilines STF2 i SIP18 en soques de laboratori, tenen un efecte positiu en la tolerància a la deshidratació i rehidratació. A més, la sobre expressió de SIP18 en quatre soques comercials de llevat industrial mostra el mateix fenotip que les soques de laboratori sense alterar els paràmetres de la fermentació. Aquests resultats ens permeten proposar la sobre expressió de SIP18 com una possible forma de millorar la viabilitat en el llevat sec actiu (LSA) i obtenir així un inòcul d'alta qualitat per les empreses alimentàries. A més es disminuirien els costos d'emmagatzematge i transport.
La sobre expressió de la hidrofilina SIP18 "preadapta" les cèl·lules incrementant la capacitat de tolerància a la deshidratació i posterior rehidratació degut tan a l'acumulació intracel·lular de SIP18 com als canvis d'expressió proteica que la sobre expressió de SIP18 comporta. Nosaltres hem mostrat l'expressió diferencial de 45 proteïnes que incrementen la seva abundància i 27 que disminueixen durant l'estrès com a conseqüència de la sobre expressió de SIP18. Algunes d'aquestes proteïnes han estat identificades en el procés d'assecat i rehidratació per primera vegada.
Hem identificat altres molècules involucrades en aquest procés d'estrès mitjançant una anàlisi de QTL de dos soques de llevat comercials. Entre els onze gens caracteritzats que van mostrar diferències en la seqüència d'aminoàcids, només la sobre expressió de cinc d'ells mostra un canvi en la viabilitat després de la imposició a l'estrès en els dos contextos genètics analitzats. Aquests resultats mostren que la tolerància a la deshidratació no només depèn de l'activació o inhibició de determinats gens implicats en el procés d'estrès estudiat, sinó també de la seqüència aminoacídica dels al·lels.
Els resultats presentats en aquesta tesi doctoral aprofundeixen en el coneixement dels mecanismes moleculars i els metabòlits involucrats en la tolerància a la deshidratació per a la producció adequada de LSA. No obstant això, també serveix com a model per a futures recerques en l'emmagatzematge de teixits en condicions de deshidratació.La sobre expresión de las hidrofilinas STF2 y SIP18 en cepas de laboratorio, tienen un efecto positivo en la tolerancia a la deshidratación y rehidratación. Además, la sobre expresión de SIP18 en cuatro cepas comerciales de levadura industrial muestra el mismo fenotipo que las cepas de laboratorio sin alterar el proceso fermentativo. Estos resultados nos permiten proponer la sobre expresión de SIP18 como una posible forma de mejorar la viabilidad en la levadura seca activa (LSA) y obtener así un inóculo de alta calidad para las industrías alimentarias. Además se disminuirían los costes de almacenamiento y transporte. La sobre expresión de la hidrofilina SIP18 "preadapta" las células incrementando la capacidad de tolerancia a la deshidratación y posterior rehidratación debido no sólo a la acumulación intracelular de SIP18, sino también a los cambios de expresión proteica que la sobre expresión de SIP18 conlleva. Nosotros hemos mostrado la expresión diferencial de 45 proteínas que incrementan su abundancia y 27 que disminuyen durante el estrés como consecuencia de la sobre expresión de SIP18. Algunas de éstas proteínas han sido identificadas en el proceso de secado y rehidratación por primera vez. Hemos identificado otras moléculas involucradas en este proceso de estrés mediante un análisis de QTL de dos cepas de levadura comerciales. Entre los once genes caracterizados que mostraron diferencias en la secuencia aminopeptídica, sólo la sobre expresión de cinco de ellos muestra un cambio en la viabilidad después de la imposición al estrés en los dos contextos genéticos analizados. Estos resultados muestran que la tolerancia a la deshidratación no sólo depende de la activación o inhibición de determinados genes implicados en el proceso de estrés estudiado, sino también de la secuencia de los alelos. Los resultados presentados en ésta tesis doctoral profundizan en el conocimiento de los mecanismos moleculares y los metabolitos involucrados en la tolerancia a la deshidratación para la producción adecuada de LSA. Sin embargo, también sirve como modelo para futuras investigaciones en el almacenamiento de tejidos en condiciones de deshidratación.
Over expression of STF2 and SIP18 hydrophilin in laboratory has a positive effect on desiccation tolerance. Moreover, over expression of SIP18 in four commercial wine yeast strains produced the same desiccation phenotype as in the laboratory strain without altering fermentative performance. These common results lead us to propose the over expression of SIP18 as a possible way of improving the viability in Active Dried Wine Yeast (ADWY) formulations resulting in savings in transport and storage costs and some extend develope a high-quality inoculum for the food industry. Over-expression of the SIP18 hydrophilin ‘preadapts’ cells by increasing their capacity to overcome and enhance dehydration and rehydration stress. This cell preadaptation is due both to SIP18 accumulation and to changes in the expression of the membrane’s proteomic profile as a consequence of SIP18 accumulation. We shown that 45 proteins increased in numbers after stress imposition and 27 were found to be down regulated, some of which were identified for the first time in this study. Other molecules playin a leading role in enhancing dehydration tolerance were identified using QTL analysis in two commercial wine yeast strains. Characterization of genes with sequence changes between alleles showed that only over expression of five out of eleven genes had different viability for both genetic backgrounds. These results led us to suggest that dehydration tolerance is not gene induced but rather depends on the specific amino acid sequence of each allele in conjunction with other genes activating or inhibiting their function. The results present in this doctoral thesis not only deepen our understanding of the molecular mechanisms and metabolites involved in desiccation tolerance for the production of ADWY, but also serve as a model for future research in tissue storage without the need for a hydric solution.
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Jamell, Sanna. "Differences in desiccation and freezing tolerance in limnic and limno-terrestrial tardigrades." Thesis, Högskolan Kristianstad, Sektionen för lärande och miljö, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hkr:diva-15027.
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Tardigrades are microscopic aquatic invertebrates that are known for their ability to survive extreme conditions. Different species of tardigrades tolerate extreme conditions to a varying degree. It has been suggested that limnic tardigrades would have a lower tolerance to desiccation compared to limno-terrestrial tardigrades. In this study limno-terrestrial species Ramazzottius oberhaeuseri and the limnic species Hypsibius dujardini is compared in regard to their tolerance to desiccation and freezing. The results show that there indeed is a difference in the tolerance and that Ramazzottius oberhaeuseri show better tolerance.
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Vicre, Maїté. "Cell wall involvement in desiccation tolerance in the resurrection plant Craterostigma wilmsii." Doctoral thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/8774.
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Bibliography: leaves 92-129.Resurrection plants have the unique capacity to revive from an air-dried state. In order to cope with desiccation, resurrection plants have to overcome a number of stresses, mechanical stress being one. This occurs when the cytoplasm shrinks creating tension between the plasma membrane and the cell wall. In leaves of the Craterostigma species, an extensive shrinkage occurs during drying as well as a considerable wall folding. It is thought that this folding is a well controlled process rather than a simple collapse and that the ability of the wall to fold is important for the viability of the tissues upon drying. The aim of this study was to characterize the cell wall architecture and composition in hydrated and dry leaves of C. wilmsii using microscopical and biochemical techniques. Calcium and hormone contents were also determined during drying. The development of anhydrous fixation for microscopy confirmed the important folding of the wall previously observed with chemical fixation. Using immunocytochemical techniques and a variety of well characterized antibodies, the nature and composition of wall polymers was investigated. There was nothing unusual in the wall composition of C. wilmsii leaves as compared with other dicotyledonous plants. The results show a significant increase of the hemicellulosic polysaccharide xyloglucan and of the unesterified pectins during drying with levels declining again during rehydration. In contrast no increase was observed in others polysaccharides such as ß (1-4) galactans and methylesterified pectins. Biochemical analysis allowed further characterization of cell wall composition of C. wilmsii. The data demonstrate marked changes in the pectic and hemicellulosic wall fraction from dry plants compared to hydrated ones. The most conspicuous change was a decrease in glucose content in the hemicellulose fraction of the dry plant. Together these findings show that dehydration causes important alteration of polysaccharides content in the cell wall of C. wilmsii. Such modifications might be involved in the modulation of the mechanical properties of the wall during dehydration. Furthermore calcium ions content was shown to increase in the cell wall of dry plants, this could also have a role in stabilizing the wall architecture. All these alterations might be under the control of auxin, an hormone whose content was shown to increase during dehydration.
