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1
Eakes, Donald Joseph. "Moisture stress conditioning, potassium nutrition, and tolerance of Salvia splendens 'Bonfire' to moisture stress". Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54350.
Testo completoAbstract (sommario):
The objective of this study was to determine the leaf water relations, gas exchange, and growth of the bedding plant salvia Salvia splendens 'Bonfire‘ as influenced by moisture stress conditioning (MSC - exposing plants to 4 sublethal dry-down cycles) and potassium (K) nutrition. Plants were fertilized with one of six K rates: 25, 75, 150, 300, 450, and 600 ppm as KCl in experiment one. Seven weeks after seeding plants were subjected to MSC. MSC and increasing K rate resulted in osmotic adjustment and increased cellular turgor potentials. Foliar K content increased as osmotic potentials decreased due to treatment. Although there was no interaction, MSC and high K rates both reduced transpiration (E), leaf conductance (g₁), and daily gravimetric water loss during well watered conditions. Greatest shoot dry weight occurred for plants grown with 300 ppm K and no-MSC.
Gas exchange of salvia as influenced by MSC during the onset of moisture stress was determined in experiment two. On day one following final irrigation, MSC plants had lower mid-day E, g₁, hourly gravimetric water loss per unit leaf area, and net photosynthesis (Pn) compared to controls, despite no differences in leaf water potential (ψ₁). Percentage of stomatal inhibition of Pn (SI) was greater for MSC plants than controls with no differences in mesophyllic resistance to CO₂ (rm). On day two, MSC plants had greater Pn, E, g₁, and hourly gravimetric water loss per unit leaf area, while SI and rm were lower than controls. MSC plants maintained positive Pn rates and turgor to lower ψ₁ than control plants. Water use efficiency (WUE) estimates for MSC plants were greater than for controls.
Salvia plants were fertilized with 75, 300, or 600 ppm K to determine the influence of K rate on gas exchange during the onset of moisture stress in a third experiment. On day one following final irrigation, plants grown with K rates of 300 and 600 ppm had lower E, g₁, hourly gravimetric water loss per unit leaf area, and Pn compared to 75 ppm K plants. On day two, 600 ppm K plants had greater Pn, E, and g₁ as the experiment was terminated compared to plants grown with 75 ppm K, although ψ₁ was similar. Potassium rate had little affect on WUE.Ph. D.
2
Le, Fevre Ruth Elizabeth. "Phytate and plant stress responses". Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708218.
Testo completo
3
Choudhury, Feroza Kaneez. "Rapid Metabolic Response of Plants Exposed to Light Stress". Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157543/.
Testo completoAbstract (sommario):
Environmental stress conditions can drastically affect plant growth and productivity. In contrast to soil moisture or salinity that can gradually change over a period of days or weeks, changes in light intensity or temperature can occur very rapidly, sometimes over the course of minutes or seconds. So, in our study we have taken an metabolomics approach to identify the rapid response of plants to light stress. In the first part we have focused on the ultrafast (0-90 sec) metabolic response of local tissues to light stress and in the second part we analyzed the metabolic response associated with rapid systemic signaling (0-12 min). Analysis of the rapid response of Arabidopsis to light stress has revealed 111 metabolites that significantly alter in their level during the first 90 sec of light stress exposure. We further show that the levels of free and total glutathione accumulate rapidly during light stress in Arabidopsis and that the accumulation of total glutathione during light stress is dependent on an increase in nitric oxide (NO) levels. We further suggest that the increase in precursors for glutathione biosynthesis could be linked to alterations in photorespiration, and that phosphoenolpyruvate could represent a major energy and carbon source for rapid metabolic responses. Taken together, our analysis could be used as an initial road map for the identification of different pathways that could be used to augment the rapid response of plants to abiotic stress. In addition, it highlights the important role of glutathione in initial stage of light stress response.
Light-induced rapid systemic signaling and systemic acquired acclimation (SAA) are thought to play an important role in the response of plants to different abiotic stresses. Although molecular and metabolic responses to light stress have been extensively studied in local leaves, and to a lesser degree in systemic leaves, very little is known about the metabolic responses that occur in the different tissues that connect the local to the systemic leaves. These could be important in defining the specificity of the systemic response as well as in supporting the propagation of different systemic signals, such as the reactive oxygen species (ROS) wave. Here we report that local application of light stress to one rosette leaf resulted in a metabolic response that encompassed local, systemic and transport tissues (tissues that connect the local and systemic tissues), demonstrating a high degree of physical and metabolic continuity between different tissues throughout the plant. We further show that the response of many of the systemically altered metabolites could be associated with the function of the ROS wave, and that the level of eight different metabolites is altered in a similar way in all tissues tested (local, systemic, and transport tissues). These compounds could define a core metabolic signature for light stress that propagates from the local to the systemic leaves. Taken together, our findings suggest that metabolic changes occurring in cells that connect the local and systemic tissues could play an important role in mediating rapid systemic signaling and systemic acquired acclimation to light stress.
4
Kalifa, Ali. "Salt stress, and phosphorus absorption by potato plants cv. 'Russet Burbank'". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq29727.pdf.
Testo completo
5
Ingarfield, Patricia Jean. "Effect of water stress and arbuscular mycorrhiza on the plant growth and antioxidant potential of Pelargonium reniforme Curtis and Pelargonium sidoides DC". Thesis, Cape Peninsula University of Technology, 2018. http://hdl.handle.net/20.500.11838/2794.
Testo completoAbstract (sommario):
Thesis (MTech (Horticulture))--Cape Peninsula University of Technology, 2018.Pelargoniums have been studied extensively for their medicinal properties. P. reniforme and P. sidoides in particular are proven to possess antimicrobial, antifungal and antibiotic abilities due to their high antioxidant potential from compounds isolated from their tuberous roots. These plants have now been added to the medicine trade market and this is now causing concern for conservationists and they are generally harvested from the wild populations. This study evaluated the effect of water stress alone and in conjunction with arbuscular mycorrhiza on two species of Pelargoniums grown in a soilless medium. The experiment consisted of five different watering regimes which were applied to one hundred plants of each species without inoculation with arbuscular mycorrhiza and to one hundred plants of each species in conjunction with inoculation with AM. All the plants in the experiment were fed with a half-strength, standard Hoagland nutrient solution at varying rates viz. once daily to pot capacity, every three days to pot capacity, every six days to pot capacity, every twelve days to pot capacity and every twenty-four days to pot capacity. The objectives of the study were to measure the nutrient uptake, SPAD-502 levels (chlorophyll production) and metabolite (phenolics) formation of both species, grown under various rates of irrigation and water stress, as well with or without the addition of arbuscular mycorrhiza at planting out. Each treatment consisted of 10 replicates. SPAD-502 levels were measured weekly using a hand held SPAD-502 meter. Determination of nutrient uptake of macronutrients N, K, P, Ca, Mg and Na and micronutrients Cu, Zn, Mn, Al and B were measured from dry plant material at the end of the experiment by Bemlab, 16 Van Der Berg Crescent, Gants Centre, Strand. Plant growth in terms of wet and dry shoot and root weight were measured after harvest. Determination of concentrations of secondary metabolites (phenolic compounds) were assayed and measured spectrophotometrically at the end of the experiment. The highest significant reading of wet shoot weight for P. reniforme was taken in treatments 1 and 2 with and without mycorrhiza i.e. WF1, WF1M, WF2 and WF2M, with the highest mean found in WF1 with no mycorrhiza. This indicates that under high irrigation AM plays no part in plant growth, possibly due to leaching. More research is necessary in this regard. With regard to wet root weight, this was found to be not significant in any of the treatments, other than the longest roots being found in WF4. Measurements for dry root weight showed that WF1,2,3 and 5 were the most significant at P≤ 0.001 significance, with the highest weight found at treatment being WF3 and WF3M. The highest mean of shoot length of the plants was measured in treatment WF2 at moderate watering, but no statistical difference was found with water application and mycorrhiza addition. Nutrient uptake was increased in P. sidoides in all the different watering levels in the experiment except in the uptake of Mg. AM inoculation showed an increase in the uptake of Ca, while absorption of N occurred at higher water availability. K uptake was enhanced by the addition of AM in high water availability and K utilisation decreased as water stress increased. Medium to low watering resulted in higher leaf content in P. sidoides while the interaction between water availability and AM inoculation increased chlorophyll production towards the end of the experiment.
6
Zhou, Maoqian 1961. "Nitrogen fixation by alfalfa as affected by salt stress and nitrogen levels". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277231.
Testo completoAbstract (sommario):
The growth and Nitrogen fixation by one low salt tolerant alfalfa (Medicago sativa L.) and two germination salt tolerant selections inoculated with were investigated at two salt levels (0, -0.6 Mpa) and two N rates (1, 5ppm) using a system which automatically recirculates a nutrient solution. The high level of salinity (-0.6 Mpa osmotic potential of culture solution) resulted in substantial reduction in the N fixation percentage and total fixed N. The effect of salinity was more pronounced for later cuttings than for the earlier cutting. The N fixation percentages were substantially decreased by increasing N level and the reduction was enhanced by time. The N treatment levels did not exhibit a significant effect on total fixed N. Cultivars did not differ in either growth or N fixation. However, the interaction of N and salinity significantly decreased the percentage and amount of N fixation.
7
Zegeer, Abreeza May 1956. "Interactions between saline stress and benzyladenine on chili peppers (Capsicum annuum L.)". Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277069.
Testo completoAbstract (sommario):
Exogenous application of BA (0, 50, 100 mg ul--1) had no significant effects on tolerance of chili peppers to salt (--0.75 MPa NaCl:CaCl₂, 3:1, w/w) as measured by vegetative and reproductive weights, numbers of reproductive structures, transpiration and total chlorophyll. When peppers were applied with microliter amounts of ¹⁴C labelled benzyladenine (BA; 44,400 dpm 1⁻¹), BA was translocated primarily acropetally from the site of application. Regardless of application site, translocated BA was ported primarily to expanding leaves, and BA was more readily absorbed by leaf as opposed to stem surfaces. Exogenous application of BA (0, 50, 100 mg ul⁻¹) had no significant effects on tolerance of chili peppers to salt (-0.75 MPa NaCl:CaCl₂, 3:1, w/w) as measured by vegetative and reproductive weights, numbers of reproductive structures, transpiration and total chlorophyll.
8
Wongareonwanakij, Sathaporn. "Effects of water stress and partial soil-drying on senescence of sunflower plants". Title page, contents and summary only, 1995. http://web4.library.adelaide.edu.au/theses/09A/09aw872.pdf.
Testo completoAbstract (sommario):
Bibliography: leaves 98-123. This thesis investigates the symptoms of leaf senescence in response to plant shoot water stress and demonstrates the effect of a non-hydraulic root signal in the senescence response of mature leaves of sunflower. The alleviation of the leaf soluble protein loss rate by excision of the root system in drying soil indicates that this signal originates in roots in dry soil and acts to promote protein loss.
