Dissertations / Theses: 'Desiccation'

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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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Bohnert, Hans J. "What makes desiccation tolerable?" BioMed Central, 2000. http://hdl.handle.net/10150/610140.

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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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Wortmann, Heid. "Sedimentation and desiccation of gold mines." Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-11052007-152710.

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Atique, Alvis. "Investigation of desiccation cracks in drying soil." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=20835.

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This research investigates desiccation cracking behaviour of a fill material from a flood embankment along the Bengawan Solo River in East Java, Indonesia, an area that is prone to extremes in flooding and drying. A detailed study of the previous works on this topic showed the absence of fully-monitored laboratory tests dedicated to desiccation cracking behaviour. This study combined traditional and new techniques to characterise desiccation cracking behaviour in this material in a suite of laboratory tests. Desiccation plate tests were conducted to gain basic knowledge of the cracking behaviour of Bengawan Solo soil and identify the influences of plate shape on test results. Crack initiation, evolution, and final pattern were studied in detail. Results of the experiments showed that plate geometry had minimal effect on cracking behaviour except for the final cracking pattern. Crack initiation and evolution was characterised with a 2D/3D profile laser sensor coupled to a motion controller that allowed scanning of the overall surface of the drying soil. The system developed for this work was used to track the three most relevant variables associated with the behavior of soils during desiccation: volume change, water loss, and evolving crack network morphology. With this new method, the evolution of crack aperture, crack depth, surface contour levels (settlements) and evolution of global volume change were captured in real time, significantly improving upon previous methods for crack monitoring. Finally, the effects of moisture content and dry density on tensile strength during cracking was investigated at two states: reconstituted and compacted. Microstructural investigation illustrated the fabric changes during drying at two states to complement the experimental results for tensile strength. The comparison of tensile strength between reconstituted and compacted state has been found promising and believed to be useful in earthwork construction projects.

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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 references
Resurrection 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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Mohammad, Noor. "Desiccation Cracking Behaviour in Thin Bentonite Layers." Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/22231.

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This thesis investigates the behaviour of desiccation cracks in thin bentonite layers under different conditions (initial water content, layer thickness, temperature and mixtures with kaolinite). For this, a comprehensive series of experiment was conducted as well as some theoretical models were developed. The theoretical model was developed based on the critical cracking thickness following the principles of linear elastic fracture mechanics (Chapter 4). This model was then used in the following chapters and validated with the experimental investigations. Also, hydraulic properties of the cracked soil mass were modelled and the effects of cracks on hydraulic conductivity and water retention properties were shown. In the experimental investigations, firstly, the combined effects of initial water content and layer thickness were studied in a phase diagram to observe the behaviour of desiccation cracks (Chapter 5). It was found that critical cracking thickness could be an important factor in distinguishing cracked and non-cracked samples in the phase diagram. Characteristics of cracks (crack density, total crack length, average crack length and crack width) increase with increasing layer thicknesses as well as initial water contents. The effects of temperature (Chapter 6) and mixtures of bentonite-kaolinite (Chapter 7) on desiccation cracking were investigated in the phase diagram developed in Chapter 5. At higher temperatures, the critical thickness of a clay layer ould be decreased. Results of bentonite-kaolinite mixture demonstrated that the phase boundary shifted to increase the critical thickness of the clay layers of mixtures containing less bentonite (i.e. more kaolinite). Crack morphology was also affected by the change in temperatures and properties of the mixtures. In summary, this study shows some understanding of desiccation cracking behaviour and could provide insights for better design of clay liners, which often at risk of desiccation problem.

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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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10

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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Stirling, Ross Alexander. "Multiphase modelling of desiccation cracking in compacted soil." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2492.

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The development of cracking as a result of desiccation is increasingly under investigation. This work is set within the context of climate change effects on surface processes influencing infrastructure slope stability. The inherent changes to the mechanical and hydrological behaviour of clayey soils subjected to desiccation are significant. The preferential transmission of water due to cracking is widely cited as a source of strength reduction that leads to infrastructure slope failure. In order to gain a better understanding of the cracking mechanism in typical compacted fill conditions, finite difference continuum modelling has been undertaken using FLAC 2D. The two-phase flow add-on has enabled the unsaturated behaviour of the desiccating soil to be included within the mesh. Physical behaviour observed in laboratory experiments has informed the development of the numerical model by allowing better constraint of boundary conditions. Model development has featured the inclusion of several non-linear processes that are fundamental to the changing soil response during drying. The influence of significant parameters has been identified and by means of a varied experimental program, the design, manufacture and testing of a laboratory test apparatus and procedure to define the tensile strength of compacted fills under varying saturation conditions was undertaken and subsequently validated. The factors affecting crack initiation and propagation have been investigated via parametric study. This demonstrated the significant influence of basal restraint on the generation of tensile stresses conducive to cracking and the fundamental importance of the tensile strength function within the proposed modelling methodology. Experimentation with the shape of the SWRC has shown the model to be very sensitive to the hydraulic properties of the material with not only the occurrence of primary cracking being affected but also the development of the desiccated crust. The findings of this work are relatable to the incorporation of desiccation effects in the development of coupled hydrological-mechanical continuum models where atmosphere-soil interactions are increasingly significant.

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Harland, Christopher William 1983. "Desiccation resistance and viscoelasticity in model membrane systems." Thesis, University of Oregon, 2010. http://hdl.handle.net/1794/10993.