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Williams, Jason. "Links Between Desiccation Resistance and Cold-Tolerance in an Overwintering Insect: Seasonal and Geographic Trends." Miami University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1124223034.
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Layfield, Johnathon Blake. "Characterization of Hybrid Strains of Saccharomyces pastorianus for Desiccation Tolerance and Fermentation Performance." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-08182009-130032/.
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Dry yeast can be utilized in both ale and lager beer production to provide an inexpensive source of large amounts of viable cells for fermentation. This study examines the desiccation tolerance of different strains of S. pastorianus and the subsequent fermentation performance in comparison to S. cerevisiae. The use of active dry brewerâs yeast (ADY), Saccharomyces cerevisiae, as a starter for the production of ales has been gaining popularity within the brewing industry, spurring manufactures to also produce active dry lager yeast (ADLY), S. pastorianus. The drying process is known to have a greater negative effect on the cell viability and physiology of ADLY than that of ADY, possibly due to the fastidious growth, low production temperature and poor thermotolerance of S. pastorianus. This may result in lower cell viability and concentration of ADLY starter cultures, which could lead to stuck or slow fermentations. S. pastorianus is a hybrid organism resulting from a cross between S. cerevisiae and S. bayanus. It has been proposed that it can be categorized into two distinct groups: Group 1 (S. pastorianus- Saaz type) has lost a significant amount of the genomic content contained within S. cerevisiae and is therefore closer to S. bayanus; while Group 2 (S. pastorianus- Frohberg type) has retained almost all of the genomic content of S. cerevisiae. To investigate whether these two groups differ in their tolerance to desiccation, both groups of S. pastorianus were spray dried at 140oC and rehydrated in phosphate buffer at 25oC for 30 minutes. The viability of the rehydrated cultures was determined using microscopic and viable cell counts. The fermentation performance of the cultures was tested by inoculating equal counts of viable rehydrated cells into brewerâs wort and monitoring changes in cell count, carbohydrate and alcohol concentration until completion. The findings suggest that the S. pastorianus- Frohberg type is less tolerant to desiccation than either S. cerevisiae or S. pastorianus- Saaz type. The Frohberg type shows evidence of membrane damage which could delay the onset of fermentation. Utilization of the correct strain of ADLY could reduce the possibility of contamination or extended lag phases leading to stuck fermentations.
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Lima, Manuel de Jesus Vieira. "Desiccation tolerance, development, maturation and storage of seeds of several tropical tree species." Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297637.
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Koonjul, Priyum K. "Investigating the mechanisms of desiccation tolerance in the resurrection plant, myrothamnus flabellifolius (WELW)." Doctoral thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/9940.
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Biliography : leaves 162-184.Resurrection plants, including Myrothamnus flabellifolius, grow in shallow soil upon rocky outcrops where they experience regular periods of water stress. Associated with this is light stress. The presence of light under water limiting conditions can result in photo-oxidation which causes damage to plant tissues. M flabellifolius is a homoichlorophyllous plant and thus retains chlorophyll during desiccation. The mechanisms whereby this plant prevents photo-oxidation damage are not known and thus one of the objectives of this study was to characterise the chloroplasts and the changes they undergo during dehydration. It was shown that chloroplasts from M flabellifolius could only be isolated using trehalose gradients (instead of sucrose gradients) and were found to have a higher buoyant density than chloroplasts isolated from another resurrection plant, Craterostigma wilmsii. The latter had the same buoyant density as those isolated from the desiccation sensitive plant Pisum sativum. The increased buoyant density in M flabellifolius was ascribed to the unusual ultrastructure of the thylakoid membranes. The latter have a staggered conformation (staircase arrangement) rather than the discrete granal and intergranal conformation found in most plants.
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Kruger, Lynette Anne. "Towards an understanding of the mechanisms of desiccation tolerance in Myrothamnus flabellifolius (WELW.)." Master's thesis, University of Cape Town, 1998. http://hdl.handle.net/11427/17369.
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Bibliography: pages 110-123.To date, most of the studies on the homoiochlorophyllous desiccation-tolerant (HDT) plant Myrothamnus flabellifolius have been conducted on excised twigs or leaves. In this study drying (including prolonged exposure to the dry state), and recovery of whole plants was compared with that of detached twigs dried off the plant, and also with twigs excised after having dried on the plant. Study of the leaf response during drying and recovery in the presence and/or absence of roots, and following prolonged desiccation, can contribute towards understanding the mechanisms of desiccation tolerance in M. flabellifolius.
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Koshawatana, Chutima. "Physiological, biochemical and chemical studies on desiccation tolerance primarily in developing wheat seeds." Title page, contents and summary only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phk859.pdf.
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Bibliography: leaves 155-182. Most agricultural crop seeds are 'orthodox' ie. desiccation is a necessary feature of their complete life cycle. Low moisture content lengthens the storage life of orthodox seeds. Recalcitrant seeds, which do not tolerate low moisture content, lose viability in dry storage. The thesis studies the role of sugars in desiccation tolerance in developing seeds and investigates other mechanisms which might be involved in desiccation tolerance and desiccation sensitivity.
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Ferebee, James Harrison IV. "New Herbicide Strategies for Weed Management in Pumpkin and Soybean and Potato Vine Desiccation." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/86611.
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Weed control and desiccation are routinely executed with herbicides. Potato vine desiccation facilitates harvest, improves skin set, and regulates tuber size. Saflufenacil, glufosinate, saflufenacil plus glufosinate, and carfentrazone plus glufosinate were compared to diquat applied at 43, 31, and 17% B potatoes; similar vine desiccation (14 days after treatment), skin set, and yield were noted amongst treatments. Residual herbicides are routinely used for weed control in pumpkin. Fluridone and acetochlor formulations applied preemergence were evaluated in direct-seeded pumpkin compared to other labeled herbicides. Fluridone resulted in total crop loss following heavy rainfall immediately after planting; less rainfall resulted in transient injury. Acetochlor formulations resulted in significant pumpkin injury (34 to 39%) 14 days after planting. S-metolachlor controlled weeds similar to acetochlor without significant injury. Palmer amaranth has developed resistance to six different herbicide modes of action. The weed grows rapidly and is best controlled <10 cm in height. To control glyphosate and ALS- resistant biotypes, fomesafen plus dicamba were applied at first postemergence (POST) to small Palmer amaranth (<5 cm, 0 d) and at simulated delays of 7, 14, 21, and 28 d. All plots received lactofen plus dicamba 14 days after first POST. Palmer amaranth control 14 days after first POST was 100% when delayed 0 or 7 d and 62% at the 28 day delay; control increased to 88% following lactofen plus dicamba applied second POST. Yield was significantly reduced when first POST was delayed 28 days at one location.Master of Science in Life Sciences
Herbicides effectively control weeds by either applying them to the soil prior to emergence or applying them to foliage. Herbicides are used for desiccation of potato vines to facilitate harvest, improve skin set, and regulate tuber size. Potatoes with tougher skin have a longer shelf life and are more resistant to disease. Potato grade classifications include size chef, A, and B potatoes. Size B potatoes hold the greatest value for redskinned potatoes. Experiments were conducted in Virginia to evaluate saflufenacil, glufosinate, saflufenacil plus glufosinate, and carfentrazone plus glufosinate as desiccants compared to diquat applied at 43, 31, and 17% B potatoes. All desiccants resulted in similar vine desiccation 14 days after treatment, skin set, and yield. This research demonstrates that glufosinate and saflufenacil are effective alternatives to diquat for potato vine desiccation; however, further research is needed to evaluate the safety of saflufenacil applied to potatoes prior to harvest. Soil applied herbicides are commonly used in pumpkin production. Fluridone and two acetochlor formulations, herbicides that effectively control troublesome weeds in other crops, were evaluated for pumpkin production in addition to fomesafen, ethalfluralin, clomazone, halosulfuron, and S-metolachlor. Fluridone and acetochlor formulations resulted in significant pumpkin injury early in the growing season and total crop loss was observed by fluridone in 2018. Fomesafen significantly reduced pumpkin iv stand and yield. S-metolachlor, a member of the same chemical family as acetochlor, provided similar weed control without significant pumpkin injury. This research demonstrates that fluridone and acetochlor formulations are poor candidates for pumpkin production. Palmer amaranth is a troublesome weed in soybean that grows rapidly and is resistant to many herbicides. Palmer amaranth is best controlled at a height of 10 cm or less, but timely applications are not always feasible. Fomesafen plus dicamba were applied to small Palmer amaranth (<5 cm, 0 day) and at simulated delays of 7, 14, 21, and 28 days. All treatments received lactofen plus dicamba 14 days after the initial postemergence. Palmer amaranth control 14 days after first postemergence was 100% when application was delayed 0 or 7 day whereas Palmer amaranth control was 62% when first postemergence was delayed 28 days. Lactofen plus dicamba applied second postemergence increased control to 88% when the first postemergence was delayed 28 days. Compared to nontreated plots, Palmer amaranth biomass was reduced 99% by all treatments. This research demonstrates that fomesafen plus dicamba followed by lacofen plus dicamba can be effective for rescue control of Palmer amaranth.