9
Attumi, Al-Arbe. "Effect of salt stress on phosphorus and sodium absorptions by soybean plants". Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20242.
Testo completoAbstract (sommario):
The radiotracer methodology was combined with the Hoagland solution culture of growing soybean in a greenhouse to investigate the absorptions of phosphorus (P), calcium (Ca), and sodium (Na) as a function of salinity. Salt stress was varied by using zero to 120 mM NaCl. The research was initiated because of a need to increase soybean production in the saline soils of the semi-arid regions of the world. Although P absorption increased with time at each concentration of NaCl, increasing its concentrations ([NaCl]) to 120 mM reduced P uptake considerably. The addition of inorganic P (Pi) to the salt medium improved P absorption significantly (P < 0.0001) in stem, petiole, and roots. Polynomial regressions showed the relationship between 22Na activity and [NaCl] for leaves and petiole to be cubic (R2 = 1) while in the stem a quadratic relationship prevailed. A maximum of P and Na absorption was observed at 40 mM NaCl. The relationship between 32P activity and increasing [NaCl] was linear for the roots (a positive slope) and the stem (a negative slope). 45Ca and 32P dual labelling part of the experiments failed to produce results because an unexpectedly high degree of tissue quenching which prevented from obtaining the minimum counting requirements for separation. Shoot fresh and dry weights decreased linearly with increasing [NaCl] as did the root fresh and dry weights. Leaf chlorophyll content during the last week of the final harvest showed a linear relationship with time. Chlorophyll increased with time linearly when the growth medium contained zero and 40 mM NaCl; whereas a negative slope was obtained for 80 and 120 mM NaCl. It seems that P fertilization of the soil could ameliorate the salt effect. 22 Na uptake results indicated that there is a mechanism for exclusion of Na from soybean plant parts.
10
Maclear, Athlee. "Identification of cis-elements and transacting factors involved in the abiotic stress responses of plants". Thesis, Rhodes University, 2005. http://hdl.handle.net/10962/d1007236.
Testo completoAbstract (sommario):
Many stress situations limit plant growth, resulting in crop production difficulties. Population growth, limited availability and over-utilization of arable land, and intolerant crop species have resulted in tremendous strain being placed on agriculturalists to produce enough to sustain the world's population. An understanding of the principles involved in plant resistance to environmental stress will enable scientists to harness these mechanisms to create stress-tolerant crop species, thus increasing crop production, and enabling the farming of previously unproductive land. This research project uses computational and bioinformatics techniques to explore the promoter regions of genes, encoding proteins that are up- or down-regulated in response to specific abiotic stresses, with the aim of identifying common patterns in the cis-elements governing the regulation of these abiotic stress responsive genes. An initial dataset of fifty known genes encoding for proteins reported to be up- or down-regulated in response to plant stresses that result in water-deficit at the cellular level viz. drought, low temperature, and salinity, were identified, and a postgreSQL database created to store relevant information pertaining to these genes and the proteins encoded by them. The genomic DNA was obtained where possible, and the promoter and intron regions identified. The Neural Network Promoter Prediction (NNPP) software package was used to predict the transcription start signal (TSS) and the promoter searching software tool, TESS (Transcription Element Search Software) used to identify known and user-defined cis-elements within the promoter regions of these genes. Currently available promoter prediction software analysis tools are reported to predict one promoter per kilobase of DNA, whilst functional promoters are thought to only occur one in 30-40 kilobases, which indicates that a large perccntage of predictions are likely to be false positives (pedersen et. al., 1999). NNPP was chosen as it was rated as the highest performing promoter prediction software tool by Fickett and Hatzigeorgiou (1997) in a thorough review of eukaryotic promoter prediction algorithms, however results were less than promising as very few predicted TSS were identified in the area 50 bps up- and downstream of the gene start site, where biologically functional TSSs are known to occur (Reese, 2000; Fickett and Hatzigeorgiou, 1997). TESS results seemed to support the hypothesis that drought, low-temperature and high salinity plant stress response proteins have similar as-elements in their promoter regions, and suggested links to various other gene regulation mechanisms viz. gibberellin-, light-, auxin- and development-regulated gene expression, highlighting the vast complexity of plant stress response processes. Although far from conclusive, results provide a valuable basis for future comparative promoter studies that will attempt to deduce possible common transcriptional initiation of abiotic stress response genes.KMBT_363
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11
Alm, David Michael. "Comparison and interaction of heat and salt stress in cultured tobacco cells". Virtual Press, 1986. http://liblink.bsu.edu/uhtbin/catkey/445616.
Testo completoAbstract (sommario):
Cultured tobacco cells (Nicotiana tabacum L., cv Wisconsin-38) were subjected to temporary sub-lethal heat and salt shock treatments to determine the effects of these treatments on various physiological parameters after subsequent lethal heat or salt stresses. Tobacco cells developed a tolerance to a non-permissive temperature stress (54C for 14 min) when pretreated with heat shock of 38C for 2h but not when pretreated at 42C for 2h. Cells pretreated at 38 (2h) exhibited less than 30% normal growth when the 54C stress came immediately after the 38C treatment. Tolerance to the 54C stress developed with increased interval between shock and stress with cells exhibiting 95% normal regrowth when the 54C stress was administered 8h after the 38C shock. The developement of heat tolerance was inhibited if heat shock was done in the presence of a non-injuring level of EGTA (.0.5mM). Cells treated with EGTA during heat shock grew normally at 23C but not after a 54C heat stress. EDTA (0.5mM) had little effect on the acquisition of tolerance to heat stress.Wisconsin-38 cells developed a tolerance to a non-permissive salt stress (2% NaCl for 16h) when pretreated at a lower salt level (1.2% NaCl) for 3h. Cells heat shocked at 38C exhibited increased tolerance of the lethal salt stress up to 8h. Conversely, cells heat shocked at 42C exhibited immediate tolerance to lethal salt stress and this tolerance decayed over eight hours. The heat shock-induced acquisition of salt tolerance was inhibited by both EGTA and EDTA.Proteins synthesized during heat and salt stress treatments were labeled with [35S]-methionine and/or [3H]-leucine and separated using Sodium dodecylsulfate polyacrylamide gel electrophoresis. Fluorographic analysis of the gels indicate that a number of proteins are produced in response to heat shock. Similar analysis of proteins from salt shocked cells indicates that no salt shock proteins are produced in response to a brief low-level sodium chloride shock.
12
Leblanc, Rosanne. "Protein synthesis and drought stress in two rapeseed cultivars". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60487.
Testo completoAbstract (sommario):
Desiccation effects on rate and pattern of protein synthesis in Brassica napus (cv westar) and Brassica juncea (cv cutlass) have been examined. Results showed that while the rate of water loss was similar in the two species, the inhibition of amino acid incorporation was greater in B. napus than B. juncea at any given level of desiccation. Electrolyte leakage increased with the degree of desiccation and was greater in B. napus than in B. juncea. In both, the increase in leakage was much sharper after 12 hours of desiccation. Quantitative changes in patterns of boiling-stable protein synthesis due to desiccation stress were observed. The control level of protein radioactivity which was boiling-stable in B. napus was 16.16% and 19.96% for B. juncea. After desiccation, the percentage of boiling-stable radioactivity increased to 23.30% for B. juncea and 16.63% for B. napus. In vitro translation of total RNA indicated that desiccation alone does not induce the synthesis of new mRNA species in either cultivar, but it may change the translation pattern resulting in different levels of abundance of proteins.
13
Phillips, Trevor David. "Stress manipulation in Dunaliella salina and dual-stage [beta]-carotene production". Thesis, Rhodes University, 1994. http://hdl.handle.net/10962/d1004097.
Testo completoAbstract (sommario):
The alga Dunaliella salina accumulates large quantities of β-carotene in response to certain environmental and physiological stresses. This hyper-accumulation process has been commercially exploited. However, the currently employed averaging or single-stage process produces β-carotene yields well below the genetic potential of the organism due to the inverse relationship between growth and secondary metabolite production. A dual-stage process, which separates the distinctive growth and secondary metabolite production stages of the alga, has been proposed. The broad aim of the research programme was to evaluate the practicality, scale-up and economic viability of a dual-stage β-carotene production process from D. salina. Preliminary laboratory studies showed that although stress factors such as high salinity and a range of nutrient limitations enhance β-carotene accumulation in D. salina, high light intensity is the single most important factor inducing β-carotene hyper-accumulation in the alga. Furthermore, the preliminary studies indicated that 6-carotene production could be successfully manipulated by the imposition of stress. The stress response of D. salina to high light stress was examined at a fundamental level. The relative partitioning of β-carotene between thylakoid membrane and interthylakoid globular β-carotene has revealed two responses to high light stress. The first is a response in which the alga adapts to the photoinhibitory effects of high light stress by the rapid accumulation and the peripheral localisation of Jl-carotene to the outer extremities of the chloroplast. This is followed by a maintenance response which is characterised by the recovery of the photosynthetic rate and cell growth. A possible interrelationship between the extent of the photo inhibitory response and the amount of β-carotene hyper-accumulation has been noted. An outdoor evaluation of the growth stage of the dual-stage system has demonstrated that D. salina can be grown in a relatively low salinity, nutrient sufficient medium for extended periods without overgrowth by small non-carotenogenic Dunaliella species. In addition, biomass productivities of three times greater than those obtained in the currently employed averaging system were achieved. The role of high light intensity in β-carotene hyper-accumulation was confirmed in outdoor scale-up stress pond studies. The studies demonstrated the feasibility of stress induced ll-carotene production in outdoor cultures of D. salina and β-carotene yields three times greater than those obtained in the currently employed averaging process were achieved. The dual-stage process imposes the specific requirement of viable cell separation on the harvesting system employed. A flocculation-flotation process and an air-displacement crossflow ultrafiltration system were developed and successfully evaluated for the separation of D. salina from the brine solution in a viable form. The extraction of β-carotene from D. salina was evaluated. Supercritical fluid extraction studies showed that the use of a co-solvent mixture of carbon dioxide and propane could effectively reduce the high extraction pressures associated with supercritical carbon dioxide extraction. In addition, a novel hydrophobic membrane assisted hot oil extraction process was developed which separates the complex oil-water emulsions produced during hot oil extraction of 6-carotene from wet D. salina biomass. Process design and economic evaluation studies were undertaken and showed that the economics of the dual-stage process offer significant advantages over the currently employed averaging process.
14
Louw, Cassandra Alexandrovna. "Wheat stress responses during Russian wheat aphid and Bird Cherry Oat aphid infestation : an analysis of differential protein regulation during plant biotic stress responses /". Thesis, Rhodes University, 2007. http://eprints.ru.ac.za/834/.
Testo completo
15
Phillips, Lesley Gail. "Constituent processes contributing to stress induced β-carotene accumulation in Dunaliella salina". Thesis, Rhodes University, 1995. http://hdl.handle.net/10962/d1005341.