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xii, 89 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
Lipid membranes are a basic structural element of all cells. They provide a framework for the physical organization of the cell, act as a scaffold for numerous proteins, and serve as the host site for countless chemical reactions integral to cell function. Several key problems in membrane biophysics hinge on reliable methods for measuring membrane material properties. Properties such as rigidity, fluidity, charge density, etc., are important factors that govern membrane structure and function. As such, we need controllable, reliable, and quantitative methods of probing membrane material properties. In pursuit of such methods, we completed two related projects that, while distinct, aimed to create and apply quantitative measures of membrane material properties to current problems in biophysics. The first of these two lines of inquiry centered on the pervasive, pathogenic family of mycobacteria that is known to not only cause several diseases but also to survive prolonged periods of dehydration. We developed an experimental model system that mimics the structure of the mycobacterial envelope consisting of an immobile hydrophobic layer supporting a two-dimensionally fluid, glycolipid-rich outer monolayer. With this system, we show that glycolipid containing monolayers, in great contrast to phospholipid monolayers, survive desiccation with no loss of integrity, as assessed by both fluidity and protein binding, revealing a possible cause of mycobacterial persistence. In the second line of inquiry, we developed another general platform for probing membrane material properties that has produced the first reported observations of viscoelasticity in lipid membranes. We utilized recently developed microrheological techniques on freestanding lipid bilayer systems using high speed video particle tracking. The complex shear modulus of the bilayers was extracted at a variety of temperatures that span the liquid-ordered to disordered phase transition of the membranes. At many temperatures measured, the membranes displayed viscoelastic behavior reminiscent of a Maxwell material, namely elastic at high frequencies and viscous at low frequencies. Moreover, the viscoelastic behavior was suppressed at the critical phase transition temperature where the membranes behave as a purely viscous fluid. Surprisingly, the viscoelastic behavior was found in all of several distinct membrane compositions that were examined.
Committee in charge: Dr. Daniel Steck, Chair; Dr. Raghuveer Parthasarathy, Research Advisor; Dr. Darren Johnson; Dr. Heiner Linke; Dr. John Toner

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15

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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Fan, Cynthia. "Characterisation of two desiccation-linked dehydrins from Xerophyta humilis." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22723.

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In response to abiotic stresses, organisms throughout the plant kingdom, as well as microorganisms and micro-animals such as nematodes or tardigrades, have been observed to express Late Embryogenesis Abundant (LEA) proteins as protective mechanisms. However, despite two decades of research, little is understood about their physiological functions and this has led to extensive nomenclature, with a large amount of redundancy. The primary reason for this lack of insight into LEA protein functions is their highly hydrophilic and intrinsically disordered nature. Intrinsically disordered proteins (IDPs) cannot be studied using conventional methods of structural analyses such as X-ray crystallography and, therefore, alternative techniques are required. A combination of transgenic and in vitro studies have also shown that LEA proteins are most likely to behave as molecular chaperones by binding water and ions, preventing macromolecular aggregation and protecting enzymatic activity during dehydration. This study characterized two dehydrins that were expressed during dehydration in the desiccation tolerant plant, Xerophyta humilis. From a transcriptome analyses on X. humilis, cDNA for the two dehydrins were obtained. These sequences were first analysed using various in silico tools in order to identify putative dehydrin-specific characteristics. Subsequently, these two dehydrins were cloned and expressed for production of recombinant dehydrin protein. These proteins were then analysed in terms of structural and functional characteristics. Structurally, through the use of circular dichroism in an in vitro system, both dehydrins demonstrated the shift towards being increasingly alpha-helical when placed in environments of decreasing water content. The role of these two dehydrins in stabilizing enzymes during dehydration was subsequently investigated using citrate synthase (CS) and lactate dehydrogenase (LDH). The preservation of enzyme activity was observed in both CS and LDH. This preservation of enzyme activity was further maintained by the presence of trehalose. Anti-aggregation roles were also investigated, however, neither dehydrin demonstrated significant ability to minimize the aggregation of LDH. This study hopes to establish a pipeline for characterizing LEA proteins using structural and functional assays in order to provide alternative means of LEA protein classification.

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Mayer, Melinda Jane. "Gene expression during late embryogenesis in pea (Pisum sativum L)." Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5722/.

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A thesis submitted by Melinda Jane Mayer, B.Sc.(Bristol) in accordance with the requirements of the University of Durham for the degree of Doctor of Philosophy. Department of Biological Sciences, August 1993.Two cDNA libraries were constructed from desiccating pea cotyledons. Differential screening of the libraries with cDNA from an earlier developmental stage (physiological maturity) demonstrated that the abundant message population during dehydration shows some noticeable differences to the message populations present before desiccation. Clones hybridising to a polyubiquitin probe were isolated from a cDNA library. These clones were identified as messages for the two types of ubiquitin extension proteins (with 52 and 79 residue tails), already characterised in other species as being involved in ribosome biogenesis. The pea ubiquitin extension tail amino acid sequences showed considerable homology to tails from other plants, animals, yeast and protozoa, including a nuclear localisation site and a putative zinc-binding nucleic acid binding domain, the positions of which are conserved within the tail sequences. Sequencing of a second polyubiquitin cDNA from pea leaf demonstrated that pea contains a ubiquitin multigene family of at least four members. The expression of several genes associated with plant response to stress and two abundant seed messages (Leg A and J) was examined in developing and dehydrating cotyledons and axes. This confirmed conspicuous variations in the message levels of the genes examined as the cotyledons aged, with different members of the ubiquitin and legumin multigene families showing differential expression with age. It was also demonstrated that the expression pattern of certain messages in the cotyledons was different to that in the axes and other seed tissues. This was confirmed by an analysis of total and albumin protein fractions in cotyledons and axes. The effect on specific message and protein levels of premature desiccation treatments indicated that the temporal expression of several seed genes is related to the state of hydration of the seed, artificial desiccation leading to premature maturation. Seed storage protein message and protein levels were especially increased by premature desiccation. Legumin seed storage protein messages were also shown to be responsive to exogenous ABA applied to immature cotyledons during the seed filling stage. However, the other stress-related messages examined in pea (ubiquitin and a pea putative metallothionein) were not responsive to exogenous ABA at this developmental stage.

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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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Roca, Domènech Gemma. "Characterization of non-Saccharomyces wine yeasts during desiccation stress imposition." Doctoral thesis, Universitat Rovira i Virgili, 2018. http://hdl.handle.net/10803/664712.