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Silva, João Paulo Naldi [UNESP]. "Mecanismos de controle de tolerância à dissecação em sementes de Caesalpinia echinata LAM. (Pau-Brasil) e Caesalpinia peltophoroides BENTH. (Sibipiruna)." Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/92096.
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A aquisição da tolerância à dessecação ocorre durante a maturação da semente, após acúmulo de reservas e antes do início do processo natural de secagem, porém, com o avanço da germinação a sensibilidade a dessecação aumenta. Estresses hídricos podem induzir ou restabelecer a tolerância à dessecação em sementes, porém, não se sabe em quais processos ele atua, como na ativação de genes. O objetivo deste trabalho foi avaliar a aquisição e perda de tolerância à dessecação em sementes de Caesalpinia echinata Lam. (pau-brasil), e a possibilidade de indução deste processo avaliando as modificações nos carboidratos solúveis e de ciclitóis, nos níveis endógenos de ABA e na expressão de aquaporinas. Foram observadas diferenças na aquisição de tolerância em sementes imaturas de mesma idade, produzidas nas mesmas matrizes em 2007 e 2008, com diferentes composições de carboidratos solúveis. Sementes maduras perdem a tolerância à dessecação logo após protrusão da raiz primária, em comprimentos dependentes do grau de deterioração da semente. Sementes imaturas e maduras tolerantes de C. echinata suportaram a desidratação de formas diferentes, utilizando reservas de amido e ciclitóis, com papel da sacarose quando secas. Esses resultados foram comparados com sementes de Caesalpinia peltophoroides Benth (sibipiruna), demonstrando comportamentos fisiológicos distintos, provavelmente relacionados com o tipo de reserva que acumulam
The acquisition of desiccation tolerance occurs during seed maturation, after reserves accumulation and before the natural process of drying, however, with seed germination the desiccation sensitivity increases. Water stress can induce or restore the desiccation tolerance in seeds, but it is unclear what processes it acts, like activation of genes. The objective of this work was to evaluate the acquisition and loss of desiccation tolerance in Caesalpinia echinata Lam (brazil-wood) seeds, and the possibility to induction this process, evaluating the soluble carbohydrates and cyclitols changes, the ABA endogenous levels and expression of aquaporins. Differences were observed in the tolerance acquisition in immature seeds of the same age, produced by the same trees in 2007 and 2008, showing different compositions of soluble carbohydrates. Mature seeds lose desiccation tolerance soon after radicle protrusion in length depending on the degree of seed deterioration lot. Immature and mature tolerant seeds of C. echinata support the dehydration by different ways, using starch reserves and cyclitols, seen sucrose when the seed dry. These results were compared with seeds of Caesalpinia peltophoroides (sibipiruna), showing different physiological parameters, probably related to the type of reserves that they accumulate
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Otieno, Mary Atieno. "Proteomic Changes in Rhizobia after Growth in Peat Extract and Their Potential Role in Desiccation Tolerance." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17791.
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Survival of rhizobia on seed is mainly affected by desiccation. Inherent differences in survival exist between rhizobia strains as well as with growth conditions, with a general improvement in survival seen in cells grown in peat over cells grown on growth media. Improving survival of rhizobia under desiccation stress may enhance nitrogen fixation and crop yields. This study aimed to relate desiccation tolerance of rhizobia to physiological changes in cells grown in peat extract. Survival of four rhizobia strains (Rhizobium leguminosarum bv. viciae, 3841, Rhizobium leguminosarum bv. trifolli TA1, Bradyrhizobium japonicum, CB1809, Bradyrhizobium diazoefficiens sp. nov.) was measured after growth in peat extract. This study reported an improvement in survival of Bradyrhizobium strains USDA110 and CB1809 compared to the Rhizobium strains 3841 and TA1. The global proteomic responses of the four rhizobia strains after growth in peat extract was compared with defined medium JMM. Differentially expressed proteins were reported across the four strains with a possible role in desiccation tolerance such as ABC transporters, stress response, transcription, translation and oxidative stress proteins. The role of one protein, PspA (RL3579), was validated by creating a knock-out mutant. The RL3579 mutant grown in peat extract reported significantly lower percentage survival of 2% as compared to the wild-type (5.3%), and could be attributed to loss in membrane integrity. This study confirms that survival of rhizobia can be improved after growth in peat extract, due to stress-related proteins that may function in protecting cells from desiccation-induced damage. The roles of these stress proteins and effect of specific components of peat could be manipulated to develop desiccation-tolerant strains and inform development of new inoculant carriers for legume inoculation.
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Hill, Donna René. "Morphological, biochemical and molecular characterization of desiccation-tolerance in cyanobacterium Nostoc commune var. Vauch." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40154.
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Filaments of the desiccation-tolerant cyanobacterium Nostoc commune are embedded within, and distributed throughout, a dense glycan sheath. Analysis of the glycan of field materials and of pure cultures of N. commune DRH1 through light and electron microscopy, immunogold-labelling and staining with dyes, revealed changes in the pattern of differentiation in glycan micro-structure, as well as localized shifts in pH, upon rehydration of desiccated field material. A Ca/Si rich external (pellicular) layer of the glycan acts as a physical barrier on the surface of N. commune colonies. A purified fraction (> 12 kDa) of an aqueous extract of the glycan from desiccated field material contained glucose, N -acetylglucosamine, glucosamine, mannose and galactosamine with ratios of 3.1 : 1.4 : 1 : 0.1 : 0.06, respectively. Ethanol extracts of N. commune contained trehalose and sucrose and the levels of both became undetectable following cell rehydration. Elemental analysis of glycan extracts showed a flux in the concentrations of salts in the glycan matrix following rehydration of desiccated colonies. Intracellular cyanobacterial trehalase was identified using immunoblotting and its synthesis was detected upon rehydration of desiccated field cultures. Water-stress proteins (Wsp; molecular masses of 33, 37, and 39 kDa are the most abundant proteins in glycan), a water soluble UV-AlB-absorbing pigment, the lipid-soluble UV-protective pigment scytonernim, as well as two unidentified cyanobacterial glycoproteins (75 kDa and 110 kDa), were found within the glycan matrix. No evidence was found for either glycosylation, phosphorylation or acylation of Wsp polypeptides. NH2-terminal sequence analysis of the three proteins of Wsp were identical: Ala-Leu-Tyr-Gly-Tyr-Thr-Ile-Gly-Glu-Gln-X-Ile-Gln- Asn-Pro-Ser-Asn-Pro-Ser-Asn-Gly-Lys-Gln. An unidentified 68-kDa protein, the second most abundant protein in aqueous extracts of the glycan, was isolated and its N-terminal sequenced was determined: Ala-Phe-lle-Phe-Gly-Thr-Ile-Ser-Pro-Asn-Asn-Leu-Ser-Gly- Thr-Ser-Gly-Asn-Ser-Gly-Ile-Val-Gly-Ser-Ala. Gene bank searches with these sequences, and an internal sequence ofWsp (Glu-Ala-Arg-Val-Thr-Gly-Pro-Thr-Thr-Pro-Ile-Asp), identified homologies with various carbohydrate-modifying enzymes. Purified Wsp polypeptides associate with 1,4-β-D-xylanxylanohydrolase activity that was inhibited specifically by Wsp antiserum. In the absence of salt, Wsp polypeptides, and the water-soluble UV -A/B-absorbing pigments, form multimeric complexes through strong ionic interactions. The role of the glycan, and the protein and pigments that reside within it, in the desiccation tolerance of N. commune is discussed with respect to structure/function relationships.Ph. D.