Testo completoAbstract (sommario):
The alga Dunaliella salina possesses the unique ability to accumulate up to 14 % of it's dry weight as β-carotene in response to stress conditions. This hyper-accumulation of β-carotene has led to the commercial exploitation of this alga for the biotechnological production of this important carotenoid. In order to maximise β-carotene production, a dual-stage process which separates the distinctive growth phase from the β-carotene accumulating stress phase has recently been patented. Preliminary laboratory studies showed that although stress factors such as high salinity and nutrient limitation enhance β-carotene accumulation in D. salina (± 10 pg.cell⁻¹), high light intensity was the single most important factor contributing to the induction of β-carotene accumulation in this alga (± 20 pg.cell⁻¹). Moreover, it was demonstrated that β-carotene accumulation can be further stimulated by exposing the alga to a combination of high light intensity, salt and nutrient stresses (± 30-60 pg.cell⁻¹). The response of D. salina to stress was shown to occur in two phases. The first phase occurred within 24 hours and was characterized most importantly by higher rates of β-carotene accumulation for all the stresses investigated. In cells exposed to multiple stress factors in mass culture, the β-carotene accumulation rate was as much as 9.5 pg.cell⁻¹.day⁻¹ in the first phase compared to only 3 pg.cell·day⁻¹ in the second phase. Since the rate of β-carotene accumulation was higher within the first 24 hours after exposure to stress, the first phase was considered crucial for stress-induced β-carotene accumulation. Characterization of this phase revealed that the stress response was multifaceted. Transition of cells from the growth stage to stress conditions was characterized by the following: 1) Change in cell volume. Hypersalinity caused cell shrinkage while cells exposed to nutrient limitation and/or high light intensity caused cells to swell. Restoration of cell volume was shown to occur within 8 hours for all stresses investigated. 2) Altered photosynthesis. Inhibition of both carbon fixation and oxygen evolution was demonstrated in cells immediately after exposure to multiple stress factors. 3) Production of abscisic acid. Intracellular ABA levels increased within 6-8 hours after exposure to all stresses investigated. The rise in intracellular ABA levels coincided with an increase or return to starting cell volume. High intracellular ABA levels were however transient and within 24 hours ABA began to partition into the culture medium. 4) Change in pigment composition. Changes in xanthophyll cycle pigment content was demonstrated soon after exposure to stress conditions. In hypersalinity shocked cells, initial epoxidation of zeaxanthin to violaxanthin and subsequent de-epoxidation to zeaxanthin occurred, whereas exposure to high stress resulted in an immediate and continued decrease in the epoxidation state indicating accumulation of zeaxanthin. A rapid rate of chlorophyll depletion was also demonstrated. In addition to the above responses a rapid decrease in growth rate during this phase was also noted. An interrelationship between cell volume change, ABA production, maintenance of xanthophyll cycle operation and β-carotene accumulation therefore appeared to exist. ABA production was shown to be stoichiometrically related to changes in xanthophyll content with r² = 0.84 and slope of the curve = 0.91 being achieved for high light stressed cells. This study therefore presents strong circumstantial evidence in support of a carotenoid origin for ABA in Dunaliella. In addition, enhanced β-carotene content was achieved by the application of exogenous ABA and related compounds suggesting a role for ABA as a regulator of the overall stress response. Furthermore, zeaxanthin accumulation was shown to be positively correlated ( r²≥ 0.81) to β-carotene accumulation for all the stresses investigated. The second phase was characterized by a return to homoeostasis of the physiological processes mentioned above, indicating acclimation of the cell to prevailing conditions. This stage was characterised by continued β-carotene accumulation and a decreased epoxidation state of the xanthophyll cycle which together appeared to sustain photosynthesis, allowing this organism to tolerate stress conditions.
16
Kathiria, Palak, e University of Lethbridge Faculty of Arts and Science. "Transgenerational changes in progeny of compatible pathogen infected plants". Thesis, Lethbridge, Alta. : University of Lethbridge, Dept. of Biological Sciences, 2010, 2010. http://hdl.handle.net/10133/2588.
Testo completo
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Larsson, Marie-France. "The Effect of Plants on Individuals' Stress Level in an Indoor Work Environment". Thesis, Mid Sweden University, Department of Social Sciences, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-11141.
Testo completoAbstract (sommario):
Many instances of sick leave can be linked to diseases caused by stress. An efficient way to counter the negative effects of stress is coping. However, trying to fit coping activities into an already busy schedule can be stressful in itself. Therefore it is interesting to study passive stress-reducing methods, for instance interaction with nature. This paper studied the effect of the presence of plants in a work-like environment on the stress level of 30 participants divided equally in a control group and a test group by measuring their heart rate. A factorial analysis of variance and a multivariate analysis of variance were used to analyze the data. Despite the heart rate of the control group being on an average 5 beats per minute higher than the test group, the difference was found not to be statistically significant. An explanation for this could be the poor reliability of heart rate as a measure of stress.
Keywords: coping, heart rate, indoors, nature, plants, stress, work
18
Bilichak, Andriy. "The role of epigenetics in the maintenance of plant genome stability". Thesis, Lethbridge, Alta. : University of Lethbridge, Dept. of Biological Sciences, 2013. http://hdl.handle.net/10133/3448.
Testo completoAbstract (sommario):
Significant alterations in the environmental conditions can have pronounced
effects on plant genome stability. Recent evidence argues for a global involvement of the
components of epigenetic modules in the regulation of genome homeostasis both
immediately after stress exposure and long after environmental cues were acquired. The
last observation is of particular interest as the memory of imposing stress can be
maintained at the molecular level throughout plant ontogenesis and may be faithfully
propagated into the following generation. Our study provides evidence that epigenetic
repercussions exerted by stress exposure of parental plants manifest themselves in
untreated progeny at all three levels of the epigenetic module: DNA methylation, histone
posttranslational modifications and small RNA metabolism. Additionally, the results of
our study shed new light on the engagement of the epigenetic machinery in the
maintenance of plant genome integrity by counteracting the activity of invading nucleic
acids.xv, 280 leaves : ill. ; 29 cm
19
Rasmussen, Scott Lynn 1958. "The effects of salinity stress on the development of Pythium blight of Agrostis palustris". Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/276627.
Testo completoAbstract (sommario):
Salinity stress predisposed Penncross creeping bentgrass to cottony blight caused by P. aphanidermatum. Studies were conducted on the effects of salinity on the mycelial growth of P. aphanidermatum and on the growth of Penncross bentgrass. Mycelial growth increased significantly up to Ec levels of 7.1 ds/m when compared to mycelial growth at the control Ec levels of 0.5 ds/m. Plant growth was reduced to 50% of the control at Ec levels of 4.3 ds/m. 3-month-old Penncross bentgrass plants were inoculated and incubated at two differing temperatures. At 32 C, all plants died within 3 days regardless of salinity treatment. Rates of plant death were greatest at salinity levels over 2.8 ds/m. At 27 C, plants irrigated with water at Ec levels from 4.3 to 7.1 ds/m showed complete necrosis within 5 days, while treatments irrigated with tap water showed no disease symptoms.
20
Sumardi, of Western Sydney Hawkesbury University, of Agriculture Horticulture and Social Ecology Faculty e School of Horticulture. "The influence of water stress on flowering and fruit production of Capsicum annuum Longum (chilli peppers)". THESIS_FAHSE_HOR_Sumardi_X.xml, 1993. http://handle.uws.edu.au:8081/1959.7/82.
Testo completoAbstract (sommario):
Severe water stress reduced the number of flowers produced by Capsicum annuum var. annuum L. Longum plants, but the timing of flower production was less affected. The use of different plant establishment techniques modified flower production. Bare rooted transplants slowed the rate of flower production in comparison with direct seeded plants or those established from cell tray transplants. Bare rooted transplants delayed the onset of water stress. The capabilities of male and female gametophytes were reduced by water stress, with the female more affected, and the interaction of male and female gametophytes was affected by moderate water stress. Moderate water stress increased the time to fruit set, but affected neither the number nor percentage of fruit set, whereas severe water stress increased the time and reduced the number and percentage. Severe water stress reduced the number and percentage of mature fruit, fruit quality indices and total fruit yield. Moderate water stress reduced the number of seeds per fruit and fruit dry weight, but total fresh weight yield was not significantly affected. The time to fruit set was negatively correlated with the quality indices of mature fruit, whereas the number of seeds was positively correlated with the same. Fertilisation determined the success of seed set, and the rapidity of fruit set. Successful fertilisation can only occur when the pollen tube arrives at a viable ovule. The processes of pollen tube growth and longevity of the ovule are the factors most critically affected by water stress in determining the yield of C. annuum Longum.Master of Science (Hons)
21
Migicovsky, Zoë. "Transgenerational inheritance of epigenetic response to abiotic stress in Arabidopsis thaliana". Thesis, Lethbridge, Alta. : University of Lethbridge, Dept. of Biological Sciences, c2012, 2012. http://hdl.handle.net/10133/3311.
Testo completoAbstract (sommario):
Abiotic stresses are one of the major limiting factors of plant growth and thus
crop productivity. Exposure to these stresses, including temperature and UV, cause
physiological and epigenetic changes in plants. Such changes may be inherited in the
progeny of stressed plants, and may change their ability to respond to stress. To
understand the ability of plants to inherit an epigenetic stress memory as well as the
physiological manifestations of such a memory, we propagated both stressed and control
plants and compared the progeny under both normal and stressed conditions. In addition
to wild-type plants we used Dicer-like mutants dcl2, dcl3 and dcl4, as Dicers have been
linked to RNA-directed DNA methylation, a form of epigenetic memory. These studies
revealed that leaf number decreases in the progeny of stressed plants, and bolting occurs
earlier in the progeny of temperature stressed plants but later in the progeny of UV-C
stressed plants. Transposons were also re-activated in the progeny of stressed plants.
While heat shock transcription factor 2A increased expression in the progeny of heat
stressed plants, many genes involved in DNA repair and histone modifications decreased.
DCL2 and DCL3 appeared to be more important in transgenerational stress memory than
DCL4. However, all dcl plants were generally not significantly different than wild-type
plants, indicating that a single DCL deficiency may be compensated for by another DCL.xiv, 246 leaves : ill. ; 29 cm
22
Korban, Martine. "The effects of mechanically induced stress on in vivo and in vitro roses /". Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61238.
Testo completoAbstract (sommario):
Protocols for the successful micropropagation of 'Queen Elizabeth' ('Q.E.') and 'Dick Koster' ('D.K.') roses were established, yielding a seven-ten fold multiplication rate per month. The effects of mechanically induced stress (MIS) (shaking stress) were evaluated on early establishment of greenhouse-grown 'Q.E.' and 'D.K.' rose cuttings and the ex vitro survival and hardiness of micropropagated 'Q.E.' plantlets. Shaking 'Q.E.' rose cuttings at 200 rpm for 30 min daily for 4 weeks during the rooting stage increased root length, dry weight and the root:shoot dry weight ratio. Similar shaking of 'D.K.' rose at 200 rpm for 15 min increased shoot fresh and dry weight and root length and dry weight. Prior to ex vitro acclimatization, plantlets shaken at 150 rpm for 15 min had reduced leaf dry weights. Those shaken at 200 rpm for 15 min had lower specific root water content but greater percent root dry matter. MIS was not directly implicated in improving ex vitro survival and hardiness of 'Q.E.' rose. (Abstract shortened by UMI.)