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L’objectiu principal d’aquest estudi és la caracterització fisiològica de llevats vínics no-Saccharomyces sota l’estrès de deshidratació. Actualment, els Llevats Vínics Secs Actius (LVSA) són extensament usat per la producció de vi, degut a la seva estabilitat genètica a temperatura ambient, reduint costos de transport i emmagatzematge. A més, els llevats no-Saccharomyces cada cop són més estudiats degut al seu potencial per a la producció de vi, tant en combinació amb Saccharomyces cerevisiae, com no. Vam desenvolupar protocols per obtenir LVSA de Starmerella bacillaris i Schizosaccharomyces pombe, incrementant de forma significativa la viabilitat assecant les cèl·lules en presència de trehalosa i rehidratant amb rafinosa/galactosa o magnesi, respectivament. Observant l’efecte del magnesi en Schiz. pombe després de l’assecatge, vam realitzar una caracterització metabolòmica de Schiz. pombe, observant que l’acumulació del metabòlit 5’-metiltioadenosina durant la rehidratació amb magnesi participava en l’increment de la tolerància al assecat de Schiz. pombe i prevenia la toxicitat produïda per la síntesi de poliamines. Tanmateix, la tolerància a la deshidratació causada per l’ió magnesi en Schiz. pombe no és un fenotip resultant d’una via metabòlica concreta. També vam avaluar l’efecte de la suplementació amb magnesi en fermentacions tradicionals i en fermentacions amb una reduïda concentració de sucres constant. Tot i que no s’observava cap efecte del magnesi en el desenvolupament de les fermentacions, el manteniment dels sucres constant al llarg de les fermentacions va permetre la reducció dràstica dels nivells residuals d’àcid acètic mantenint nivells de glicerol relativament elevats.
El objetivo principal de este estudio es la caracterización fisiológica de levaduras vínicas no-Saccharomyces sometidas al estrés de secado. Actualmente, las Levaduras Vínicas Secas Activas (LVSA) son extensamente usadas para la producción de vino, debido a su estabilidad genética a temperatura ambiente, reduciendo costes de transporte y almacenaje. Además, las levadura no-Saccharomyces cada vez son más estudiadas debido a su potencial para la producción de vino, tanto en combinación con Saccharomyces cerevisiae, como no. Desarrollamos protocolos para obtener LVSA de Starmerella bacillaris y Schizosaccharomyces pombe, aumentando de forma significativa la viabilidad secando las células en presencia de trehalosa y rehidratando con rafinosa/galactosa o magnesio, respectivamente. Observando el efecto del magnesio en Schiz. pombe después del secado, realizamos una caracterización metabolómica de Schiz. pombe, observando que la acumulación de 5’-metiltioadenosina durante la rehidratación con magnesio participaba en el incremento de la tolerancia al secado de Schiz. pombe y prevenía a la toxicidad producida por la síntesis de poliaminas. Sin embargo, la tolerancia a la deshidratación causada por el ión magnesio en Schiz. pombe no es un fenotipo resultante de una ruta metabólica concreta. También se evaluó el efecto del magnesio durante fermentaciones tradicionales y en fermentaciones con reducida concentración de azúcares constante. A pesar de que los resultados no mostraron ningún efecto del magnesio en el desarrollo de las fermentaciones, el mantenimiento de los azúcares constantes a lo largo de las fermentaciones permitió la reducción drástica de los niveles residuales de ácido acético manteniendo niveles de glicerol relativamente elevados.
The main target of this study has been the physiological characterization of non-Saccharomyces wine yeasts under desiccation stress imposition. Nowadays, active dry wine yeasts (ADWY) are the most widely used in winemaking due to its genetic stability at room temperature, reducing transport and storage costs. In addition, non-Saccharomyces wine yeasts are being increasingly investigated with regards to their grape winemaking potential either in combination with the typical production yeast, Saccharomyces cerevisiae, or in monoseptic fermentations. We developed ADWY protocols for Starmerella bacillaris and Schizosaccharomyces pombe strains, resulting in a significant enhancement of viability when cells are dried in the presence of trehalose, followed by rehydration with raffinose/galactose or magnesium, respectively. Since magnesium rehydration increases the Schiz. pombe viability after a desiccation stress, we performed a metabolomics characterization in Schiz. pombe, observing that 5’-methylthioadenosine metabolite accumulation by magnesium rehydration participates in the enhancement of Schiz. pombe desiccation stress tolerance and prevents the toxicity produced by polyamines synthase in cells restarting growth. However, the dehydration stress tolerance driven by the ion magnesium in Schiz. pombe is not a phenotype resulting from an individual metabolic pathway. We also investigated the effect of magnesium supplementation in traditional and in fed-batch fermentations. Although our results did not show that magnesium have any effect of the Schiz. pombe fermentation performance, the application of the fed-batch techniques allows a drastically reduction of the residual acetic acid levels maintaining relatively high levels of glycerol.

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Zieliński, Marcin. "Influence of desiccation fissuring on the stability of flood embankments." Thesis, University of Strathclyde, 2009. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=22000.

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It has been known since studies carried out by Cooling and Marsland for the 1953 North Sea Floods that desiccation fissuring of clay fill can play a major role in the failure of flood embankments under overflow conditions. However, very little scientific research has been carried out into the onset of desiccation fissuring in flood embankments and the potential failure mechanisms. To overcome this shortage of information, field and laboratory studies have been carried out into the desiccation fissuring of clay fill for flood embankments. The preliminary results confirmed that desiccation fissuring occurs to a depth of typically 60 cm within the outer surface of a flood embankment constructed from clay fill and can occur within 2 years of construction. The critical condition occurs when desiccation creates an interconnected network of sub-vertical and sub-horizontal fissures that increases the mass permeability of the fill material similar to that of coarse sand or gravel and hence allows rapid seepage of flood water through the surface layer of the embankment (crest and sides slopes). The aim of the thesis is to investigate the influence of desiccation fissuring on the stability of flood embankments. In particular, the main objectives of this thesis are as follows: 1. Survey of flood embankments in UK constructed from clay fill to determine the extent and nature of desiccation fissuring. 2. Construction and investigation of the behaviour of macro-scale embankmenmt odel subjected to desiccation processes. 3. Investigation of the innovative, non-invasive geophysical technique for desiccation cracking detection. 4. Investigation of the embankment model behaviour under different flooding conditions.

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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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Cannell, Elizabeth. "Neuroendocrine and metabolic responses to desiccation stress in Drosophila melanogaster." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/7120/.