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Philip, Benjamin N. "Characterization and physiological role of aquaporins during desiccation and freezing in Eurosta solidaginis." Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1280843234.
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Wiswedel, Stefan. "Mohria caffrorum (L.) Desv. : a new, unique model organism for the study of desiccation tolerance." Bachelor's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/23926.
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Vegetative desiccation tolerance is the ability of a plant to dry to equilibrium with its surrounding atmosphere and remain in this dry state for prolonged periods of time. Upon rehydration, these plants are able to regain full physiological functionality. Vegetative desiccation tolerance is common and partially understood in the less complex clades including the algae, bryophytes and lichens but is uncommon in the vascular land plants. Vegetative desiccation tolerance is partially understood in the angiosperms but there has been little work on desiccation tolerance in pteridophytes Mohria caffrorum (L.) Desv is one such desiccation tolerant pteridophyte This fern has the unique characteristic of having both desiccation tolerant and desiccation sensitive forms, which alternate seasonally, which this study is the first to show. We show here that; 1) M caffrorum is indeed a desiccation tolerant fern. 2) M. caffrorum has desiccation tolerant and desiccation sensitive frond types. which are morphologically distinct. 3) These morphological differences are directly related to the ability to survive desiccation as well as playing a role in tine ecologies of the two growth forms. 4) The spores of M. caffrorum are also desiccation tolerant. A hypothesis is proposed detailing why M. caffrorum is able to change between being desiccation tolerant and desiccation sensitive.
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Milborrow, Evan. "Non-coding RNA networks regulating leaf vegetative desiccation tolerance in the resurrection plant Xerophyta humilis." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29437.
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Common to orthodox seeds, desiccation tolerance (DT) is exceedingly rare in the vegetative tissues of modern angiosperms, being limited to a small number of "resurrection plants". While the molecular mechanisms of DT, as well as the transcription factors regulating the seed and vegetative DT programmes, have been identified, very little is known with regards to the role of regulatory noncoding RNAs (ncRNAs). To investigate the presence and roles of possible ncRNA players, RNA-Seq was performed on desiccating Xerophyta humilis leaves and a bioinformatic pipeline assembled to identify the potential decoy lncRNAs and miRNAs present. Interaction mapping was performed, identifying a number of small regulatory networks each regulating a small subset of the desiccation transcriptome. Predicted networks were screened for function related to DT and expression consistent with functional regulatory interactions. Of the predicted networks, two appear highly promising as potential regulators of key DT response genes. The results indicate that differentially expressed (DE) desiccation response ncRNAs are present in the vegetative tissues of X. humilis and likely play a key role in the regulation of DT. This suggests that ncRNAs appear to play a more important role in DT than previously thought, and may have facilitated the evolution of vegetative DT through reprogramming of seed DT programs in vegetative tissues.
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Peng, Congyue. "Characterization of a membrane protein encoding cDNA (TrDr3) from the desiccation-tolerant moss Tortula ruralis /." Available to subscribers only, 2008. http://proquest.umi.com/pqdweb?did=1597629781&sid=2&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Silva, Joao Paulo Naldi. "Mecanismos de controle de tolerância à dissecação em sementes de Caesalpinia echinata LAM. (Pau-Brasil) e Caesalpinia peltophoroides BENTH. (Sibipiruna) /." Botucatu : [s.n.], 2010. http://hdl.handle.net/11449/92096.
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Orientador: Claudio José BarbedoBanca: Jose Maria Rocha Faria
Banca: João Rodrigues Domingos
Resumo: A aquisição da tolerância à dessecação ocorre durante a maturação da semente, após acúmulo de reservas e antes do início do processo natural de secagem, porém, com o avanço da germinação a sensibilidade a dessecação aumenta. Estresses hídricos podem induzir ou restabelecer a tolerância à dessecação em sementes, porém, não se sabe em quais processos ele atua, como na ativação de genes. O objetivo deste trabalho foi avaliar a aquisição e perda de tolerância à dessecação em sementes de Caesalpinia echinata Lam. (pau-brasil), e a possibilidade de indução deste processo avaliando as modificações nos carboidratos solúveis e de ciclitóis, nos níveis endógenos de ABA e na expressão de aquaporinas. Foram observadas diferenças na aquisição de tolerância em sementes imaturas de mesma idade, produzidas nas mesmas matrizes em 2007 e 2008, com diferentes composições de carboidratos solúveis. Sementes maduras perdem a tolerância à dessecação logo após protrusão da raiz primária, em comprimentos dependentes do grau de deterioração da semente. Sementes imaturas e maduras tolerantes de C. echinata suportaram a desidratação de formas diferentes, utilizando reservas de amido e ciclitóis, com papel da sacarose quando secas. Esses resultados foram comparados com sementes de Caesalpinia peltophoroides Benth (sibipiruna), demonstrando comportamentos fisiológicos distintos, provavelmente relacionados com o tipo de reserva que acumulam
Abstract: The acquisition of desiccation tolerance occurs during seed maturation, after reserves accumulation and before the natural process of drying, however, with seed germination the desiccation sensitivity increases. Water stress can induce or restore the desiccation tolerance in seeds, but it is unclear what processes it acts, like activation of genes. The objective of this work was to evaluate the acquisition and loss of desiccation tolerance in Caesalpinia echinata Lam (brazil-wood) seeds, and the possibility to induction this process, evaluating the soluble carbohydrates and cyclitols changes, the ABA endogenous levels and expression of aquaporins. Differences were observed in the tolerance acquisition in immature seeds of the same age, produced by the same trees in 2007 and 2008, showing different compositions of soluble carbohydrates. Mature seeds lose desiccation tolerance soon after radicle protrusion in length depending on the degree of seed deterioration lot. Immature and mature tolerant seeds of C. echinata support the dehydration by different ways, using starch reserves and cyclitols, seen sucrose when the seed dry. These results were compared with seeds of Caesalpinia peltophoroides (sibipiruna), showing different physiological parameters, probably related to the type of reserves that they accumulate
Mestre
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Shoko, Ryman. "A proteomic investigation of the rhizomes of the resurrection fern Mohria caffrorum L. (Desv.) in response to desiccation." Doctoral thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/16779.
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Includes bibliographical referencesAs there is limited information on the mechanisms of vegetative desiccation-tolerance in resurrection plant rhizomes, this work was undertaken to study the mechanisms of desiccation-tolerance in Mohria caffrorum rhizomes. Fronds of this plant have been previously characterized as being desiccation-tolerant in summer and desiccation-sensitive in winter. Since fern rhizomes are perennial organs, it was of interest to establish whether these organs are also perennially desiccation-tolerant and, whether or not the rhizomes regulate desiccation-tolerance in the fronds. Ultra-structural evidence using transmission electron microscopy and viability studies using electrolyte leakage analysis showed that the rhizomes were desiccation-tolerant throughout the seasons. Quantitative proteomics analysis using isobaric tags for relative and absolute quantification was employed to investigate molecular mechanisms of desiccation-tolerance in the rhizomes of this plant. Using a custom fern rhizome specific peptide sequence database, 236 proteins were identified. Of these, 16 proteins increased in abundance while 14 declined, in the summer collected rhizomes. On the other hand, 16 proteins increased in abundance and 20 declined in the winter form. Western blot analysis confirmed the expression trends of heat shock protein 70-2 and superoxide dismutase-[Cu-Zn], which were among the differentially expressed proteins. Bioinformatics analysis of the differentially expressed proteins was carried out using network enrichment tools, to identify key molecular processes and pathways involved in the rhizome response to desiccation stress. Results indicate that the rhizomes use different molecular mechanisms to achieve desiccation-tolerance in winter and summer. Potential cross-talks and cross-tolerances were identified in which mechanisms protecting the rhizomes against desiccation-tolerance appeared to also protect them against heat stress, and in winter an apparent cross-talk against desiccation and pathogen stresses was also identified. This study is the first report of evidence that M.caffrorum rhizomes are the 'master-regulator organs' responsible for regulating desiccation-tolerance in the fronds. This role was inferred from the rhizome's predicted up-/down-regulation of biological processes and pathways that relate to leaf senescence, shoot system morphogenesis and gametophyte development, among others.
