Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item POLLEN TUBES FAIL TO TARGET OVULE IN THE ABSENCE OF TWO CATION/PROTON EXCHANGERS IN ARABIDOPSIS(2010) Lu, Yongxian; Sze, Heven; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Flowering plant reproduction requires precise delivery of the sperm cells to the ovule by a pollen tube. Guiding signals from female cells are being identified, though how pollen senses and responds to those cues are largely unknown. Here I provide genetic evidence that two predicted cation/proton exchangers expressed in Arabidopsis pollen play essential roles in pollen targeting of ovules. Male fertility was unchanged in single chx21 or chx23 mutant pollen; however, male-specific gene transmission was blocked in chx21chx23 double mutant. Wild-type pistil provided with a limited amount of pollen containing a mixture of single and double mutant produced ~60% less seeds compared to that produced with chx23 single mutant pollen, indicating that chx21chx23 pollen is infertile. The double mutant pollen, visualized by a pollen-specific promoter-driven GUS activity, germinated and extended a tube down the transmitting tract, but the tube failed to turn and target an ovule. Unlike wild-type pollen that targeted isolated ovules in a semi-in vivo assay, tube guidance in chx21chx23 pollen was compromised. As a first step to understand the cellular and molecular bases of tube guidance, membrane localization and activity of CHX23 was determined. GFP-tagged CHX23 was localized to endomembranes, predominantly endoplasmic reticulum (ER), in elongating pollen tubes. Furthermore, expression of CHX23 in E. coli resulted in enhanced K+ accumulation at alkaline pH, suggesting a role for CHX23 in K+ acquisition and pH homeostasis. Based on these studies and observations by others that ER oscillates and enters the apex, a simple model is proposed: Modification of localized pH by CHX21 or CHX23 enables pollen tube to sense female signals and respond by shifting directional growth at the funiculus and micropyle to target pollen tip growth towards the ovule.Item Light available to the seagrass Zostera marina when exposed to currents and waves(2009) McKone, Katie Lynn; Koch, Evamaria W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aquatic organisms are regularly exposed to varying degrees of hydrodynamic forces such as currents and waves. Seagrasses, which are rooted in the sediment, have flexible leaves, allowing them to sway back and forth with waves and deflect with currents. Furthermore, seagrasses can acclimate to local hydrodynamic forces exerted upon them by changing their morphology, which may benefit the organism via reduced drag, but may also bring disadvantages such as increased self-shading. We examined the interaction between water flow and morphology of the seagrass Zostera marina, and how this interaction affects light availability to the plant. We also assessed carbon and nutrient content of Z. marina, as the uptake of these constituents has been linked to hydrodynamic conditions and sediment composition. Our results indicate that local hydrodynamics and sediment composition induce morphological variation in the seagrass Z. marina, and that this variation influences light availability to the seagrass canopy.Item Geometrical Relationships Specifying the Phyllotactic Pattern of Aquatic Plants(2008-04-15) Kelly, Wanda Jean; Cooke, Todd J; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aquatic plants provide an opportunity to characterize the geometrical relationships of leaf patterning. A new polar-coordinate model was used to correlate meristem shape and leaf arrangement in aquatic plants. In aquatic plants, the primary geometrical relationship specifying spiral vs. whorled phyllotaxis is primordial position: primordia arising on the apical dome (as defined by displacement angles θ ≤ 90° during maximal phase) are often positioned in spiral patterns, whereas primordia arising on the subtending axis (as defined by displacement angles of θ ≥ 90° during maximal phase) are arranged in whorled patterns. A secondary geometrical relationship shows an inverse correlation between the primordial size : available space ratio and the magnitude of the Fibonacci numbers in spiral phyllotaxis or the number of leaves per whorl in whorled phyllotaxis. This geometrical analysis provides the morphological context for interpreting phyllotaxis mutants and for constructing realistic models phyllotactic patterns.Item Diversity of conjugating green algae; phylogenetic studies of a species-rich eukaryotic lineage(2007-12-21) Hall, John David; Delwiche, Charles F; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis used molecular phylogenetic techniques to investigate diversity in the conjugating green algae. The conjugating green algae are closely related to land plants and evolution