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Insects are highly successful and their large numbers lead to economic loss through crop damage and disease transmission. Insecticides provide a valuable tool for control of insect populations. However, as resistance is increasing to existing products, new modes of action are required for the development of novel products. Understanding of the biological mechanisms underlying stress resistance in insects may provide insight into new potential insecticide targets. Malpighian tubules are critical for epithelial fluid transport and xenobiotic tolerance in insects. The function of Malpighian tubules in desiccation stress tolerance was explored by examining changes in gene expression, protein levels, fluid transport rates, and metabolism following stress exposure. The results indicate a reduction in secretion rate during desiccation that is reflected in accumulation of metabolites that are normally processed and excreted by the tubules. Moreover, the involvement of Drosophila melanogaster diuretic hormones corticotrophin releasing factor-like (DH44) and leucokinin (LK) were examined using genetic manipulations based on the GAL4-UAS system. Highly selective manipulation of the DH44-producing neurons via knockdown of DH44 and neuronal ablation indicates that suppression of DH44 signalling contributes to desiccation tolerance. This result is supported by the finding that knockdown of DH44 receptor 2 in the Malpighian tubule principal cells improves survival during desiccation stress. Previous work suggests the possibility of interaction between LK and DH44 signalling as LK receptor (LKR) is colocalised to the DH44 neurons. This hypothesis is supported by the results of this study as selective knockdown of LKR and DH44 in the DH44 neurons produced opposing effects on desiccation tolerance. Moreover, knockdown of DH44 in the DH44 neurons or ablation of these neurons resulted in significantly decreased LKR expression in the Malpighian tubules. Finally, a novel role for the Malpighian tubules in starvation tolerance was uncovered by the study, with LKR gene expression increasing significantly following starvation. Knockdowns of either DH44-R2 or LKR in the Malpighian tubules significantly impaired starvation tolerance. Here, a mechanism for this role of renal epithelia in starvation tolerance is proposed.

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Hoffmann, Heiko. "The dynamics of crack patterns in soil induced by desiccation." [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10633918.

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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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Eminue, Oboho Okon. "Environmental and material controls on desiccation cracking in engineered clay embankments." Thesis, University of Newcastle upon Tyne, 2018. http://hdl.handle.net/10443/4101.

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Desiccation cracking is a natural phenomenon commonly associated with drying of expansive soils. The role of cracks in surface permeability increase and overall deterioration of infrastructure slopes makes it a key factor in climate-related slope instability processes. Despite this significance, the controls on soil cracking in engineered slopes still represent a poorly understood area. In this study, soil cracking behaviour in clay embankments exposed to cyclic wetting and drying was investigated to improve understanding of this phenomenon for application in geotechnical practice. A complimentary field and laboratory study was undertaken, approaches commonly conducted in isolation in the literature. The field program involved direct investigation of natural crack development in a heavily instrumented, clay embankment (BIONICS, Newcastle University). Crack morphology parameters were quantified under engineering, meteorological and near surface soil hydrological conditions to understand how temporal change influences these. Laboratory experimentation was carried out on materials representative of typical embankment fills and construction methods in the UK in a bespoke climate control system. Time series photographs of the crack networks were analysed using image processing technique to compare their intensities across the experimental conditions. Syntheses of field and laboratory results show the influence of factors related to the embankment geometry (i.e. slope aspect, layer thickness), material properties (i.e. soil density and plasticity) and environmental condition (i.e. wetting and drying cycles) on the cracking behaviour in engineered clay slopes. The sensitivity of cracking intensity under given climate conditions critically relates to the rate of moisture loss and the material strength. Overall, this research presents how newly gained understanding of cracking can potentially impact upon improved construction techniques of engineered clay embankments and the susceptibility of historic embankments constructed to lower densities to climatic changes, including how drying/wetting cycles can exacerbate crack development.

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Booth, Andrew. "Impacts of desiccation cracking and climate change on highway cutting hydrology." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/14825.

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Climate change is predicted to have a global effect on temperatures and precipitation rates throughout the world. The UK Climate projections expect that in the United Kingdom this will lead to warmer, drier summers and wetter winters, where events of extreme rainfall are more common. These changes are expected to impact on slope hydrology, and concurrently slope stability. In the United Kingdom this impact is expected to be negative, whereas in other countries, such as Italy and France it could lead to slopes being more stable. Infrastructure slopes in the UK range in age and construction quality, they are susceptible to serviceability problems, characterised by heterogeneous material properties and can fail unexpectedly due to progressive reduction in soil shear strength. In this thesis the effects of climate change on a highway cutting in the south of England are modelled, using numerical methods. A finite element model is created and developed in the software package GeoStudio VADOSE/W. The model has been validated against observed pore water pressure trends and magnitudes and is shown to be able to accurately replicate the behaviour. By incorporating the effects of desiccation cracking on the soil s material properties, by the means of bimodal soil water characteristic curve and hydraulic conductivity function, the replication of these trends is improved even further. A series of future climate series were created using the UKCP09 Weather Generator 2.0. These series were implemented with the VADOSE/W model as climate boundary conditions and models were run, and the results compared to control, current climate results. The results were investigated by the means of statistical analyses which revealed that climate change will have some significant effects on the slope s hydrology, increasing magnitudes of evapotranspiration greatly which can have further significant effects on the magnitude of suctions developing in the slope throughout the summer. It is thought that the results suggest that climate change will not have significant negative effects on slope stability. However it is important to remember that the results only apply with certainty to the specific slope and climate change scenario investigated here. The methods used and developed within this thesis can be extended to other locations, in the UK and internationally, analysing the effects of different climate change scenarios.

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Garst, James Frazier. "Physiological and Biochemical Response of Saccharomyces cerevisiae to Desiccation and Rehydration." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/32918.

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Baker's yeast (Saccharomyces cerevisiae) undergoes major biochemical and structural rearrangements in order to survive cycles of desiccation and rehydration, yet a firm understanding of the response is lacking. The purpose of this study was to examine the response of S. cerevisiae to desiccation and rehydration at both the physiological and molecular levels. Transmission electron microscopy was used to show that loss of vacuolar structure, enlarged nuclear boundaries, as well as cell wall thickening were all associated with the desiccation response. Molecular analysis focused on glyceraldehyde-3-phosphate dehydrogenase (GAPDH, E.C. 1.2.1.13), a multifunctional protein that is involved in several cellular processes other than glycolysis, including nuclear translocation under stress and intracellular sensing of oxidative stress during apoptosis. Here, GAPDH was studied primarily to determine its potential role in mediating the changes in cell wall physiology identified through our structural studies. GAPDH appears to be shuttled between the cell wall and the cytoplasm during the desiccation/rehydration process. Western analyses in combination with the use of inhibitors of translation (cycloheximide) suggest that the shuttling process does not require de novo protein synthesis. Western analyses also identified an immuno-reactive peptide in the cell wall and cytoplasmic fractions of lower molecular mass than native GAPDH (27 KDa vs. 37 KDa). This lower molecular weight peptide exhibited the translocation process similar to that of the full length GAPDH. Studies with GAPDH deletion strains suggested that the 27 kDa fragment is encoded by tdh3. The importance of this lower molecular weight form is yet to be determined.
Master of Science in Life Sciences

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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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Lehmann, Philipp Nicolas. "Changing Climates: Deserts, Desiccation, and the Rise of Climate Engineering, 1870-1950." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13070077.