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Sines, Brian James. "Isolation and partial characterization of a water stress protein of the desiccation-tolerant cyanobacterium Nostoc commune UTEX 584 expressed in Escherichia coli." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/46434.
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A desiccation-tolerant cyanobacterium Nostoc commune accumulates a novel group of water stress proteins (Wsp) in response to cycles of repeated drying and rehydration. Antibodies, specific for Wsp, were used to screen a lambdafix II library of N. commune UTEX 584 Bam H1 DNA fragments and an 8.5-kb fragment, containing a gene cluster that synthesized a 59-kDa cross-reactive protein. The cloned fragment comprised five ORF’s. The ORF’s 59, 24, 22, 36, and 70, each potentially encode products of molecular weights of 59, 24, 22, 36, and 70-kDa, respectively. The 59 and 24 ORF products were found to be expressed in E. coli. The 59-kDa product of this fragment gives the strongest cross-reaction with the Wsp antiserum. The 59-kDa protein was partially purified. The 24-kDa product was successfully purified to homogeneity and partially characterized.
This study used E. coli strain DH10B transformed with the pTrc 99A plasmid. The pTre 99A contains the 8.5-kb gene cluster fragment of interest. The products of ORF 24 and 59 were isolated using an initial 40-60 % ammonium sulfate precipitation of a clarified E. coli cell lysate. The clarified cell lysate was then subjected to streptomycin sulfate precipitation. The cell lysate was then dialyzed extensively. The cell lysate was then applied to a Mono Q HR 5/5 anion exchange column using a 2 M KCl gradient elution procedure. The Mono Q column yielded a fraction containing both ORF products which eluted with approximately 400 mM KCl. This fraction was then applied to a Superose 12 HR 10/30 gel filtration column. The eluent fraction containing the ORF 24 product was then reapplied to the Superose 12 to yield the final fraction containing only the ORF 24 product. The final fraction of ORF 24 was purified to homogeneity as determined by SDS-PAGE analysis. Approximately 750 μg of ORF 24 was isolated. This preparation was used for characterization studies.
Characterization studies of ORF 24 consisted of an amino-terminal sequence analysis, an estimation of the molecular weight using gel filtration chromatography and SDS-PAGE analysis, and an analysis of enzymatic activity as suggested by amino acid sequence homologies. The amino-terminal sequence of ORF 24 is P V E Q R S H D. The molecular weight of ORF 24 using gel-filtration chromatography and SDS-PAGE analysis is 26-kDa and 23-kDa, respectively. From gene sequence analysis, the molecular weight of ORF 24 is known to be 24,340-Da. These data indicate that ORF 24 is a monomer. ORF 24 was found to have amino acid sequence homologies with a pectate lyase (E 4.2.2.2) periplasmic precursor from Erwinia caratovora subspecies and a dextransucrase (EC 2.4.1.5) precursor from Streptoccocus mutans GS-5. However, pectate lyase activity was not detected in cellular extracts over a 24 hour period. In addition, ORF 24 was not found to interact with 10 % substrate solutions of N-acetylglucosamine, pectin, UTEX 584 sheath material, DRH1 sheath material, sucrose, or glucose using thin layer chromatography. These studies indicate that the enzymatic activities proposed from amino acid sequence homologies have not been detected. The suggestion that ORF 24 is a water stress protein with a protective function on a structural level with regards to desiccation-tolerance requires further study.Master of Science
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Svensson, Jan. "Functional studies of the role of plant dehydrins in tolerance to salinity, desiccation and low temperature /." Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 2001. http://epsilon.slu.se/avh/2001/91-576-5779-3.pdf.
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Walford, Sally-Ann. "Activation of seed-specific genes in leaves and roots of the desiccation tolerant plant, Xerophyta humilis." Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/4349.
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Includes abstract.Includes bibliographical references (leaves 131-169).
The ability of tissues to survive almost complete loss of cellular water is a trait found throughout the plant kingdom. While this desiccation tolerance is common in seeds of most angiosperms it is rare in their vegetative tissues. Xerophyta humilis (Bak.) Dur and Schintz belongs to a small group of resurrection angiosperms and it possesses the ability to withstand extreme desiccation of greater than 90% in both its seeds and vegetative tissues and return to active metabolism upon rehydration. We have tested the hypothesis that vegetative desiccation tolerance in angiosperms has evolved as an adaptation of seed desiccation tolerance.
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Ludanyi, Monika. "Extreme radiation tolerance of Deinococcus deserti : Characterization of the central regulator IrrE." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4066.
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Les bactéries du genre Deinococcus sont extrêmement tolérantes à de fortes doses de radiations. Des études antérieures ont montré que IrrE est nécessaire à la radiotolérance et à l'induction des gènes de réparation de l'ADN après exposition des cellules à l'irradiation. Pendant des années il est resté inconnu comment IrrE active l'expression de ces gènes. L'objectif de ma thèse était la caractérisation de la voie de signalisation dépendent de IrrE chez Deinococcus deserti. Pour cela, des approches biochimiques et génétiques ont été utilisées. Les premiers résultats ont fortement suggéré que IrrE agit indirectement sur l'activation de l'expression des gènes. En utilisant des expériences in vitro et in vivo, nous avons montré que IrrE de Deinococcus deserti interagit avec DdrO, un régulateur potentiel qui est codé par un gène radio-induit et qui est, comme IrrE, conservé chez les Deinococcus. De plus, IrrE clive DdrO in vitro mais aussi in vivo lorsque les deux protéines sont co-exprimées chez Escherichia coli. Ce clivage est abolit en présence d'un agent chélateur de métaux, l'EDTA. Chez D. deserti, le clivage de DdrO dépendent de IrrE a été observé mais seulement après exposition à l'irradiation. En parallèle, nous avons montré que la répression du promoteur d'un gène radio-inductible est dépendante de DdrO. Nos résultats montrent donc que IrrE est une métalloprotéase et nous proposons que le répresseur DdrO soit désactivé après clivage par IrrE conduisant à l'induction de différents gènes indispensables pour la réparation de l'ADN et la survie des cellules après exposition de Deinococcus à l'irradiationDeinococcus bacteria are famous for their extreme tolerance to high doses of radiation. Earlier studies have shown that IrrE protein is required for radiation tolerance and for induction of DNA repair genes after exposure of cells to radiation. However, for years it has remained unknown how IrrE activates gene expression. The aim of my thesis was to characterize the IrrE-dependent regulation pathway in Deinococcus deserti. For this, biochemical and genetic approaches were used. The first results strongly suggested that IrrE activates gene expression in an indirect manner. Then, using other in vivo and in vitro experiments, IrrE from Deinococcus deserti was found to interact with DdrO, a predicted regulator encoded by a radiation-induced gene that is, like irrE, highly conserved in Deinococcus. Moreover, IrrE was found to cleave DdrO in vitro and also in vivo when the proteins were co-expressed in Escherichia coli. This cleavage was not observed in the presence of the metal chelator EDTA. In D. deserti, IrrE-dependent cleavage of DdrO was observed only after exposure to radiation. Furthermore, DdrO-dependent repression of the promoter of a radiation-induced gene was shown. Our results demonstrate that IrrE is a metalloprotease and we propose that IrrE-mediated cleavage inactivates repressor protein DdrO, leading to transcriptional induction of various genes required for DNA repair and cell survival after exposure of Deinococcus to radiation
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Smith-Espinoza, Claudia J. "Analysis of ABA and drought stress mediated gene expression in the desiccation tolerant resurrection plant Craterostigma plantagineum." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963130862.