23
Lawson, Inez Ilicia. "Invertebrate Community Composition Across Inundation Regimes and Its Potential to Reduce Plant Stress". PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3891.
Testo completoAbstract (sommario):
Appreciation of the ecological and economic values associated with healthy salt marshes has led to a recent rise in the number of marshes that are being targeted for restoration by dike removal. The success of restoration is often measured by the return of marsh plants, though this overlooks a key component of salt marshes, that of the invertebrate community within marsh sediments. To evaluate the short-term recovery of these invertebrates, sediment cores were collected across an elevational gradient in a recent dike removal marsh, one and two years post removal, and a nearby reference marsh. Abundance, richness and diversity as well as morphospecies community composition were compared across treatment groups (Reference, Removal) and elevation zone (High Marsh, Low Marsh). Morphospecies richness, abundance and diversity were significantly higher in Low Marsh samples than in High Marsh samples, though no statistically significant differences were found across treatments of the same elevation (e.g., Reference Low Marsh versus Removal Low Marsh). Pair-wise ANOSIM results found significant differences between community compositions across treatments, specifically Reference Low Marsh and Removal Low Marsh.
The marsh edge, the lowest point of vascular plant growth before transitioning to tide flats, is considered a high stress environment for emergent vegetation. Plant establishment and survival in this low elevation zone is limited by the tolerance to inundation duration and frequency and anoxic sediments. Bioturbation and burrowing by macroinvertebrates increases the surface area exposed to surface water for gas exchange, increasing the depth of the redox potential discontinuity layer. Crabs that make stable, maintained burrows have been shown to increase oxygen penetration into sediment, improving plant productivity. Such crabs are not found in salt marshes of the Pacific Northwest of North America. However, other burrowing invertebrates may have a positive impact on plant health in these areas by reducing abiotic stress due to anoxic sediments, thereby allowing plants to establish and survive lower in the intertidal zone. To assess this potential relationship, study plots of Distichlis spicata were selected at equivalent elevations at the lowest point of plant establishment at the marsh edge. Focal plant rhizomes were severed from upland ramets and assigned an invertebrate abundance treatment based on a visual burrow count surrounding each plant (9 cm diameter). Focal plants were visited monthly from July to September 2016, plant health variables of chlorophyll content and chlorophyll fluorescence (photosynthetic efficiency), and sediment ORP readings were collected. Plant survivorship was significantly higher in plots with invertebrates, 96% of plants in 'With Invertebrate' plots and 50% of plants in 'No Invertebrates' plots survived the duration of the study. Plant health (chlorophyll content and chlorophyll fluorescence) generally increased with increased invertebrate presence though, not statistically significant. There may be potential for improved plant productivity and resilience to plants at the marsh edge due to invertebrate burrowing activity. This benefit could help mitigate projected losses in plant productivity due to sea level rise, though more research is needed to investigate the mechanism by which these invertebrates confer a health benefit to plants at the marsh edge.
24
Li, Yimin. "Redox control of the transcriptional response to oxidative stress by Arabidopsis redox-sensitive basic leucine zipper protein 68". HKBU Institutional Repository, 2016. https://repository.hkbu.edu.hk/etd_oa/324.
Testo completoAbstract (sommario):
Cellular redox states mediate various physiological and developmental processes. Mechanisms involved in sensing cellular redox state and linking it to an appropriate physiological response remains poorly understood in plants. Arabidopsis bZIP68 was previously found to undergo reversible oxidation in its Cys320 in cells under oxidative stress. In this study, it was found that bZIP68 was localized in the nucleus in Arabidopsis seedlings under normal conditions. Upon treatment of oxidative stress, bZIP68 underwent nucleocytoplasmic shuttling and accumulated in the cytoplasm. This stress-dependent nucleocytoplasmic shuttling depends on the redox-sensitive Cys320 and its nuclear export signal. bZIP68 suppresses expression of stress response genes under normal conditions and its loss-of-function mutation of bZIP68 leads to elevated expression of genes involved in oxidative stress defense including genes encoding for antioxidant proteins and for enzymes involved in biosynthesis of small molecule antioxidants. The bzip68 mutant also showed enhanced responses to stress treatment such as the oxidative stress and cold stress. Our study suggests that bZIP68 directly or indirectly senses perturbation of cellular redox states and links the redox change to activation of oxidative stress defense genes through redox regulation of transcription.
25
Richards, Siân Louise. "The involvement of Arabidopsis thaliana Annexin 1 in abiotic stress response pathways". Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648626.
Testo completo
26
Reed, Mickey Lynn 1952. "The effect of moisture stress and salinity on germination and growth of grain amaranth Amaranthus cruentus L and Amaranthus hypochondriacus L". Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276777.
Testo completoAbstract (sommario):
The grain amaranths, Amaranthus cruentus and Amaranthus hypochondriacus have been promoted as grain-bearing plants of possible high productivity in saline or hot arid habitats. To investigate these claims, seeds of both species were germinated at 10, 15, 20, 25, 30, 35 and 40°centigrade. Germination percentage for both species was above 90% after four days at 20, 25, 30, and 35°C. Germination was negligible at 10 and 15°C and very low at 40°C. Seeds were germinated in isotonic solutions of PEG and NaCl at 0.0, -0.2, -0.4, -0.5, -0.6, -0.8, and -1.0 MPa osmotic potential at 30°C. Germination percentage was high in the range 0.0 to -0.4 MPa and dropped rapidly to zero in the -0.6 to -1.0 MPa range. Differences due to chemical effects were significant. Species differences were not. Radicles and hypocotyls were measured after six days in the above media. PEG was more inhibitory of seedling growth than was NaCl and generally inhibited A. cruentus more than A. hypochondriacus. This was also true of NaCl. All growth functions were slightly inhibited at 0.0 to -0.4 MPa and very inhibited above -0.6 MPa. PEG radically increased root/shoot ratio in both species.
27
Ncise, Wanga. "Environmental stress effects on the phytochemistry and bioactivity responses of a South African medicinal bulbous plant, Tulbaghia violacea Harvey (Alliaceae)". Thesis, Cape Peninsula University of Technology, 2018. http://hdl.handle.net/20.500.11838/2854.
Testo completoAbstract (sommario):
Thesis (MTech (Horticulture))--Cape Peninsula University of Technology, 2018.Deteriorating living and environmental conditions have contributed to the increasing prevalence of diseases in plants and animals. In humans, accumulation of abnormally high levels of free radicals in the tissues has been implicated in many non-communicable diseases, such as diabetes, cancer, arthritis, ischemia, gastritis, obesity and asthma. Worldwide, there is recognition of need to improve plant and animal health. Tulbaghia violacea (Alliaceae) is a medicinal plant that is extensively harvested by traditional healers in the wild for its medicinal uses and if this practice continues, it may result in an unsolicited decline of the species in situ. Therefore, there is a need for cultivation of this species. Plant cultivation in a controlled environment for conservation purposes as well as the enhancement of yield and quality is gaining favour among farmers and consumers. The main aim of this study was to investigate the effects of altering the growing conditions by applying environmental stresses on the plant growth, antifungal and antioxidant activities of T. violacea, with the view of enhancing the future cultivation of this species for pharmaceutical companies, traditional healers and the horticulture industry. This study was divided into two parts, and the first part, which was further sub-divided into two separate preliminary experiments, is presented in chapter three. Simultaneous assessments of the effects of i) varied pH levels (pH 4, pH 6, pH 8) and ii) light intensity on plant growth, antioxidant-content and -capacity of extracts of T. violacea were carried out. The second part of the thesis consisted of a more detailed assessment of the above-mentioned independent variables and interactions thereof on plant growth, and antifungal activity of extracts of T. violacea. Results obtained from the first part of the study, showed that plants exposed to pH 6 showed a marked increase in plant height (from 25-37 cm) after 2 months of treatment although, generally, the variations of the different growth parameters among the pH treatments were not significant (p > 0.05). Antioxidant-contents and -capacity were not significantly different (p > 0.05) when pH treatments were compared. However, a high polyphenol content value (of 3 mg/g) occurred in leaves of plants exposed to pH 8. Overall, comparatively, there was no significant difference (p > 0.05) in antioxidant-content and -capacity when pH treatments. In the light experiment, decreasing light intensity led to the elongation of plant height. A higher mean shoot length of 34.6 cm was obtained under low light compared to normal light (26.5 cm) two months post-treatment. The results obtained in this study indicated that light had a significant affect (p < 0.05) on the vegetative growth of this species. In contrast, normal light intensity yielded higher antioxidant-content and -capacity. The polyphenol and flavanol content were fluctuating between the averages of 5.8 mg/g to 8.5 mg/g. Overall, there was a significant difference (p < 0.05) in the antioxidant-content and -capacity when low and normal light intensity treatments compared. In conclusion, both normal light intensity and at pH 8 induced better antioxidant results. In the second part of the study, chapter four, one-month old T. violacea plantlets were grown under two light intensities (low light and normal light) in a greenhouse and concurrently exposed to varying pH levels: pH 4, pH 6 and pH 8. Plants exposed to normal light received natural sunlight through the roof of the greenhouse, while low light intensity (40% reduction) was achieved using shade nets. Plants were drip irrigated with Nutrifeed fertilizer. Plant growth parameters such as height and fresh and dry weights were determined. Leaf samples were analysed for macro-and micro-nutrients contents. Antifungal tests were carried out on the plant extracts from the various treatments in an antifungal bioassay (minimum inhibitory concentration [MIC]). The experimental data collected were analysed using one and two-way analyses of variance (ANOVA), and Tukey HSD was used to separate the means at p < 0.05 level of significance. Varied effects of different pH levels (4, 6 and 8) and light intensities (low and normal) on plant height, and fresh and dry weights were recorded in the current study. A significant interactive (df, 2; F = 0.001; p < 0.001) effect between pH and light on fresh weight was observed. The results revealed that there was a significant difference (df, 2, 57; F = 12.63; p < 0.001) in dry weights with plants under normal light intensity and pH 4 treatment (8.285 ± 0.802 g) producing the highest dry weight. There was a significant interaction (df, 2; F = 6.4; p < 0.001) between pH and light intensity on plant dry weight. Extracts from plants grown under normal light intensity showed stronger antifungal activity at pH level 4, and MIC values ranged from 0.18 ± 0 to 0.375 ± 0.04 mg/ml at 6h and 1.5 ± 0 to 0.97 ± 0.18 mg/ml at 18h. In conclusion, this study demonstrated the interactive effects of pH and light intensity on the growth of T. violacea. These findings also confirmed that it is possible to enhance the cultivation of T. violacea under greenhouse conditions. Chapter 5 focused on the interactive effects of pH and watering regime on plant growth, nutrient uptake and antifungal activity of T. violacea plant extracts, grown hydroponically. The results showed that there were significant differences (p < 0.05) on plant growth parameters amongst the different watering regimes under normal light intensity. Broadly, two trends occurred in the results: firstly, more macro-nutrients were taken up by plants in the higher frequency watering intervals as opposed to higher tissue micronutrient nutrient values for plants grown under the lower light intensity conditions. The levels of N, P, K, Mg nutrient uptake differed significantly in plants (p < 0.001) among watering interval periods. On the other hand, plants simultaneously exposed to extended watering intervals of 21-day and low light intensity showed more bioactivity of the crude extracts against F. oxysporum in the MIC bioassay. Based on the current results, a combination of shorter watering interval and normal light intensity favoured plant growth and development, while plants grown under low light intensity with longer watering interval showed good bioactivity. Broadly, these results demonstrated that varying pH, light intensity, and watering regime can influence plant growth, secondary metabolite contents and antifungal activity of crude extracts of T. violacea. These findings will contribute to the current body of knowledge around cultivation of indigenous medicinal plants. The study will further benefit the conservation of medicinal plant initiatives, increased income of small-scale farmers and potentially promote indigenous knowledge by increasing the availability of South African medicinal plants.