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This dissertation examines the impact of the nineteenth-century discussions about climate change and desiccation on large engineering projects in desert regions between 1870 and 1950. It demonstrates that the debate over the variability of global climatic conditions was a product of both internal academic and transnational political developments, and that the perceived threat of advancing desert conditions found a popular and technocratic expression in climate engineering designs. Against the background of new theories about the earth's geological history, the development of academic geography, the travels of Sahara explorers, and imperialism in North Africa, European geographers and geologists initiated an enduring discussion on the origin of desert environments and the question of large-scale climatic changes in the recent past and present. Using a wide array of evidence ranging from cave paintings found in the interior Sahara and classical travel accounts to modern meteorological data, scientists debated whether North Africa, the entire continent, or even the whole world were undergoing desiccation. While the lack of a widely-accepted causal mechanism behind large climatic changes meant that the academic debate remained unresolved by the beginning of the twentieth century, images of progressing desert conditions had already left the confines of academia, heightening public anxiety over the possibility of future climatic catastrophes on a global scale. From the early stages of the nineteenth-century debate on climate change, fears of desiccation inspired scientists and engineers to come up with solutions to detrimental climatic shifts, whether these were viewed as man-made or natural. The resulting climate engineering projects were an expression of environmental pessimism paired with a powerful technological optimism. This was apparent in French and British schemes in the late nineteenth century that aimed to flood large parts of the Sahara and effect wide-ranging climatic changes; in the plan of a German architect to engineer a geographically and climatically transformed new Euro-African continent in the 1920s; and eventually in Nazi designs to Germanize and green the "desertified" areas of Eastern Europe and Central Asia.
History

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VILLAR, LUCIO FLAVIO DE SOUZA. "RESEARCH ON CONSOLIDATION AND DESICCATION OF BAUXITE MINING AND INDUSTRIAL PROCESSING WASTES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2002. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=3528@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Este trabalho apresenta a metodologia usada no acompanhamento do adensamento e do ressecamento de resíduos de mineração e processamento de bauxita, as lamas vermelhas. A proposta foi investigar métodos para obtenção de informações sobre efeitos do ressecamento solar no comportamento da lama, buscando identificar a transição da fase saturada para a não saturada destes materiais. A pretensão foi facilitar a incorporação destes efeitos a métodos de análise do ciclo de vida útil de reservatórios de disposição de rejeitos de mineração e processamento depositados sob forma de lama, e que em geral só consideram os recalques por peso próprio e/ou lançamento de novas camadas. Será possível, então, chegar a uma previsão mais realista de sua capacidade de armazenamento e de suas características finais, dados importantes para executar projetos mais racionais de reabilitação do depósito. Foram estudados cinco tipos de resíduos diferentes. Um, é constituído pelos rejeitos de lavagem de bauxita de uma mina localizada no estado do Pará, sendo composto somente de grãos sólidos e água. O segundo tipo é o resultado do processamento deste primeiro material, uma lama com fluido altamente básico (pH 14). Os outros dois são rejeitos de processamento de bauxitas de duas regiões diferentes do estado de Minas Gerais: um da região de Poços de Caldas, e o outro, da região de Ouro Preto, ambos com pH em torno de 14. Este último material, da região de Ouro Preto, é que foi utilizado em estudos anteriores da PUCRio. O último resíduo analisado é produto de uma neutralização feita nesta mesma lama de Ouro Preto antes de sua disposição final. Foram com estes dois últimos rejeitos que se realizou a maior quantidade de testes e análises, e eles, então, se constituíram os objetos principais da pesquisa. Foram executados ensaios de adensamento com deformação controlada, determinação de curvas características de sucção e secagem através de diferentes técnicas (papel filtro, tensiômetros etc); caracterizações especiais e ensaios de ressecamento em caixas de dimensões variadas, procurando simular o efeito da radiação solar nestes rejeitos, e ensaios de campo (medição de poropressões e coleta de amostras). Metodologias de execução e interpretação destes testes para estes materiais não usuais são propostos. O seu comportamento na transição da fase saturada para a não saturada foi acompanhado, tanto com relação à variação de volume quanto de resistência. Modelos empíricos são sugeridos, e podem ser usados para uma primeira previsão dos efeitos da exposição à secagem.
This work presents the methodology used to study the consolidation and desiccation of bauxite wastes from mining and industrial processing. The aim is to understand the geotechnical behavior of these wastes launched as slurries in reservoirs and then, let do dry under solar exposure. Five types of residues are here considered. The first is an inert waste resulting from washing of bauxite in mining operations run in the North of Brazil. The other four are wastes resulting from the physicochemical treatment of the bauxite in alumina production industrial plants. Such treatment follows the worldwide known Bayer process. Three of these four wastes, which are usually named as red muds, are disposed with pH around 14. The other one is disposed after neutralization with sulfuric acid, under a pH around 8. Data of solar exposure effects on the muds behavior was obtained in order to determine parameters to be incorporated into consolidation models. Therefore, an improvement on predictions of the life cycle of the wastes reservoirs can be achieved. To study the transition between the saturated phase to the unsaturated one and to determine the geotechnical and geomechanics characteristics of the wastes, an extensive laboratory testing program was performed. This included CRD tests, monitored physical model tests and the determination of water retention curves for the wastes from fully wetted to dry conditions. Laboratory results are compared with those of field monitoring programmes and some empirical models are proposed.

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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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Radermacher, Astrid Lillie. "Desiccation-driven senescence in the resurrection plant Xerophyta schlechteri (Baker) N.L. Menezes." Doctoral thesis, Faculty of Science, 2019. https://hdl.handle.net/11427/31708.