within the group provides a good analogy of how evolution may have proceeded in the lineage that gave rise to land plants. I developed a dataset of the genes coxIII, psaA and rbcL with 109 taxa to determine phylogenetic relationships of the families and genera. I found that the order Zygnematales is not monophyletic and that Spirogyra was the first to branch. The order Desmidiales is monophyletic if one includes the genus Roya. The family Peniaceae is not monophyletic. The genera Cosmarium, Cylindrocystis, Mesotaenium, Penium, Spondylosium, Staurodesmus and in later studies Desmidium and Hyalotheca were found to be paraphyletic or polyphyletic. Investigation of cell division syndromes among filamentous Desmidiaceae revealed greater diversity than was previously reported. Notable among these discoveries is that Spondylosium pulchrum displays the Desmidium-type cell division, Spondylosium pulchellum the Cosmarium-type, and Spondylosium tetragonum the newly described Teilingia-type cell division. The relationship among the syndromes was inferred from phylogenetic analysis of the species that revealed a single lineage comprising filamentous and colonial species and multiple modes of cell division. This suggests that even the fundamental process of cell division can be highly modified. Results from this study also resulted in the taxonomic resurrection of the genus Didymoprium, as well as the creation of the new genus Isthmocatena and the combinations Didymoprium grevillei, Desmidium pulchrum, and Isthmocatena pulchella. Investigations of the Gonatozygaceae revealed unexpected diversity in Gonatozygon brebissonii and G. kinahani. Structural measurements were sufficient to distinguish among strains of Gonatozygon species except for Gonatozygon brebissonii. We have probably underestimated genetic and species diversity in this family. In contrast, the structurally distinct species Triploceras gracile, was found to be closely related to Micrasterias. This relationship was confirmed by sequencing and phylogenetic analysis of the nuclear encoded EF1α, EIF4 and TUA. The results of this study indicate that Triploceras is probably actually bilaterally symmetric, although it has been treated as a radially symmetric species.Item The Chemical Ecology of Hydrastis Canadensis L. (Ranunculaceae): Effects of Root Isoquinoline Alkaloids on the Hydrastis Endophyte, Fusarium oxysporum(2006-08-11) Tims, Michael; Bean, George A; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Goldenseal (Hydrastis canadensis L., Ranunculaceae) is a popular medicinal plant and has been listed in Appendix II of the Convention on International Trade in Endangered Species (CITES). The herbaceous perennial is distributed in North America under deciduous forest canopies throughout much of the south and eastern seaboard north into Canada. The rhizome, rootlets and root hairs produce medicinally active alkaloids. Although berberine, one of the Hydrastis alkaloids, has shown anti-fungal activity, the influence of Hydrastis alkaloids on the plant rhizosphere fungal ecology has not been investigated. While a Fusarium spp. was previously isolated from H. canadensis, this is the first report of a F. oxysporum endophyte isolated from Hydrastis root tissue. Additionally, F. solani was isolated from non-rhizosphere soil surrounding Hydrastis root tissue. A bioassay was developed to study the effect of goldenseal isoquinoline alkaloids on three Fusarium isolates, including the two species isolated from Hydrastis. And, in order to accurately detect the alkaloids, a HPLC-MS method was developed. The whole root extract treatment stimulated macroconidia germination and chlamydospore formation, while inducing mycotoxin production in the Hydrastis endophyte. Chlamydospore formation, macroconidial germination and mycotoxin production of PSU isolate, F. commune, was reduced by the whole root extract. The second Hydrastis isolate, F. solani, responded to the whole root extract by increasing germination rates, but with no other effects. The findings suggest that the Hydrastis root extract appears to provide selective advantage for the endophytic isolate and influences the fungal ecology associated with its root system.Item Disturbance by Fire and Its Role in the Population Biology and Distribution of a Rare Temperate Forest Herb(2006-08-25) Bourg, Norman Alan; Gill, Douglas E.