28
Sequera, Mutiozabal Miren Iranzu. "Polyamine signaling pathway during environmental stress: Metabolomic approaches to elucidate spermine down-stream targets". Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/315648.
Testo completoAbstract (sommario):
Environmental stress is increasingly wearing down crop productivity. Nowadays, one of the main aims of plant research is to elucidate tolerance mechanisms to diverse stresses, in order to provide solutions by generating stress-tolerant plants. In regard with this matter, polyamine signaling pathway is of crucial importance. The major polyamines in plants (putrescine, spermidine and spermine) tend to accumulate in response to stress and are associated with a protective role. The trend of their accumulation is related to the stress the plant is sensing; in fact, polyamine biosynthetic pathway is activated at different levels depending on the stimulus, which gives a selective role to these molecules. Spermine, one of the higher polyamines, is not essential for plant growth; however, it is presently known that this molecule plays diverse protective roles under several stress factors and triggers signaling cascades implicated in plant defense. Therefore, research on spermine down-stream targets has become necessary towards the elucidation of plant tolerance responses. By the use of model plant Arabidopsis thaliana this study demonstrated the implication of this polycation on enhancement of anti-oxidative capacity by signaling connections to central hub metabolites for sugar, lipid and amino acid metabolism such as pyruvate or myo-Inositol, as well as its involvement on root morphology.El estrés medioambiental está afectando de forma paulatina la productividad de los cultivos. En la búsqueda de soluciones, uno de los principales objetivos de la investigación en fisiología de plantas, es dilucidar los mecanismos de tolerancia que se presentan ante diversos estreses, con la finalidad de generar plantas con fenotipos resistentes. En referencia a este asunto, las poliaminas y sus rutas señalizadoras son de importancia crucial. Las más abundantes en plantas (putrescina, espermidina y espermina) tienden a acumularse en respuesta al estrés por lo cual se les asocia a un rol protector, sin embargo, las tendencias de acumulación dependen del tipo de estrés que la planta es capaz de percibir. De hecho, su ruta biosintética se activa a diferentes niveles dependiendo del estímulo, lo cual les confiere un carácter selectivo. La Espermina (una de las poliaminas superiores) no es esencial para el crecimiento de la planta, no obstante, actualmente se sabe que esta molécula ejerce diversos roles protectores en una gran variedad de condiciones y además activa cascadas señalizadoras implicadas en la respuesta defensiva de la planta. En consecuencia, para dilucidar los mecanismos de tolerancia, se ha hecho necesario profundizar en las dianas de señalización por parte de la espermina. Empleando como modelo experimental Arabidopsis thaliana, el presente estudio ha demostrado la implicación de este policatión en el aumento de la capacidad anti-oxidativa a través de conexiones con metabolitos centrales en el metabolismo de azucares, lípidos y aminoácidos como es el caso del piruvato y el mio-Inositol, así como también, la implicación de esta poliamina en la morfología y ramificación de las raíces, reforzando la noción de implicación esencial por parte de esta poliamina, en la fisiología del estrés en plantas.
29
Rayan, Ahmed Mohamed. "The elucidation of the pathway of water movement in barley (Hordeum vulgare L.) seedlings using anatomical, cytological and physiological approaches". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184785.
Testo completoAbstract (sommario):
Leaves of young barley (Hordeum vulgare cv Arivat) seedlings were examined anatomically, physiologically and cytologically to infer the pathway of transpirational water movement and to understand the basis for the selective responsiveness of the growing region to osmotic stress. Vessels with open lumens were found to extend from the intercalary meristem to the expanded blade, and all vessels are present in 5 functional vascular bundles (FVB) which are separated by 20 to 30 closely packed mesophyll cells and 2 to 3 immature vascular bundles (IVB). Heat pulse transport data confirmed the anatomical suggestion that water will move throughout the leaf in open vessels and they showed also that osmotic stress will reduce water transport within 1 min, which is before transpiration is lowered. Water representing about 2 per cent of the total tissue water was obtained by centrifuging cut sections of the growing region at 5 X g against an adsorptive surface. This water is probably xylem plus cell wall water because it is easily removed, its volume is 2X that calculated to be in the vessels, and it exchanges more readily with the water in the nutrient solution than the bulk tissue water. This lack of free exchange indicates apoplastic water is somewhat separated from mesophyll cells, and it is hypothesized that osmotic stress causes sudden growth cessation and initation of metabolic changes because (a) reduced water availability together with ongoing transpiration will cause a sudden reduction in the xylem's water potential, (b) there is a lateral transmission of this reduced water potential through walls of all cells in the growing region, and (c) cells can respond in some way to changes in water potential around them. Most cells in the expanded blade are considered unresponsive to osmotic stress because transpirational water will move predominantly from the 5 FVB through the closest stomata, so only cells closest to those bundles will be altered rapidly by stress.
30
MARINO, Giovanni, Giovanni MARINO e Giovanni MARINO. "Detection of the effects of water stress on woody plants". Doctoral thesis, Università degli studi del Molise, 2014. http://hdl.handle.net/11695/66250.
Testo completoAbstract (sommario):
Climate change is increasing the chronic water scarcity in many world regions, and also in Mediterranean basin. Water is the most limiting resource for plant growth and development where the climate is characterized by high potential evaporation and low and highly variable rainfall during the growing season. Water deficit constraints all the physiological processes involved in photosynthesis. In addition, drought and heat have effects on plats secondary metabolism as the synthesis and the emission of volatile organic compounds (VOCs) that, on global scale, are able to influence the chemical and physical properties of the atmosphere. Therefore, in last years has become important to develop methods enabling the detection and the description of water relations and the physiological responses of plants experiencing water stress, that could allow the monitoring on large scale of the effects of an increasing drought condition on the vegetation.
In the present study phenotyping methods have been applied to monitor water relations, photosynthetic status and physiological responses in woody plants experiencing water stress. The aim of the study was to evaluate the reliability of remote sensing techniques, based on the passive analysis of spectral reflectance, to monitor the water status of plants and different functions that are affected by drought. Thereafter, a new application of these methods was tested for the detection of the indirect estimation of foliar isoprenoid emissions, in order to sense them remotely. In addition, the relationships and the interactions of chemical and hydraulic signals from root to leaves and the emission of VOCs were investigated in a partial root zone drought experiment on Populus nigra saplings.I cambiamenti climatici in corso stanno aumentando la cronica scarsità di acqua in molte regioni del mondo, come anche nel bacino del Mediterraneo. L'acqua è la principale risorsa limitante per la crescita e lo sviluppo delle piante, in aree in cui il clima è caratterizzato da un elevato potenziale di evaporazione e precipitazioni scarse e molto variabili nel corso delle stagioni vegetative. Il deficit idrico vincola tutti i processi fisiologici coinvolti nella fotosintesi. Inoltre, la siccità e la temperatura hanno anche effetti sul metabolismo secondario delle piante, come la sintesi e l’emissione di composti organici volatili (VOC) che, su scala globale, sono in grado di influenzare le proprietà fisiche e chimiche dell'atmosfera. Pertanto, negli ultimi anni è diventato di rilevante importanza sviluppare metodi che consentano l'individuazione e la descrizione delle relazioni idriche e le risposte fisiologiche delle piante sottoposte a stress idrico, che potrebbero consentire il monitoraggio su larga scala degli effetti della condizione crescente di scarsa disponibilità idrica sulla vegetazione. Nel presente studio sono stati applicati metodi di fenotipizzazione per monitorare le relazioni idriche, lo stato della fotosintesi e le risposte fisiologiche di piante legnose sottoposte a stress idrico. Lo scopo dello studio è stato di valutare l'applicabilità di tecniche di telerilevamento, basate sull'analisi passiva della riflettanza spettrale, per monitorare lo stato idrico e le diverse funzioni di piante legnose sottoposte a siccità. Successivamente, una nuova applicazione di questi metodi è stato impiegata per la stima indiretta delle emissioni fogliari di isoprenoidi, al fine di consentirne il rilevamento da remoto. Inoltre sono stati studiati, in un esperimento in condizione di parziale siccità della zona radicale in piante in vaso di Populus nigra, i rapporti e le interazioni esistenti tra i segnali chimici e idraulici dalle radici alle foglie e l'emissione di VOC.
31
Boyko, Oleksandr, e University of Lethbridge Faculty of Arts and Science. "Influence of various factors on plant homologuous recombination". Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2004, 2004. http://hdl.handle.net/10133/243.
Testo completoAbstract (sommario):
The genome of living organisms is constantly subjected to the environmental influences that result in different negative, negligible or positive impacts. The ability to maintain the genome integrity and simultaneously provide its flexibility is the main determinant for the evolutionary success of any species. One of the important aspects of genome maintenance is the precise regulation of the DNA repair machinery. Results reported here indicate the existence of a tight, age-dependent regulation of homologous recombination, one of the two main DNA double-strand break repair pathways. We show that recombination is influenced by conditions such as the change of temperature (cold or warm), day length, water availability (drought or overwatering stress) and salinity. These stresses not only influence the genome stability of stress-subjected generations but also change the recombination in subsequent generations. This indicates the possible involvement of homologous recombination in plant evolution and development of plant stress tolerance.xiv, 121 leaves ; 29 cm.
32
Carson, R. "The effect of salicyclic acid on the responses of plants to heat stress and virus infection". Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597317.