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Drought-induced senescence is a degenerative process that involves the degradation of cellular metabolites and photosynthetic pigments and uncontrolled dismantling of cellular membranes and organelles. Angiosperm resurrection plants display vegetative desiccation tolerance and avoid drought-induced senescence in most of their tissues. Developmentally older tissues, however, fail to recover during rehydration and ultimately senesce. Comparison of the desiccation-associated responses of older senescent tissues (ST) with non-senescent tissues (NST) will allow for understanding of mechanisms promoting senescence in the former and prevention of senescence in the latter. In the monocotyledonous resurrection plant Xerophyta schlechteri (Baker) N.L.Menezes, leaf tips senesce following desiccation, whereas the rest of the leaf blade survives. This study characterised structural, metabolic and transcriptional changes in ST and NST at varying water contents during desiccation and rehydration. Light and transmission electron microscopy was used to follow anatomical and subcellular responses, and metabolic differences were studied using gas chromatography-mass spectrometry and colorimetric metabolite assays. These results show that drying below 35% relative water content (0.7 gH2O/g dry mass) in ST resulted in the initiation of age-related senescence hallmarks and that these tissues continue this process after rehydration. Analysis of the transcriptome was done using RNA-Seq, which was subject to differential expression analysis and network analysis to elucidate the potential mechanisms for senescence regulation in this species. Significantly increased transcription of senescence associated genes was observed in the air dry sampling point, indicating that initiation of cellular death occurred below 20% RWC. Network analysis based on Pearson correlation revealed a high degree of clustering of these genes, suggesting co-regulation. The majority of these genes had two enriched motifs in their upstream regions, identified as binding sites for WRKY and other transcription factors. A model integrating these observations is presented, with insights into how senescence is initiated in ST and repressed in NST.

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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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Fazel, Modares N. (Nasim). "The role of climate and land use change in Lake Urmia desiccation." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526221021.

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Abstract Wetlands in arid and semi-arid regions are complex fragile ecosystems that are critical in maintaining and controlling environmental quality and biodiversity. These wetlands and specially closed lake systems depend on support processes in upstream parts of the basin or recharge zone, as small changes in river flow regime can cause significant changes in lake level, salinity and productivity. Recent strong alterations in river flow regimes due to climate and land use change have resulted in ecosystem degradation and desiccation of many saline lakes in arid and semi-arid regions. Because of the low economic value of these lakes, their hydrology has not been monitored accurately, making it difﬁcult to determine water balance and assess the role of water use and climate in lake desiccation. Furthermore, available data are usually of coarse resolution on both spatial and temporal scale. New frameworks using all available data and refining existing information on lake basins were developed in this thesis to assess regional differences in water resource availability, impacts of human activities on river flow regime alteration and agricultural land use change. The frameworks were applied to study causes and impacts of desiccation of a major lake, Lake Urmia, one of the largest saltwater lakes on Earth. This highly endangered ecosystem is on the brink of a major environmental disaster resembling that around the Aral Sea. The spatial pattern of precipitation across the Lake Urmia basin was investigated, to shed light on regional differences in water availability. Using large numbers of rainfall records and a wide array of statistical descriptors, precipitation across space and time was evaluated. Another important research component involved examining streamflow records for headwaters and lowland reaches of the Lake Urmia basin, in order to determine whether observed changes are mainly due to climate change or anthropogenic activities (e.g. water withdrawal for domestic and irrigation purposes). Principal component and clustering analyses of all available precipitation data for the lake basin revealed a heterogeneous precipitation pattern, but also permitted delineation of three homogeneous precipitation areas within the region. Further analysis identified variation in seasonal precipitation as the most important factor controlling the spatial precipitation pattern in the basin. The results showed that climate change impact on headwaters is insignificant and that irrigation is the main driving force for river flow regime alterations in the basin. This is supported by evidence that the headwaters have relatively remained unaffected by agriculture and by lack of significant changes in the historical records. The approach presented, involving clear in terpretation of existing information, can be useful in communicating land use and climate change information to decision makers and lake restoration planners
Tiivistelmä Kuivilla aridisilla ja semiaridisilla alueilla sijaitsevat kosteikot ovat hauraita ekosysteemejä. Ne ovat myös tavallista tärkeämpiä, koska ne ylläpitävät ja säätelevät ympäristön laatua sekä luonnon monimuotoisuutta. Nämä kosteikot, kuten valtaosa muistakin kosteikoista, ovat riippuvaisia vesistöalueen ylemmillä osilla tehdyistä toimista kuten vesistöjen säännöstelystä. Jopa pienet muutokset jokien virtauksissa voivat aiheuttaa merkittäviä muutoksia järvien vedenpinnan korkeuteen, suolapitoisuuteen ja tuottavuuteen. Viimeaikaiset ilmastonmuutoksen ja maankäytön muutosten aiheuttamat voimakkaat muutokset jokien virtaamiin ovat johtaneet ekosysteemien rappeutumiseen sekä monien suolajärvien kuivumiseen kuivilla ja puolikuivilla alueilla. Kuivilla alueilla sijaitsevien suolajärvien hydrologiaa ei ole tarkkailtu riittävästi niiden alhaisemman taloudellisen arvon vuoksi. Se hankaloittaa vesitaseen määrittämistä. Tarkkojen tietojen puuttuessa on vaikea arvioida myös sitä, miten vedenkäyttö ja ilmasto ovat vaikuttaneet järvien kuivumiseen. Lisäksi saatavilla olevat tiedot ovat yleensä sekä ajallisesti että alueellisesti epätarkkoja. Analysointiin tarvittavien tietojen ja välineiden puute saattaa pahimmillaan johtaa ristiriitaisiin oletuksiin. Väitöstyön päätavoite on tarjota puitteet, joilla parannetaan ymmärrystä vesivarojen alueellisista eroista, ihmisen toiminnan vaikutuksista jokien virtausten muutoksiin ja maatalouden maankäytön muutoksista käyttäen kaikkea saatavilla olevaa dataa sekä täsmentäen samalla vesistöistä jo olemassa olevaa tietoa. Väitöskirja tutkii yhden suuren järven kuivumisen syitä ja seurauksia. Urmiajärvi on yksi maapallon suurimmista suolajärvistä sekä erittäin uhanalainen ekosysteemi. Järvi on samankaltaisen ympäristökatastrofin partaalla, joka aiheutti Araljärven kuivumisen. Väitöskirja antaa tietoa veden saatavuuden alueellisista eroista tutkimalla sademäärien alueellista jakautumista Urmiajärven valuma-alueella. Tutkielmassa arvioidaan sadannan ajallista ja paikallista vaihtelua erilaisten tilastollisten menetelmien avulla. Tutkielman toinen tärkeä osa keskittyy vesialtaan latvavesistön ja tasankoalueiden valumatietoihin. Tämän osuuden päätavoite on määritellä johtuvatko havaitut muutokset järvessä pääasiassa ilmastonmuutoksesta vai ihmisen toiminnasta kuten kastelusta. Sadantatietojen pääkomponentti- ja ryhmittelyanalyysien tulokset osoittavat, että Urmiajärven allas on sadannaltaan heterogeeninen alue. Analyysi johti seudun jakamiseen kolmeen homogeeniseen sadanta-alueeseen. Analyysi osoitti, että sademäärien kausittainen vaihtelu on merkittävin järvialtaan alueellisiin sademääriin vaikuttava tekijä. Tulokset osoittavat, että ilmastonmuutoksen vaikutukset latvavesistöön eivät olleet merkittäviä ja keinokastelu on ylivoimaisesti merkittävin järvialtaan jokien virtausten muutoksiin vaikuttava tekijä. Tätä johtopäätöstä tukee se tosiseikka, että maanviljelys ei ole juurikaan vaikuttanut latvavesistöihin eikä niissä näy historiallisten lähteiden perusteella merkittäviä muutoksia. Tutkimuksen hyöty on siinä, että se tulkitsee saatavilla olevan tiedon selkeästi, joka on avuksi, kun maankäyttöön ja ilmastonmuutokseen liittyviä tietoja välitetään päättäjille ja järven kunnostusta suunnitteleville tahoille