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Smith, Michaela Madeleine 1972. "Maintenance of ultrastructural integrity during dehydration in a desiccation tolerant angiosperm as revealed by improved preservation techniques." Monash University, Dept. of Biological Sciences, 2002. http://arrow.monash.edu.au/hdl/1959.1/8323.
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Dimson, Emily V. "Development and desiccation tolerance of the seeds of Acer rubrum L., Acer saccharinum L. and their hybrid." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ40408.pdf.
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Gasulla, Vidal Francisco. "Insights on desiccation tolerance of the lichen photobiont trebouxia sp. pl. in both thalline and isolated ones." Doctoral thesis, Universitat de València, 2009. http://hdl.handle.net/10803/39081.
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The study of desiccation tolerance of lichens, and of their phycobionts in particular, has been mainly focused on the antioxidant system that protects the cell against photo-oxidative stress produced during dehydration and rehydration. However, desiccation tolerance cannot be achieved in lichen phycobionts with antioxidant activity alone. The main objective of the thesis was to expand the knowledge of the poorly understood desiccation tolerant mechanisms.
The first chapter presents an introduction to the subject of the thesis, based on the available background information, and explains the rationale of the thesis.
The aim of the chapter 2 was to establish the optimal growing conditions for the isolated phycobiont Trebouxia erici Ahmadjian (SAG 32.85 = UTEX 911) and to determine how these working procedures could modify the results of further experiments. We concluded that cellulose-acetate discs for agar cultures should be inoculated with 14-day-old liquid cultures, and growth under irradiance of 30 mol m-2 s-1 PAR at 20 ºC. Experiments should be carried out with 21day-old algal discs.
The experiments carried out in third chapter were designed on one hand, to determine the grade of desiccation tolerance of the isolated lichen phycobiont T. erici, and on the other hand, we studied the response of some protective mechanisms. The results showed that both long desiccations and rapid drying produced greater membrane damage and lower recovery of metabolic and photosynthetic activity than after brief desiccations and slow drying, respectively. Photosynthesis was never recovered totally neither after rapid nor slow drying. Classical mechanisms involved in the protection of the cell against oxidative stress were present in hydrated algae although were not enhanced during dehydration/rehydration. Likewise, in T. erici, dehydrins were also constitutively expressed. However, a slow drying time was required for activating the conformational change in the photosystem II which protect against photoinhibition in desiccation state.
In the fourth chapter we decided to carry out proteomic and genetic expression analyses of the changes associated with desiccation and rehydration in the isolated phycobiont Trebouxia erici, in order to find out other proteins that may be involved on desiccation tolerance mechanisms of phycobionts. Proteomic analysis showed that desiccation caused up-regulation of around 19 proteins and down-regulation of 43 proteins. Among the proteins up-regulated during drying were found: a putative cation transport protein; a protein with an F-box domain; a cell division cycle 48 protein; -tubulin protein; a 90 kDa Heat shock protein. We observed that five Hsp90 and two -tubulin genes were activated during dehydration and mRNA was accumulated until the cell was completely dried.
In the fifth chapter we investigated the role of the NO in the biochemical interaction between lichen symbionts and whether the NO may increase the endurance of lichenized phycobionts under desiccation. Rehydration of the lichen R. farinacea caused the release of NO together with a high production of ROS. The amount of NO detected decreased significantly with the addition of c-PTIO. In the isolated phycobionts, scavenging of the self produced NO caused a decrease in the recovery of photosynthetic activity after dehydration, probably due to the higher levels of photo-oxidative stress.
The aim of the work presented in the sixth chapter was to determine the effect of cell ageing in desiccation resistance of T. erici. Phycobiont capacity to recover photosynthesis activity after desiccation was inversely related with cell ageing, suggesting that desiccation tolerance is age-dependent.
The results presented in this thesis demonstrate that desiccation tolerance of T. erici is achieved by a complex system of constitutive and induced mechanisms. Moreover, some factors such as drying rate, desiccation duration, lichenization and ageing may alter the recovery capacity of T. erici after desiccation.El estudio de la tolerancia a la desecación de los líquenes, y de sus fotobiontes en particular, ha sido principalmente enfocado hacia los sistemas antioxidantes que protegen a la célula frente al estrés fotoxidativo. Sin embargo, la tolerancia a la desecación no puede ser alcanzada solamente con sistemas antioxidantes. Por esta razón, el objetivo principal de esta tesis fue profundizar en el conocimiento de los mecanismos de tolerancia a la desecación en fotobiontes liquénicos. El fotobionte liquénico Trebouxia erici Ahmadjian mostró ser tolerante a la desecación incluso cuando es cultivado separado de su compañero micobionte. Sin embargo, la resistencia a la desecación dependió de la velocidad de deshidratación, del tiempo de desecación y del envejecimiento del cultivo. Tasas de deshidratación altas, largos periodos de desecación y cultivos viejos redujeron la capacidad de recuperación. Esto es debido a que la tolerancia a la desecación del fotobionte se consigue por un lado mediante mecanismos de protección celular que son constitutivamente expresados como, enzimas antioxidantes, xantofilas o proteínas LEA, junto con la activación Mientras que por otro, existen mecanismos que se activan durante la deshidratación, como son de la síntesis de proteínas implicadas en el transporte, la protección de membranas y proteínas, el citoesqueleto, el ciclo celular y el marcaje y la degradación de proteínas. Aunque los fotobiontes liquénicas tienen sus propios mecanismos para resistir la desecación, en la relación simbióntica la tolerancia a la desecación podría ser aumentada por otros mecanismos. Nuestros estudios con el liquen Ramalina farinacea Ach. y fotobiontes aislados mostraron que el gas bioactivo oxido de nitrógeno (NO) es liberado principalmente por el hongo durante la rehidratación del talo, el cual podría tener un papel importante en la maquinaria antioxidante del fotobionte durante las primeras fases de la rehidratación.
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Joardar, Vinita. "Molecular analysis of genes involved in carbohydrate metabolism in the desiccation-tolerant cyanobacterium Nostoc commune UTEX 584." Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/40311.
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Synthesis of water stress proteins (Wsp) is induced upon repeated desiccation and rehydration of immobilized cells of the desiccation-tolerant cyanobacterium Nostoc commune UTEX 584 (Nostoc 584). The Wsp polypeptides synthesized and secreted by field material of N. commune have been extensively characterized and shown to exist as three isoforms with molecular masses of 33, 37 and 39 kDa. In order to understand the role of Wsp in the mechanism of tolerance to water stress an attempt was made to isolate the gene(s) that encodes Wsp in Nostoc 584. A polyclonal antibody raised against a mixture of the isoforms was used to screen expression libraries (phage and plasmid) of Nostoc 584 genomic DNA fragments. This work presents the analysis of clones, isolated from the expression libraries, which cross react with Wsp antiserum. Sequencing of the DNA from one of the cross reacting clones revealed an incomplete open reading frame (ORFA) that showed strong similarity to two fructose bisphosphate aldolases, CfxA and CfxB, from the photosynthetic purple non-sulfur bacterium, Rhodobacter sphaeroides. A promoter region present upstream of ORFA is recognized by RNA polymerase from E. coli. Further upstream of the promoter lies trnK encoding lysyl-tRNA, identified by evident similarity to the corresponding gene from the chloroplast of the liverwort, Marchantia polymorpha. The remainder of the aldolase gene (fba) was isolated using the colony hybridization technique. Sequence analysis of DNA from the second cross reactive clone revealed six ORFs (ORFs 1 through 6).The products of ORFI and ORF2 are overproduced in this clone. The polypeptide encoded by ORFI shows very strong cross-reactivity with the polyclonal Wsp antibody, whereas ORF2 does not. Database searches using the deduced amino acid sequences of the six ORFs have provided clues to the possible identities of these ORFs. ORF6 shows correspondence with a protein, in Arabidopsis thaliana, which is induced in response to cold, abscissic acid and water stress. The common feature shared by ORFs 1 to 5 is that the highest similarities are observed with enzymes involved in carbohydrate metabolism. ORFs 1 through 5 may possibly represent a novel cluster of genes that form all or part of an operon involved in the metabolism of carbohydrates in Nostoc 584. Fructose bisphosphate aldolase (EC 4.1.2.13) is a key enzyme in carbohydrate metabolism, playing a role in glycolysis as well in the Calvin cycle of carbon dioxide fixation. The potential roles played by aldolase and the products of ORFs 1 through 5 in overall carbon metabolism of Nostoc commune UTEX 584 are discussed.Ph. D.