Testo completoAbstract (sommario):
Salicyclic acid (SA) is an important signalling molecule in plants that is involved in resistance to biotic and abiotic stresses. I examined the effect of SA on induced thermotolerance and heat shock protein (HSP) gene expression in plants. At the beginning of this project a number of studies had already been carried out with animal cells that indicated a link between salicylates and heat shock. However, no similar studies had been conducted in plants. In this study I demonstrated that SA inhibits the acquisition of induced thermotolerance in tobacco (Nicotiana tabacum L.). I investigated the possibility that SA exerts this effect by decreasing Hsp70 gene expression. However, no consistent relationship between Hsp70 gene expression and the SA-induced breakdown in thermotolerance was found. This suggests that SA is interfering with the gene expression or activity of some other HSP family, or of unknown factors. In addition to this work I have investigated the effect of SA on a plant DNA virus. It had already been shown that SA induces resistance to several positive-sense RNA viruses. I found that in Arabidopsis thaliana SA caused a significant delay in the development of symptoms induced by cauliflower mosaic virus (CaMV), a plant DNA virus. This correlated with inhibition of CaMV coat protein, as well as viral DNA and RNA, accumulation within whole Arabidopsis plants. Dissection of SA-treated, CaMV-inoculated plants revealed that SA was either suppressing CaMV replication, or cell-to-cell movement, leading to prevention of the exit of the virus from the inoculated leaf. In tobacco, SA-induced resistance to RNA viruses is antagonised by watering the plants with salicylhydroxamic acid (SHAM), an inhibitor of the mitochondrial alternative oxidase. In this study, watering Arabidopsis plants with SHAM did not antagonise SA-induced resistance to either CaMV, or to an RNA virus, turnip vein clearing virus.
33
Chávez, Martínez Ángel de Jesús. "Altered Levels of Glycosylated Sterols Affect Tomato Development and Stress Response". Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/673610.
Testo completoAbstract (sommario):
Los esteroles son una familia de compuestos triterpénicos que se presentan en forma libre (FS, por sus siglas en inglés) o conjugada, como ésteres (SE), glicósidos (SG) y acilglicósidos de esteroles (ASG). Los esteroles glicosilados (SG y ASG) y los FS son componentes de la membrana celular, donde en combinación con otros lípidos unidos a la membrana juegan un papel clave en la modulación de sus propiedades y función. Las esterol glicosiltransferasas (SGT) catalizan la glicosilación del grupo hidroxilo en la posición C-3 de los FS para producir SGs. Trabajos previos realizados en nuestro grupo de investigación han demostrado que la familia de genes SGT en tomate consta de 4 miembros (SlSGT1-4) los cuales se expresan diferencialmente. Siendo SlSGT1 el gen más expresado en los diferentes órganos del tomate, mientras que la expresión del gen SlSGT4 es apenas detectable en condiciones basales, pero se regula positivamente en respuesta a diferentes estímulos de estrés. Aunque las cuatro SlSGT codifican enzimas SlSGT funcionales, la contribución individual de cada isoforma al perfil de esteroles glicosilados, así como el impacto de una composición alterada de estos esteroles conjugados en plantas de tomate, están lejos de comprenderse. En este proyecto de tesis investigamos como los niveles alterados de esteroles glicosilados, obtenidos por silenciamiento de la expresión de SlSGT1 mediada por microARN artificial o sobreexpresión de SlSGT4 afectan el crecimiento y desarrollo del tomate y su respuesta al estrés. En el estado vegetativo, el silenciamiento de SlSGT1 dio como resultado un fenotipo pleiotrópico caracterizado por plantas más cortas y con menor área foliar. También se observó una deducción del tamaño de los frutos. En ambos casos, las alteraciones fenotípicas se asociaron a una disminución en el contenido de esteroles glicosilados, debido principalmente a una disminución en los niveles de SG, la cual fue paralela a una acumulación de FS. Por otro lado, los resultados obtenidos sugieren cierta preferencia de SlSGT1 por el estigmasterol como sustrato para la glicosilación, y demuestran que está isoforma de SGT de tomate no está involucrada en la síntesis de glicoalcaloides esteroideos (SGA), un tipo de metabolitos especializados que participan en la respuesta de defensa de las plantas. También se estudió la respuesta de las plantas silenciadas SlSGT1 al estrés biótico (infección por Botrytis cinerea) y abiótico (frio), y se observó una mayor resistencia a la infección por B. cinera, pero una menor tolerancia al estrés por frio. Estos resultados demuestran que los SG juegan un papel en el desarrollo de las plantas y frutos de tomate, así como en la respuesta al estrés. Para entender mejor los mecanismos moleculares que conllevan a estos efectos fisiológicos, se realizaron experimentos de secuenciación de ARN (RNA-seq) en hojas y frutos de las líneas silenciadas SlSGT1, los resultados de este análisis muestran una regulación negativa de varios genes involucrados en los procesos de desarrollo y respuesta a diferentes estímulos que podrían ayudar a explicar algunos de los fenotipos observados. Además, generamos plantas transgénicas de tomate sobreexpresando constitutivamente SlSGT4. Sorprendentemente, los niveles de esteroles glicosilados en estas líneas transgénicas fueron más bajos que en las plantas de tipo silvestre, probablemente como resultado de una reducción en los niveles de SlSGT1 concomitantes detectados en estas líneas. La caracterización fenotípica de estas plantas mostró que los cambios en la expresión de SlSGT4, como los observados en el silenciamiento de SlSGT1, afectan el crecimiento de las plantas y frutos de tomate, pero también la producción y germinación de semillas. En conjunto los resultados obtenidos en este trabajo muestran evidencias contundentes del importante papel que juegan los esteroles glicosilados en el crecimiento y desarrollo de las plantas y los frutos de tomate, así como en la respuesta de las plantas a estreses bióticos y abióticos, y sienta las bases para futuros estudios dirigidos a comprender con más detalle los mecanismos moleculares por los cuales los esteroles glicosilados afectan estos procesos fisiológicos.
34
Goedhart, Christian Leonard. "Influence of osmotic stress, ethanol, and a substituted pyridazinone, BAS 13-338, on the growth and lipid composition of two Chlorella species". Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53634.
Testo completoAbstract (sommario):
Chlorella vulgaris and Chlorella pyrenoidosa were compared relative to their abilities to grow at osmotic potentials of -0.1, -0.5, -1.0, -1.5, -2.0 MPa, [polyethylene glycol(PEG)-induced], and for osmotically-induced changes in lipid composition. C. vulgaris growth was inhibited as osmotic potentials decreased, while C. pyrenoidosa growth was moderately inhibited at -2.0 hPa. C. vulgaris produced increasing concentrations of triglycerides and sterol esters and decreasing levels of polar lipids and sterols as osmotic concentrations increased. Polar lipids, triglycerides, and sterols declined in C. pyrenoidosa while steryl esters remained constant. Ratios of free sterols to polar lipids were 10-fold greater in C. pyrenoidosa and were unaffected by reduced osmotic potentials. In C. vulgaris the sterol to polar lipid ratio declined.
Decreasing osmotic potentials in a continuous culture of C. vulgaris, lowered cell lipid concentration, and had no effect on chlorophyll concentrations. The greatest decrease occurred as the osmotic potential decreased from -0.1 to -0.5 HPa. Decreasing osmotic potential caused the phospholipid concentrations to decline. Saturation of triglycerides and free fatty acids increased and decreased, respectively, while polar lipids remained fairly constant. However, the sterol to phospholipid ratio increased as the osmotic potential was lowered.
BAS 13-338 (4-chloro-5-(dimethylamino)-2-phenyl-5- 3(2H)pyridazinone) had no effect on C. vulgaris resistance to osmotic stress, but caused growth inhibition as concentrations increased. However, BAS 13-338 was effective in decreasing growth inhibition of C. vulgaris grown in inhibitory levels of ethanol. BAS 13-338 had differing effects on the lipid composition of C. vulgaris when grown in PEG at an osmotic potential of -1.5 MPa compared to -0.1 MPa with 0.33% ethanol. The greatest effects were observed in the ethanol treatments where the qualitative composition of precursor sterols increased as the level of BAS 13-338 increased.
This investigation confirmed the important role of lipids in responding to environmental stress through observations of lipid responses to osmotic stress and by manipulation of lipid concentrations using BAS 13-338. Resistance to ethanol inhibition but not osmotic inhibition was achieved in the investigation.Ph. D.
35
Al-Bahrany, Abdulaziz Maatook 1960. "Physiological and biochemical responses of short staple cotton (Gossypium hirsutum L.) to salt stress". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184634.
Testo completoAbstract (sommario):
Three cotton (Gossypium hirsutum L.) germplasms (DP62, 84027, and 84033) were used to investigate the physiology of salt tolerance. Lines 84027 and 84033 were developed from the parental line DP62 and showed superior vigor under varying NaCl conditions (0.5 to 2.0 M) during germination and emergence. Proline levels increased in the leaves of all germplasms in response to increasing salinity. Varietal differences in proline levels did not reflect their variation in salt tolerance. Several physiological characteristics were also evaluated under non-saline condition in the greenhouse. There were no significant differences among germplasm sources for all parameters measured. However, salinity reduced transpiration rate, increased leaf diffusive resistance and leaf temperature for all lines. Ribosomal-RNA levels in all germplasms were evaluated after seeds were stressed for 24 hrs in various concentrations of NaCl and then germinated under normal conditions for 72 hrs. Ribosomal-RNA levels were inversely related to salt concentrations. Line 84033 followed by line 84027 had highest ribosomal-RNA content than the parental line DP62 when averaged over the four salt concentrations. Sodium content (ppm/g FW) and Cl⁻ content (ppm/g FW) were evaluated in microsomal and cell walls fractions as well as a cytoplasmic fraction which consisted of vacuoles, mitochondria, and plastids. The Cl⁻ ion exhibited a greater consistency in a concentration shift from one fraction to another as a function of time than did the Na⁺ ion. As a result, there may be a correlation between the drop in ribosomal-RNA and the amount of Cl⁻ in the microsomal fraction. Other parameters measured in the germinating seed were soluble protein (globulin), insoluble proteins (prolamin and glutelin) and fiber percentage. Variations within the germplasms were shown to exist. This study shows that even among lines that have been selected for salt tolerance from a single variety, the possibility exists that each of these lines may have a different mechanism to cope with salt stress.
36
Sumardi. "The influence of water stress on flowering and fruit production of Capsicum annuum Longum (chilli peppers)". Thesis, View thesis View thesis, 1993. http://handle.uws.edu.au:8081/1959.7/82.
Testo completoAbstract (sommario):
Severe water stress reduced the number of flowers produced by Capsicum annuum var. annuum L. Longum plants, but the timing of flower production was less affected. The use of different plant establishment techniques modified flower production. Bare rooted transplants slowed the rate of flower production in comparison with direct seeded plants or those established from cell tray transplants. Bare rooted transplants delayed the onset of water stress. The capabilities of male and female gametophytes were reduced by water stress, with the female more affected, and the interaction of male and female gametophytes was affected by moderate water stress. Moderate water stress increased the time to fruit set, but affected neither the number nor percentage of fruit set, whereas severe water stress increased the time and reduced the number and percentage. Severe water stress reduced the number and percentage of mature fruit, fruit quality indices and total fruit yield. Moderate water stress reduced the number of seeds per fruit and fruit dry weight, but total fresh weight yield was not significantly affected. The time to fruit set was negatively correlated with the quality indices of mature fruit, whereas the number of seeds was positively correlated with the same. Fertilisation determined the success of seed set, and the rapidity of fruit set. Successful fertilisation can only occur when the pollen tube arrives at a viable ovule. The processes of pollen tube growth and longevity of the ovule are the factors most critically affected by water stress in determining the yield of C. annuum Longum.