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37

Robb, Whitney Jane. "The Effects of Laryngeal Desiccation and Nebulized Isotonic Saline in Male Speakers." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/3972.

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Hydration of the vocal folds is important for the production of normal voice. Dehydration makes voice production more difficult and increases vocal effort. Laryngeal desiccation has been shown to increase phonation threshold pressure (PTP) and self-perceived phonatory effort (PPE) in females. Nebulized saline may reverse or offset this effect. However, few data exist regarding the effects of laryngeal desiccation and nebulized treatments in males. Further, the dose-response relationship between laryngeal desiccation and nebulized hydration treatments is unknown. This study examined the effects of two doses of nebulized isotonic saline following a laryngeal desiccation challenge in healthy male speakers. In a double-blinded, within-subjects design, 10 male college students (age range 18-26 years) attended two data collection sessions involving a 30-minute desiccation challenge followed by 3 mL or 9 mL of nebulized isotonic saline. PTP for the 10th and 80th fundamental frequency (F0) percentiles and PPE were collected before and after the desiccation challenge and at 5, 35, and 65 minutes after the nebulized treatment. PPE increased significantly following the laryngeal desiccation challenge (p < .01). Following nebulization, PPE decreased toward baseline for both doses of isotonic saline (p < .01), but failed to reverse the desiccation effect completely. No statistically significant changes in PTP occurred following the laryngeal desiccation challenge or subsequent treatments. Compared with previous research involving females, these results suggest males may respond differently to laryngeal desiccation and nebulized hydration treatments.

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38

Ress, Jennifer Ann. "The Ecology of Aerial Algae." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1332874801.

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39

Pond, Sharon Elizabeth. "Improving germination in white spruce somatic embryos with desiccation and/or cold treatments." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ37359.pdf.

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40

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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42

Shen, Arthur Yen-Hsiang. "The transcriptome response of leaves of the resurrection plant, Xerophyta humilis to desiccation." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13009.

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Includes bibliographical references.
In angiosperms, desiccation tolerance, a genetic trait that enables tissues to survive loss of more than 95% of cellular water is widely observed in the seeds, but is only found in the vegetative tissues of a small group of species known as the resurrection plants. Xerophyta humilis is a small resurrection plant indigenous to Southern Africa. In this study, the hypothesis that vegetative desiccation tolerance is derived from an adaptation of seed desiccation tolerance was tested by characterizing changes in the transcriptome of X. humilis leaves during desiccation. The mRNA transcript abundance of a set of 1680 X. humilis genes was analyzed at 6 different stages of water loss in the leaves of X. humilis. Functional enrichment analysis showed that genes that were down-regulated during desiccation were over-represented with genes involved in photosynthesis, cellular developmental processes, as well as transcription regulator activity. Three distinct clusters of up-regulated genes were identified. The earliest set of up-regulated genes were enriched with genes associated with the turnover of proteins and the simultaneous synthesis of proteins required for protection. Enrichment also included genes associated with lipid body synthesis, as well as the transport of storage proteins to vacuoles. Two groups of late desiccation up-regulated genes were also identified, their expression only increased at later stages of desiccation and remained high in the desiccated leaves.

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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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Malwane, Thembeka Sebenzile Desiree. "In vitro tissue culture: Towards conservation of threatened desiccation sensitive Encephalartos cycads seeds." Master's thesis, Faculty of Science, 2019. https://hdl.handle.net/11427/31805.

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Approximately 62% of the 355 cycad species in the world are classified as threatened with extinction. The African genus, Encephalartos, has a total of 65 species, approximately 70% of which are threatened. This status emphasizes the need to conserve these species; however, the recalcitrant nature of cycads seeds makes it difficult to conserve using conventional seed banking methods. Recalcitrant seeds have a short lifespan and cannot be dried or stored for prolonged periods as they become non-viable when they lose moisture. While studies on cryopreservation for conserving cycad germplasm and banking these desiccation-sensitive seeds has made some advances, cycad conservation is still limited to ex situ living plant collections. In vitro tissue culture is a promising technique for conserving cycads. While attempts have been made, there have been few reported successes and, to date, there has been no successful regeneration of Encephalartos species. As such, this study was aimed at developing an efficient and successful in vitro regeneration protocol for two Encephalartos species. Embryo regeneration of E. altensteinii and E. manikensis was assessed, testing the effects of plant growth regulators (PGRs) - 0.5 mg/L Kinetin and 0.5 mg/L 6-BAP, alone or in combination, sucrose (0, 15 and 30 g/L) and light. Within six weeks of culture, embryos of both species were able to regenerate, however, each responded differently to the tested variables. While shoot regeneration was evident for both species during this period, this was however not explained by any of the variables assessed in this study. Rooting was highest in the treatments with 0.5 mg/L Kinetin for E. altensteinii, after subculture rooting was favoured by the treatments with 0.5 mg/L Kinetin + 0.5 mg/L 6-BAP. Encephalartos manikensis rooting was significantly higher in PGR-free treatment in the first six weeks of culture. After subculture, rooting was enhanced by the treatment with the highest PGR concentration of 1.0 mg/L Kinetin + 1.0 mg/L 6-BAP. Darkness enhanced rooting while 16h photoperiod enhanced shooting for both species. However, the regeneration of both roots and shoots was more prevalent in the treatments that were initiated in complete darkness as compared to the treatments initiated under 24h of light. Both species responded to sucrose; with increase in sucrose concentration, callus induction increased for E. altensteinii while, necrosis and contamination increased for E. manikensis. In vitro-derived E. altensteinii plantlets acclimatization was unsuccessful and only 3.5% of E. manikensis were successfully acclimatized. This study suggests that although both these species belong to the same genus, in vitro culture protocol should be species specific. The overall regeneration of both species was however low, thus the second study assessed the levels of phytohormones in E. altensteinii seed tissues (embryos and megagametophytes) of the same age as those used in the in vitro regeneration. Phytohormones, as well as multiple phytohormone interactions (i.e. interplay between Abscisic acid (ABA) and Gibberellins (GAs)), play a role in the germination, growth and development of a plant. The high levels of a germination inhibiting ABA compared to the low levels of cytokinins and auxins, as well as the absence of GAs obtained in the assessed seed tissue, suggest that no real germination was taking place. Thus these results suggest that E. altensteinii seeds have a very slow developmental process with the likely chance that at this age they may be immature.