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Brown, Carly. "A comparison of some potential indicators of desiccation-tolerance in 2 Poikilochlorophyllous Xerophyta species and Homiochlorophyllous Craterostigma wilmsii." Bachelor's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/24762.
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Three possible indicators of desiccation-tolerance in ang10sperms: sucrose accumulation and hexose sugar flux, an increase in hexokinase activity, and accumulation of LEA-like proteins, were investigated and compared during dehydration between two moncotyledonous poikilochlorophyllous resurrection angiosperm species; Xerophyta schlecterii and Xerophyta humilis, and a dicotyledonous homiochlorophyllous resurrection species, Craterostigma wilmsii. Comparisons were also made with Xerophyta viscosa, using data from Whittaker et al, (2001). Soluble sugar concentrations and hexokinase activities were also examined during rehydration of the three species. Sucrose was accumulated during dehydration in all species examined. However, C. wilmsii had completed sucrose accumulation by the intermediate stages of drying, whereas Xhumilis exhibited a late accumulation. It was not clear if Xschlecterii exhibited late sucrose accumulation due to high standard deviations in the results. C. wilmsii accumulated higher sucrose levels than the two poikilochlorophyllous species. During rehydration the sucrose concentrations dropped in all three species, and was probably being used as an energy source for the resumption of metabolism. Glucose and fructose concentrations were relatively constant during dehydration in all three species, and did not appear to be contributing greatly to sucrose accumulation. This was further confirmed by the low levels of activity of hexokinase found in all three species during dehydration and rehydration, which suggests that the channelling of glucose and fructose into sucrose biosynthesis is not being upregulated during dehydration. C. wilmsii had an increased level of hexokinase late in dehydration, that may have been in preparation for the rapid rehydration experienced by this homiochlorophyllous species, where hexokinase would need to rapidly channel glucose and fructose into metabolism. There was not an increase in activity at the period of highest sucrose accumulation in this species. The activity of hexokinase was relatively constant throughout dehydration and rehydration for Xschlecterii, as it was for Xhumilis. Glucose and fructose levels dropped slightly in C. wilmsii during rehydration but remained relatively constant in the two poikilochlorophyllous species. The presence of LEA-like proteins was found in all three species, although the bands were very faint for X viscosa and Xhumilis. In Xschlecterii the bands were clear in the dehydrated leaf sample, but were faint or absent in the hydrated sample. It is possible that the proteins in this species were upregulated or induced by drying. A protein common to all three species in dehydrated and hydrated samples was observed between the 22.5 kDa and the 15.3 kDa molecular markers.
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Bergh, Nicola G. "Aspects of the prevention of light damage during drying and rehydration of the desiccation-tolerant grass Eragrostis nindensis." Bachelor's thesis, University of Cape Town, 1998. http://hdl.handle.net/11427/25780.
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There are two main mechanisms of desiccation-tolerance in angiosperms. Both of these (poikilochlorophylly and homoiochlorophylly) involve adaptations to prevent light-induced damage as the plants dry and rehydrate. The poikiolchlorophyllous grass E. nindensis was investigated to determine physiological responses to light during drying, and mechanisms of tolerance of dehydration. The desiccation-sensitive E. curvula was investigated simultaneously as a control in order to compare responses of tolerant and sensitive relatives. Quantum efficiency of photosystem II was determined using chlorophyll fluorescence parameters and levels of photosynthetic pigments (chlorophylls and carotenoids) and of anthocyanins were measured. Electrolyte leakage of drying and rehydrating leaves was monitored to determine the extent of damage to membranes. Quantum efficiency and photosynthetic pigment contents were reduced in both plant§ dehydrated to <2% RWC; only E. nindensis recovered to initial levels. Both plants accumulated anthocyanins but these reached greater levels in E. nindensis and were found on the entire length of the leaf. On rehydration, E. nindensis lost the anthocyanins as it reconstituted chlorophylls. Neither species showed marked increases in electrolyte leakage but E. curvula did not recover on rewatering.
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Pereira, Luciano 1981. "Resistência à seca em plântulas de espécies arbóreas da floresta estacional semidecídua." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/314924.
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Orientadores: Claudia Regina Baptista Haddad, Fernando Roberto MartinsDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: Apesar da alta pluviosidade nas florestas tropicais, há grande variação na disponibilidade hídrica para as plantas. Em escala local, essa disponibilidade pode variar dependendo da localização dos indivíduos em clareiras, sua posição no relevo e a composição do solo. Em escala regional, variações relacionadas ao volume e distribuição das chuvas, aliadas às alterações climáticas sazonais, podem também gerar diferentes condições de déficit hídrico, aumentando as taxas de mortalidade das espécies arbóreas mais sensíveis, em especial no estádio de plântula. Considerando o cenário mundial de mudanças climáticas, torna-se urgente a compreensão dos mecanismos que determinam a ecologia das comunidades das florestas tropicais, principalmente em relação aos padrões de chuvas e secas. Neste trabalho analisamos as diferentes estratégias de resistência à seca de plântulas de espécies arbóreas, com o objetivo de entender como diferentes espécies arbóreas respondem à variação da disponibilidade hídrica, de modo a conhecer como essa variação filtra as espécies e conseqüentemente contribui para organizar a comunidade florestal. No primeiro capítulo apresentamos as principais estratégias de resistência à seca e as possíveis abordagens teóricas, descritas na literatura, para plântulas de espécies arbóreas, demonstrando a importância dessas estratégias na distribuição, abundância e coexistência de espécies nas florestas tropicais. As diferenças entre as florestas tropicais úmidas e secas, pelo baixo compartilhamento de espécies e os diferentes graus de resistência à seca apresentados por espécies arbóreas, indicam uma clara diferenciação de nichos. Espécies mais resistentes à seca ocupam, com maior abundância, locais mais secos, quando comparadas às espécies mais sensíveis, tanto em escala local quanto regional. Estratégias de resistência à seca podem ser de dois tipos: de tolerância à dessecação e de evitação à dessecação. No estádio de plântula, estratégias de tolerância parecem ser mais determinantes para a resistência à seca, principalmente a presença de caracteres que conferem tolerância a baixos potenciais hídricos, como resistência à cavitação. No segundo capítulo investigamos a hipótese de que há uma relação entre a abundância de algumas espécies em locais com diferentes intensidades de sombreamento e/ou sua posição na vertente (com provável gradiente hídrico) da Floresta Estacional Semidecídua e a presença de estratégias fisiológicas de trocas de gases relacionadas à resistência à seca. Avaliamos a troca de gases, dessecação e rebrota de plantas de duas espécies tardias (Esenbeckia leiocarpa e Astronium graveolens) e duas espécies pioneiras (Croton floribundus e Aegiphila selowiana) em um experimento de seca súbita em casa de vegetação. Encontramos maior resistência à seca nas espécies com maior abundância e de estádio sucessional tardio (E. leiocarpa e A. graveolens). A resistência à seca esteve associada às menores taxas de troca de gases, e as espécies com maior aproveitamento fotossintético exibiram menor resistência à seca. Essas espécies ocorrem mais abundantemente nos sítios de ocupação menos sombreados, reforçando a teoria de uma demanda conflitante para espécies que ou investem em resistência à seca ou na capacidade de aproveitamento de luz. A disponibilidade sazonal de água, assim como a diferença de luz entre as diferentes ecounidades, pode explicar a coexistência das espécies na floresta estacional
Abstract: The rainfall is high in tropical forests, but there is great variation in water availability to plants. On a local scale, this availability may vary depending on the location of individuals in gaps, their position in the landscape and soil composition. On a regional scale, variations related to the volume and distribution of rainfall, coupled with seasonal climatic changes, can also generate different water stress conditions, increasing the mortality rates of tree species most sensitive, especially at the seedling stage. Considering the global scenario of climatic changes, it is imperative to understand the mechanisms that determine the ecology of communities of tropical forests, especially in relation to patterns of rainfall and drought. We examined different strategies of drought resistance of seedlings of tree species, to determine the organization of the community and the contribution of water availability to the selection of species in these forests. The first chapter presents a review of the principal studies available on strategies for drought resistance in seedlings of tree species and the possible theoretical approaches, demonstrating the increasing importance of these studies for understanding the processes that determine the distribution, abundance and species coexistence in tropical forests. The differences between wet and dry tropical forests, in view of the low number of species in common and the different degrees of drought resistance presented by the tree species present, show a clear differentiation of niches. Species more resistant to drought present higher abundance in drier sites, compared to more sensitive species, at local and regional levels. Strategies for drought resistance may be of two kinds: desiccation tolerance and avoidance of desiccation. In the seedling stage tolerance strategies seem to be more crucial for resistance to drought, especially the presence of characteristics that confer tolerance to low water potentials, as resistance to cavitation. In the second chapter we investigated the hypothesis that there is a relationship between the existence of abundant species only at certain sites of the semi-deciduous forest and the presence of physiological strategies of gas exchange related to drought resistance. We evaluated the gas exchange process and desiccation and regrowth of plants of four species (Esenbeckia leiocarpa, Astronium graveolens, Croton floribundus and Aegiphila selowiana), during a sudden drought experiment in a greenhouse. E. leiocarpa, A. graveolens are late-successional species and C. floribundus and A. selowiana are pioneers species. We found greater resistance to drought in the most abundant and latesuccessional species. The drought resistance was associated with lower rates of gas exchange. Species with higher photosynthetic efficiency showed lower resistance to drought. These species occur most abundantly on sites less shaded, reinforcing the theory of a trade off between investment in drought resistance and ability to use light. The seasonal availability of water, similarly to differences between light of different eco-units, can explain species coexistence in the tropical seasonal forest
Mestrado
Biologia Vegetal
Mestre em Biologia Vegetal
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Gardner, Michael Jack. "Resources for the investigation of the desiccation tolerance mechanisms of the roots of Xerophyta humilis (Bak) Dur and Schinz." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/4263.