37
Rasmussen, S. L., e M. E. Stanghellini. "Effect of Salinity Stress on Development of Pythium Blight of Agrostis palustris". College of Agriculture, University of Arizona (Tucson, AZ), 1988. http://hdl.handle.net/10150/215832.
Testo completoAbstract (sommario):
Salinity stress predisposed cultivar Penncross creeping bentgrass to cottony blight caused by Pythium aphanidennatum at two temperature regimes. At 25-32 C, complete necrosis of all inoculated plants occurred at electrical conductivity (Ec) levels from 4.3-7.1 ds/m in 2 days, whereas at Ec levels of 0.5-2.8 ds/m death occurred within 3 days. At 25-27 C, complete necrosis of all inoculated plants occurred at Ec levels from 4.3-7.1 ds /m within a period of 5 days; no death was observed in control or inoculated plants at an Ec level of 0.5 ds/m. Increased salinity levels apparently affected the bentgrass rather than P. aphanidermatum. Mycelia' growth rate of the fungus was increased only slightly by salinity levels up to 7.1 ds/m. Zoospore production of P. aphanidermatum and two other species of Pythium decreased with increasing salinity levels up to 7.1 ds/m; production was completely inhibited at 14.2 ds/m.
38
Paech, Robert J. "The effect of soil moisture stress, rewatering and leaf washing on the efficacy of glyphosate on selected plant species /". St. Lucia, Qld, 2003. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17705.pdf.
Testo completo
39
Wang, Dan. "Effects of CO₂ and nitrogen on plant response to heat stress /". Connect to full text in OhioLINK ETD Center, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1225299873.
Testo completoAbstract (sommario):
Dissertation (Ph.D.)--University of Toledo, 2008.Typescript. "Submitted as partial fulfillment of the requirements for The Doctor of Philosophy Degree in Biology (Ecology-track)." Bibliography: leaves 6-9, 29-35, 71-78, 111-118, 149-153.
40
Di, Corleto Ross, e mikewood@deakin edu au. "The Evaluation of heat stress indices using physiological comparisons in an alumina refinery in a sub-tropical climate". Deakin University, 1998. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20050915.124324.
Testo completoAbstract (sommario):
The production of alumina involves the use of a process known as the Bayer process. This method involves the digestion of raw bauxite in sodium hydroxide at temperatures around 250°C. The resultant pregnant liquor then goes through a number of filtering and precipitation processes to obtain the aluminium oxide crystals which are then calcined to obtain the final product. The plant is situated in a sub tropical climate in Northern Australia and this combined with the hot nature of the process results in a potential for heat related illnesses to develop. When assessing a work environment for heat stress a heat stress index is often employed as a guideline and to date the Wet Bulb Globe Temperature (WBGT) has been the recommended index. There have been concerns over the past that the WBGT is not suited to the Northern Australian climate and in fact studies in other countries have suggested this is the case. This study was undertaken in the alumina plant situated in Gladstone Queensland to assess if WBGT was in fact the most suitable index for use or if another was more applicable. To this end three indices, Wet Bulb Globe Temperature (WBGT), Heat Stress Index (HSI) and Required Sweat Rate (SWreq) were compared and assessed using physiological monitoring of heart rate and surrogate core temperature.
A number of different jobs and locations around the plant were investigated utilising personal and environmental monitoring equipment. These results were then collated and analysed using a computer program written as part of the study for the manipulation of the environmental data . Physiological assessment was carried out using methods approved by international bodies such as National Institute for Occupational Safety & Health (NIOSH) and International Standards Organisation (ISO) and incorporated the use of a Physiological Factor developed to enable the comparison of predicted allowable exposure times and strain on the individual.
Results indicated that of the three indices tested, Required Sweat Rate was found to be the most suitable for the climate and in the environment of interest. The WBGT system was suitable in areas in the moderate temperature range (ie 28 to 32°C) but had some deficiencies above this temperature or where the relative humidity exceeded approximately 80%. It was however suitable as a first estimate or first line indicator. HSI over-estimated the physiological strain in situations of high temperatures, low air flows and exaggerated the benefit of artificial air flows on the worker in certain environments ie. fans.
41
Boyko, Oleksandr, e University of Lethbridge Faculty of Arts and Science. "The versatile role of homologous recombination in plant cell : repair of DNA damage, stress-directed genome evolution and foreign DNA integration". Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2008, 2008. http://hdl.handle.net/10133/724.
Testo completoAbstract (sommario):
Homologous recombination represents a DNA repair pathway. Its role in a plant cell is not limited to double strand break repair. It also extends to genome evolution via rearranging of DNA sequences, and has an important application in foreign DNA integration in the plant genome. Our study demonstrated that effects exerted by stress on homologous recombination and genome stability are not restricted to the exposed generation. The progeny of plants exposed to stress exhibited elevated spontaneous homologous recombination, changes in DNA methylation and higher tolerance to stress. These heritable changes are mediated by an unknown stress-inducible epigenetic signal. Furthermore, we demonstrated that using factors that enhance homologous recombination can improve the efficiency of genetic transformation by Agrobacterium. We have developed and patented a plant growth medium enhancing homologous recombination and significantly increasing the transformation frequency. The role of several other chemicals for the improvement of transformation was also evaluated.xxi, 246 leaves : ill. ; 29 cm. --
42
Attumi, Al-Arbe. "Effects of salt stress on phosphorus and sodium absorptions by soybean plants". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0001/MQ44119.pdf.
Testo completo
43
Sun, Hong. "The effect of hydrodynamic stress on plant embryo development". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33945.
Testo completoAbstract (sommario):
The effect of steady shear stress on somatic embryos were investigated in a flow chamber and evaluated at different time intervals using microscopy technique. The development of meristematic cell clusters, i.e. the immature embryos, into a polarized somatic embryo, and the effect on the localization of the suspensor cells that form during development of the immature embryos, were studied as a function of shear stresses. With the distribution and growth rate of the meristematic and suspensor cells, the effect of stress on the embryo development was established. Furthermore, the effect of shear stress on the cells at molecular level, the reaction of integrin-like proteins, the production of reactive oxygen species and the pore size of the cell walls involved in the shear stress responses, were investigated with molecular techniques.
In general, shear stress inhibits meristematic cells growth. Meristematic cells grow fastest at shear rate of 86 s-1 among all the tested shear stress conditions. By combining the results of meristematic cells growth and suspensor cells formation, it suggests that there is a critical shear rate between 86 and 140 s-1, at which no suspensor cells form. The unidirectional flow with different shear stresses helps the polarized growth and the unidirectional alignment of suspensor cells. Reactive oxygen species and integrin-like protein are detected in the stressed cells as cellular responses to shear stresses. By monitoring the pore size and uptake time of cells to macromolecules with solute-exclusive experiments, it suggests that the stressed cells expedite the response to plasmolyzing components that are used to induce maturation treatment thus affect the response to maturation stimuli.
44
Xing, Yu. "Mitogen activated protein kinase cascades mediate the regulation of antioxidant enzymes under abiotic stresses in arabidopsis". HKBU Institutional Repository, 2007. http://repository.hkbu.edu.hk/etd_ra/834.
Testo completo
45
Lucas, Anne. "Water stress and disease development in Eucalyptus marginata (jarrah) infected with Phytophthora cinnamomi". Thesis, Lucas, Anne (2003) Water stress and disease development in Eucalyptus marginata (jarrah) infected with Phytophthora cinnamomi. PhD thesis, Murdoch University, 2003. https://researchrepository.murdoch.edu.au/id/eprint/167/.
Testo completoAbstract (sommario):
The south-west of Western Australia has a Mediterranean climate and flora endemic to this area, including the keystone species, jarrah (Eucalyptus marginata), have adapted to the droughted summer conditions. The introduction of an exotic soil borne pathogen, Phytophthora cinnamomi, has challenged the survival of this and many other species. The expectation might be that plants stressed by drought are more susceptible to disease and this study examined the development of disease caused by P. cinnamomi in E. marginata and the significance of water status to that development.
Seedlings of E. marginata, clonal plants resistant to P. cinnamomi and clonal plants susceptible to P. cinnamomi, were subjected to different watering regimes in a number of field and glasshouse experiments. To determine the level of drought stress that could be imposed on container-grown E. marginata seedlings without killing them, a preliminary experiment progressively lowered the moisture levels of the substrate in their containers, until the plants reached wilting point, at which time moisture was restored to a predetermined droughted level and the process repeated. With each subsequent droughting the wilting point was lower until it was found that the seedlings could survive when only 5% of the moisture lost from container capacity to wilting point was restored.
No deaths had occurred after seedlings had been maintained at this low level for 14 days (Chapter 2). Based on these findings, the level of droughting maintained in all experiments conducted under controlled glasshouse conditions was 10% restoration. After testing the appropriateness of underbark inoculation, and a zoospore inoculation method for which no wounding was necessary, a new, non-invasive stem inoculation technique was developed. Stems were moistened in a pre-treatment, then agar plugs colonized with P. cinnamomi mycelium were held against the stem with wads of wet cotton wool and bound in place with tape. This technique resulted in a high proportion of infection in E. marginata (Chapter 4) without the need for underbark inoculation or the use of zoospores (Chapter 3). It was successfully used in a large field trial in a rehabilitated bauxite mine site with 2-year-old E. marginata clonal plants, resistant to P. cinnamomi (Chapter 5). Inoculation was in late spring after the winter and spring rainfall. This timing was to allow comparison of disease development in stressed plants under normal droughted summer conditions compared with itsdevelopment in non-stressed, irrigated plants. However, two months after inoculation, the area was deluged with unseasonal and abnormally heavy summer rainfall, negating any difference in the treatments and causing an outbreak of P. cinnamomi in the soil from an adjacent infested site. This resulted in the infection and death of some noninoculated control clones.
Monitoring of the site continued for twelve months and the advance of P. cinnamomi at the site was mapped. To test the effect of drought on the expression of P. cinnamomi under more controlled conditions, a series of glasshouse experiments was set up that simulated two possible summer conditions; drought or drought followed by abnormally high summer rainfall. These experiments utilised E. marginata seedlings and clonal plants, some resistant and some susceptible to P. cinnamomi. Plants were inoculated with P. cinnamomi prior to or after droughting. Results were compared to those of control plants that had not experienced water deficit. In both seedlings and clonal plants, the greatest extent of colonization was found in plants which had experienced no water deficit. These results indicated that drought stress played a role in inhibiting the in planta development of P. cinnamomi in all genotypes (Chapter 8). This finding was consistent for both clones, susceptible and resistant to P. cinnamomi. Most recoveries were made from non-stressed clonal plants, resistant to P. cinnamomi (Chapter 6) and more colonization was found in non-stressed clonal plants, susceptible to P. cinnamomi (Chapter 7), than was recorded for droughted plants.