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Bambakidis, Theodore. "Changes in Benthic Algal Community Structure Following an Unpredictable Stream-Wide Desiccation Event." Bowling Green State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1245682807.

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47

Fujiki, Robert B. "The Effects of Laryngeal Desiccation and Nebulized Isotonic Saline in Trained Male Singers." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4025.

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Vocal fold hydration is important for healthy function of the vocal mechanism. Vocal fold surface fluid protects the mucosa and facilitates efficient vocal fold oscillation. Dry air exposure, mouth breathing, insufficient intake of liquids, and behavioral factors may contribute to laryngeal dehydration. Singers are believed to be particularly at risk for voice problems related to dehydration due to environmental and voice use factors. Laryngeal desiccation and nebulized hydration treatments have been shown to influence phonation threshold pressure (PTP) and self-perceived phonatory effort (PPE) in females. However, little research exists exploring the effects of hydration in males. Additionally, few studies have examined the dose-response relationship of hydration treatments. This investigation examined the effects of a laryngeal desiccation challenge and two different doses of nebulized isotonic saline on voice production in trained male singers. In a double-blind, within-subjects repeated measures crossover investigation, 10 male singers (ages 18 to 24) received a 30 minute laryngeal desiccation challenge followed by either 3 mL or 9 mL of nebulized isotonic saline on two consecutive weeks. PTP, PPE, and self-perceived mouth and throat dryness were sampled during the following observations: predesiccation, post-desiccation, and at 5, 35, and 65 minutes post-nebulization. No differences in PTP were observed after desiccation or nebulized treatment. PPE, however, rose significantly after desiccation and returned near baseline after treatment. No significant differences between dosages were observed.

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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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Mulako, Inonge. "Characterization of the Xerophyta humilis desiccation induced-1 (Xhdsi-1voc) gene : a member of the Vicinal Oxygen Chelate (VOC) metalloenzyme superfamily upregulated in X. humilis (BAK) DUR and SCHINZ during desiccation." Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/4303.

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The resurrection plant, Xerophyta humilis is used as a model system to identify and characterise genes which play an important role in conferring desiccation tolerance in plants. In this study, the expression of a novel gene named desiccation induced-1 (dsi-1VOC) during desiccation in X. humilis and desiccationsensitive plants is characterised.

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Klage, Karsten. "Molecular analysis of the responses of Caenorhabditis elegans (Bristol N2), Panagrolaimus rigidus (AF36) and Panagrolaimus sp. (PS 1579) (Nematoda) to water stress." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28215.

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This work provides a comparative and genetic analysis of the responses to water stress in desiccation-tolerant and desiccation-sensitive nematodes. Caenorhabditis elegans, a model organism for the study of development, aging, and cell biology was shown to be a desiccation-sensitive organism that survives relative humidities above 40\% for periods of up to seven days. Transcripts from the desiccation-tolerant species Panagrolaimus rigidus AF36 and sp. PS1579, which were expressed uniquely during separate desiccation and osmotic stresses, as well as during recovery from exposure to the dual stresses, were cloned. These sequences were used to search for similarities in the genome sequence data of C. elegans. Putative anhydrobiotic-related transcripts were identified that potentially encode heat shock protein 70, late embryogenic abundant protein, and trehalose-phosphate synthase. Other putative genes that were identified within eight separate libraries encode proteins involved in transcription (histones), protein biosynthesis (ribosomal proteins, elongation factors), protein degradation (ubiquitin, proteases), and transport and cell structure (actin, collagen). Gene ontology analysis of the cloned transcripts revealed that developmental processes are activated during exposure to the stresses as well as during recovery, which may suggest a â rejuvenationâ process as a key to survival in Panagrolaimus nematodes. Genes that were up-regulated during desiccation stress in C. elegans were classified as belonging either to an early response (until 12 hours of stress), or to a late response (after 12 hours of stress). The early response was characterized by the up-regulation of a large number of genes encoding mono-oxygenases, which may suggest onset of oxidation stress during desiccation of C. elegans. The late response was characterized by the appearance of transcripts encoding proteins of the immune system, heat shock proteins (protein denaturation), and superoxide dismutases (oxidation damage). Genes in C. elegans that were down-regulated in response to desiccation stress include those encoding proteases and lysozymes (metabolic shutdown). Genes that encode channel proteins (water homeostasis) were found among the transcripts up-regulated during recovery of C. elegans. The up-regulation of gpdh-1 and hmit-1.1, two transcripts linked to hyperosmotic stress, suggest that osmotic stress is experienced by C. elegans. Comparison of these data with those obtained from exposure of C. elegans to a range of other stresses showing that the nematode C. elegans uses specific transcripts for the desiccation response; transcripts that are not induced in other stresses such as heat, anoxia or starvation. In addition, transcripts regulated during desiccation stress of C. elegans were also regulated during dauer formation, which may indicate common stress tolerant mechanisms. Recent studies in mammalian cells and C. elegans have shown that microRNAs are able to degrade and to sequester mRNA especially during stress in so called stress bodies. In this study, C. elegans microRNA knock-outs showed a significant decrease in desiccation stress survival compared to wild type C. elegans which may suggest the importance of microRNAs for stress survival in C. elegans and other organisms.
Ph. D.

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Dissertations / Theses on the topic 'Desiccation'

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