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Bibliography: leaves 119-150.Although roots play an integral role in the sensing and amelioration of environmenatl stresses, there are no reports that specifically detail their involvement in the desiccation tolerance mechanisms of resurrection plants. Very lttle is known about even the genral anatomy and physiology of the roots of plants such as X. humilis, and almost nothing about the molecular responses that confer their ability to survive desiccation. This report details foundational studies of the functional anatomy and large-scale molecular responses of the roots during dehydrtion and rehydration.
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Peng, Xiaobing Carleton University Dissertation Biology. "The role of abscisic acid and abscisic acid-analogs in inducing desiccation tolerance in microspore-derived embryos of Brassica Napus." Ottawa, 1994.
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Burdine, Justin D. "Factors influencing bee communities and pollination services across an urban environment." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1554460864439054.
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Moore, John Paul. "The role of polyphenols and the cell wall in relation to the desiccation tolerance of the resurrection plant, Myrothamnus flabellifolia (Welw.)." Doctoral thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/4299.
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Includes bibliographical references (p. 160-191).Resurrection plants are unique in that their vegetative tissue has the ability of survive reversible dehydration to an air-dry state. The widespread African resurrection plant Myrothamnus flabellifolia (Welw), woody shrub, is one of the largest of these plants. In addition to its resurrection ability it is also an important medicinal plant and is used by local tribes in the various regions where it grows to treat a wide variety of ailments. This thesis has investigated a number of morphological, ultrastructural and biochemical adaptations of the leaves of M. flabellifolia to dessication and associated stresses. The main aim of this thesis was to ascertain the role of polyphenols and the cell wall of M. flabellifolia in relation to its desiccation tolerance.
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Abu, Sharkh Sawsan E. "Spectroscopic & thermodynamic investigations of the physical basis of anhydrobiosis in caenorhabditis elegans dauer larvae." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-164661.
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Anhydrobiotic organisms have the remarkable ability to lose extensive amounts of body water and survive in an ametabolic, suspended animation state. Distributed to various taxa of life, these organisms have evolved strategies to efficiently protect their cell membranes and proteins against extreme water loss. At the molecular level, a variety of mutually non-exclusive mechanisms have been proposed to account particularly for preserving the integrity of the cell membranes in the desiccated state. Recently, it has been shown that the dauer larva of the nematode Caenorhabditis elegans is anhydrobiotic and accumulates high amounts of trehalose during preparation for harsh desiccation (preconditioning), thereby allowing for a reversible desiccation / rehydration cycle.
Here, we have used this genetic model to study the biophysical manifestations of anhydrobiosis and show that, in addition to trehalose accumulation, the dauer larvae exhibit a systemic chemical response upon preconditioning by dramatically reducing their phosphatidylcholine (PC) content. The C. elegans strain daf-2 was chosen for these studies, because it forms a constitutive dauer state under appropriate growth conditions. Using complementary approaches such as chemical analysis, time-resolved FTIR-spectroscopy, Langmuir-Blodgett monolayers, and fluorescence spectroscopy, it is shown that this chemical adaptation of the phospholipid (PL) composition has key consequences for their interaction with trehalose. Infrared-spectroscopic experiments were designed and automated to particularly address structural changes during fast hydration transients.
Importantly, the coupling of headgroup hydration to acyl chain order at low humidity was found to be altered on the environmentally relevant time scale of seconds. PLs from preconditioned larvae with reduced PC content exhibit a higher trehalose affinity, a stronger hydration-induced gain in acyl chain free volume, and a wider spread of structural relaxation rates during lyotropic transitions and sub- headgroup H-bond interactions as compared to PLs from non-preconditioned larvae. The effects are related to the intrinsically different hydration properties of PC and phosphatidylethanolamine (PE) headgroups, and lead to a larger hydration-dependent rearrangement of trehalose-mediated H-bond network in PLs from preconditioned larvae. This results in a lipid compressibility modulus of ∼0.5 mN/m and 1.2 mN/m for PLs derived from preconditioned and non-preconditioned larvae, respectively.
The ensemble of these changes evidences a genetically controlled chemical tuning of the native lipid composition of a true anhydrobiote to functionally interact with a ubiquitous protective disaccharide. The biological relevance of this adaptation is the preservation of plasma membrane integrity by relieving mechanical strain from desiccated trehalose- containing cells during fast rehydration. Finally, the thermo-tropic lipid phase behavior was studied by temperature-dependent ATR-FTIR and fluorescence spectroscopy of LAURDAN-labeled PLs. The results show that the adaptation to drought, which is accomplished to a significant part by the reduction of the PC content, relies on reducing thermo-tropic and enhancing lyotropic phase transitions. The data are interpreted on a molecular level emphasizing the influence of trehalose on the lipid phase transition under biologically relevant conditions by a detailed analysis of the lipid C=O H-bond environment.
The salient feature of the deduced model is a dynamic interaction of trehalose at the PL headgroup region. It is proposed here that the location of trehalose is changed from a more peripheral to a more sub-headgroup-associated position. This appears to be particularly pronounced in PLs from preconditioned worms. The sugar slides deeper into the inter-headgroup space during hydration and thereby supports a quick lateral expansion such that membranes can more readily adapt to the volume changes in the swelling biological material at reduced humidity. The data show that the nature of the headgroup is crucial for its interaction with trehalose and there is no general mechanism by which the sugar affects lipidic phase transitions. The intercalation into a phosphatidylethanolamine-rich membrane appears to be unique.
In this case, neither the phase transition temperature nor its width is affected by the protective sugar, whereas strong effects on these parameters were observed with other model lipids. With respect to membrane preservation, desiccation tolerance may be largely dependent on reducing phosphatidylcholine and increasing the phsophatidylethanolamine content in order to optimize trehalose headgroup interactions. As a consequence, fast mechanical adaptation of cell membranes to hydration-induced strain can be realized.