The results of the field trial showed that P. cinnamomi was not recovered from some inoculated stems, which had obvious lesions, when segments were plated onto selective agar. This led to an intensive in vitro investigation into improved methods of recovery. Dark brown exudates from some segments of inoculated stems stained the surrounding agar onto which they were plated, suggesting the presence of phenolic compounds. Recovery of the pathogen from stems increased by about 10% when segments were first soaked in distilled water to leach out the phenolic compounds, then replated onto agar. Other recovery methods were also tested, including (1) baiting with Pimelea ferruginea leaves floated on the surface of water or soil filtrate, in which the infected stem segments were immersed and (2) the application of different light and temperature regimes. It was clearly shown that exudates from infected stems of field grown E. marginata inhibited the outgrowth of P. cinnamomi onto the agar. To counter the possible toxic effect that oxidized phenolics had on the growth of the P. cinnamomi, an antioxidant was added to the agar. P. cinnamomi was grown on media whichincorporated exudates from infected stems and different concentrations of ascorbic acid, with and without adjusted pH levels. There was a pronounced pH effect, with less growth on media with lower pH and no significant increase in growth of the mycelium with increased ascorbic acid concentration on pH adjusted agar (Chapter 9).
The inhibitory effect of the exudates from the stem segments led to an investigation of the possibility that, if seedlings to be planted in the rehabilitation process could be pre-treated with phenolic compounds to render them more resistant, they may have an advantage when establishing in areas where there was a potential threat of P. cinnamomi. E. marginata seeds were germinated and the seedlings grown hydroponically in a constant temperature growth room. Different concentrations of synthetic catechol, a phenolic compound naturally occurring in E. marginata, were added to the nutrient solution. Roots remained immersed in the catechol solutions for three days, before being inoculated at the root tip with zoospores of P. cinnamomi. Roots in higher concentrations of catechol were less colonized than those in lower concentrations, indicating an increased resistance to the pathogen (Chapter 10). Further work is required to determine if seedlings treated before being planted in areas threatened by an outbreak of P. cinnamomi have a greater capacity for survival, and for how long the protection persists.
The improved recovery of P. cinnamomi from infected plants is important for accurate assessment of the spread of the disease in an area and for the subsequent implementation of management strategies of containment and control. An outbreak of P. cinnamomi can impact on the revegetation of rehabilitated mine sites and the aetiology of the pathogen in mine sites needs to be more fully understood. The interaction of plant defences with the invasive pathogen has been examined in a range of environments in the field, the glasshouse, in a hydroponics system and in vitro. The results indicate that summer droughting increases the resistance of E. marginata to P. cinnamomi. However, more work is required to understand the mechanisms involved. The study also indicates that clones of E. marginata, selected as resistant to P. cinnamomi, are not resistant under all conditions and that environmental interactions should be further investigated. Lastly, for effective management strategies to be implemented it is critical that the pathogen can be confidently isolated from plants. It was shown that exudates from infected hosts inhibit the recovery of P. cinnamomi. Recovery methods that can overcome these inhibitory compounds are required. The findings invite further research into the complexity of host-pathogen relationships.
46
Lucas, Anne. "Water stress and disease development in Eucalyptus marginata (jarrah) infected with Phytophthora cinnamomi". Murdoch University, 2003. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040820.13290.
Testo completo
47
Genter, Robert B. "Population and community changes of attached-algae to zinc stress alone and in combination with selected environmental variables". Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/49778.
Testo completo
48
Odunuga, Odutayo Odutola. "Molecular characterization of the tetratricopeptide repeat-mediated interactions of murine stress-inducible protein 1 with major heat shock proteins". Thesis, Rhodes University, 2003. http://hdl.handle.net/10962/d1007724.
Testo completoAbstract (sommario):
Murine stress-inducible protein 1 (mSTI1) is a co-chaperone that is homologous with the human heat shock protein 70 (Hsp70)/heat shock protein 90 (Hsp90)-organizing protein (Hop). The two proteins are homologues of the highly conserved stress-inducible protein 1 (STI1) family of co-chaperones. The STI1 proteins interact directly and simultaneously at some stage, with Hsp70 and Hsp90 in the formation of the hetero-multi-chaperone complexes that facilitate the folding of signal transducing kinases and functional maturation of steroid hormone receptors. The interactions of mSTI1 with both Hsp70 and Hsp90 is mediated by a versatile structural protein-protein interaction motif, the tetratricopeptide repeat (TPR). The TPR motif is a degenerate 34-amino acid sequence a-helical structural motif found in a significant number of functionally unrelated proteins. This study was aimed at characterizing the structural and functional determinants in the TPR domains of mSTI1 responsible for binding to and discriminating between Hsp70 and Hsp90. Guided by data from Hop's crystal structures and amino acid sequence alignment analyses, various biochemical techniques were used to both qualitatively and quantitatively characterize the contacts necessary for the N-terminal TPR domain (TPR1) of mSTI1 to bind to the C-terminal EEVD motif of heat shock cognate protein 70 (Hsc70) and to discriminate between Hsc70 and Hsp90. Substitutions in the first TPR motif of Lys⁸ or Asn¹² did not affect binding of mSTI1 to Hsc70, while double substitution of these residues abrogated binding. A substitution in the second TPR motif of Asn⁴³ lowered but did not abrogate binding. Similarly, a deletion in the second TPR motif coupled with a substitution of Lys⁸ or Asn¹² reduced but did not abrogate binding. Steady state fluorescence and circular dichroism spectroscopies revealed that the double substitution of Lys⁸ and Asn¹² resulted in perturbations of inter-domain interactions in mSTl1. Together these results suggest that mSTI1-Hsc70 interaction requires a network of electrostatic interactions not only between charged residues in the TPR1 domain of mSTI1 and the EEVD motif of Hsc70, but also outside the TPR1 domain. It is proposed that the electrostatic interactions in the first TPR motif collectively made by Lys⁸ and Asn¹² define part of the minimum interactions required for successful mSTI1-Hsc70 interaction. In the first central TPR domain (TPR1A), single substitution of Lys³°¹ was sufficient to abrogate the mSTI1-Hsp90 interaction. Using a truncated derivative of mSTI1 incapable of binding to Hsp90, residues predicted by crystallographic data to determine Hsp70 binding specificity were substituted in the TPR1 domain. The modified protein had reduced binding to Hsc70, but showed significant binding capacity for Hsp90. In contrast, topologically equivalent substitutions on a truncated derivative of mSTI1 incapable of binding to Hsc70 did not confer Hsc70 specificity on the TPR2A domain. These data suggest that binding of Hsc70 to the TPR1 domain is more specific than binding of Hsp90 to the TPR2A domain. In addition, residues C-terminal of helix A in the second TPR motif of mSTI1 were shown to be important in determining specific binding to Hsc70. Binding assays using surface plasmon resonance spectroscopy showed that the affinities of binding of mSTI1 to Hsc70 and Hsp90 were 2 μM and 1.5 μM respectively. Preliminary in vivo studies revealed differences in the dynamics of binding of endogenous and exogenous recombinant mSTI1 with Hsc70 and Hsp90. The outcome of this study poses serious implications for the mechanisms of mSTI1 interactions with Hsc70 and Hsp90 in the cell.
49
Huggett, Jenny A. "The effect of chlorine, heat and physical stress on entrained plankton at Koeberg Nuclear Power Station". Master's thesis, University of Cape Town, 1988. http://hdl.handle.net/11427/17079.
Testo completoAbstract (sommario):
Bibliography: pages 112-138.The large volume of seawater used for cooling at Koeberg Nuclear Power Station contains many planktonic organisms which are exposed to heat, chlorine and physical stress during their passage through the system. Phytoplankton biomass, measured as chlorophyll a, was reduced by an average of 55.32% due to entrainment, and productivity was decreased by 38.30% on average, mainly due to chlorination. Zooplankton mortality averaged 22.34% for all species and 30.52% for copepods, the dominant group. The copepod Paracartia africana was used in laboratory experiments designed to simulate entrainment. Latent mortality was monitored up to 60 hours after a 30-minute application of stress factors (physical stress was not simulated), and approximately 75% of the total mortality occurred within the 30-minute period. Male Paracartia experienced higher mortalities than females. Extrapolation of these results predicts an overall entrainment mortality (including latent mortality) of 40% for copepods and 29.04% for total zooplankton, although the latter cannot be substantiated. Plankton entrainment at Koeberg was not considered to be overly detrimental to the marine environment because of the very localised area affected, rapid dispersion of heat and chlorine, rapid regeneration times of phytoplankton and some zooplankton, low abundance of commercially important species and potential recruitment from the surrounding productive Benguela upwelling region.
50
Metch, Jacob W. "Effects of Microbial Community Stress Response and Emerging Contaminants on Wastewater Treatment Plants". Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/85257.
Testo completoAbstract (sommario):
As the population in water stressed areas increases, it is critical that wastewater treatment plants (WWTPs) continue to replenish depleted water supplies, and serve as an alternative water source. WWTPs depend on microorganisms in activated sludge to remove pollutants from wastewater and therefore an understanding of how these microorganisms are affected by various conditions and pollutants is needed. Also, as consumer products and industrial processes evolve, so do the pollutants they discharge to wastewater. In order to keep pace with these changes, understanding the effects of emerging contaminants to WWTP processes is essential. The research herein assesses microbial community dynamics of the response of nitrifying microorganisms in activated sludge to variation in ammonia concentration and evaluates the impact of engineered nanoparticles on activated sludge microbial communities and other emerging pollutants, such as antibiotic resistance genes and disinfection by-products.
In order to assess microbial community dynamics of the response of nitrifying microorganisms to removal of ammonia in the feed, nitrifying activated sludge reactors were operated at various relevant temperatures and the nitrifying microbial community was characterized using activity assays and bio-molecular techniques. We found that Nitrospira spp. were the dominant nitrifying microorganisms, exhibiting stable relative abundance across multiple trials and over a range of temperatures. These results indicate the possibility of comammox bacteria in the system and highlight the complexity of nitrifying microbial communities in activated sludge relative to past understanding.
Both microbial and chemical impacts of engineered nanoparticles on WWTP processes were also investigated. Metagenomic analysis of DNA extracted from activated sludge sequencing batch reactors dosed with gold nanoparticles with varied surface coating and morphology indicated that nanoparticle morphology impacted the microbial community and antibiotic resistance gene content more than surface coating. However, nanoparticle fate was controlled by surface coating more than morphology. Disinfection by-product formation in the presence of nanoparticles during WWTP disinfection was assessed using silver, titanium dioxide, ceria, and zero valent iron nanoparticles. Silver nanoparticles were found to enhance trihalomethane formation, which was attributed to the citrate coating of the nanoparticles. These studies both raise concern over the relationship between engineered nanoparticles and other emerging concerns in WWTPs, and take a step towards informing nanoparticle design in a manner that limits their associated environmental impact.Ph. D.