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This research comprises a comprehensive investigation of the role and effects of disturbance by fire on the population biology of turkeybeard ( Xerophyllum asphodeloides : Melanthiaceae) a rare forest herb of the Appalachian Mountains. I first employ a long term monitoring dataset from a primary study population to examine demography and flowering patterns. The effects of forest disturbance on survival, fruit and seed production in this population are next investigated by evaluating the outcome of a controlled, fire and canopy alteration 'pulse' experiment. The pollination biology of X. asphodeloides in the context of the above habitat manipulation is then determined from hand pollination experiments over three flowering seasons. Lastly, the role of fire and other environmental variables in the distribution of X. asphodeloides populations at the landscape scale is assessed via the construction, cross-validation, and ground-truthing of a classification tree and geographic information system (GIS)-based predictive habitat model for the mountains of northwestern Virginia, U.S.A. The major results demonstrate that X. asphodeloides is one of the few definitively fire-adapted forest understory herbs in the eastern United States. This is due to a number of factors, including high survival and rapid resprouting after burning, fire-induced mass flowering, significantly enhanced fruit and seed production in burnt and canopy-altered habitat, and greatly increased seed production in plants with larger floral displays. Additionally, support is found for characterizing X. asphodeloides as a primarily outcrossing species with what is highly likely to be a "leaky" self-incompatibility system. Populations typically exhibit low flowering levels in undisturbed forest which in combination with their self-incompatibility subjects them to Allee effects due to pollinator limitation in most years. Disturbance by fire results in release from these limiting factors by inducing mass flowering, altering the forest habitat and increasing pollinator activity, thus facilitating outcrossing and seed set. Finally, fire frequency, elevation, slope and forest type are indicated as the main explanantory variables for predicting suitable habitat in the classification tree/GIS model. This model correctly classifies 74% of known turkeybeard presence areas and 90% of known absence areas, and results in the discovery of eight new occupied habitat patches during ground-truthing exercises. Results of this research project are valuable not only for the conservation and management of X. asphodeloides , but also make a major contribution to the understanding of disturbance regimes in Appalachian forests and have important implications for improving ecologically based management efforts of these lands.Item Characterization and Expression of RUB1 Conjugase and Cullin1-like Genes in Poplar Associated with Vegetative Bud Development and Dormancy(2006-06-12) Saritas-Yildirim, Banu; Coleman, Gary D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dormancy is an adaptive trait that ensures survival of plants in adverse growth conditions. By using phylogenetical, expression, and protein analysis, RUB1 conjugase and Cullin1 were characterized in poplar dormancy. RUB1 conjugase and Cullin1 were annotated using sequence homology approach. RUB1 conjugase was expressed in apical buds during dormancy but not detected in those of etr1-1 expressing poplars. Its transcript abundance was reduced in axillary buds, leaves and bark of etr1-1 expressing poplars compared to wild types. RUB1 conjugase expression was not affected by AVG but reduced by 50µM ACC in apical buds of etr1-1 expressing poplars. Cullin1 and EBF expression did not display significant difference in most tissues except for the Cullin1 expression in middle and bottom leaves during short-day treatments in wild types. Two novel RUB1-conjugated proteins were detected during low temperature treatments. This study has built a foundation for further analysis of targeted protein degradation in dormancy.Item COMPARATIVE ECOLOGY OF THE INVASIVE RUBUS PHOENICOLASIUS AND THE NATIVE RUBUS ARGUTUS(2005-05-26) Innis, Anne Foss; Forseth , Irwin N; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Invasive species are one of the most significant factors in human influenced global change. Management actions that prevent the spread and impacts of invasive species require knowledge of their ecological characteristics. The characteristics of the invasive wine raspberry (Rubus phoenicolasius Maxim.) and the native sawtooth blackberry (Rubus argutus Link) were examined in two forest habitats on the Maryland Coastal Plain. The invasive had greater negative effects on a common herbaceous plant (Duchesnea indica Andr. Focke) than the native. The invasive, R. phoenicolasius had higher leaf nitrogen concentrations (Nleaf), greater specific leaf areas (SLA) and higher maximal rates of photosynthesis (Amax) for a given dark respiration rate (Rd) than R. argutus. R. phoenicolasius depended less upon pollinators for fruit development and had higher fruiting rates with more seeds per fruit than the native species. In addition, seeds of R. phoenicolasius had higher germination rates. Survival of invasive seedlings was negatively affected by leaf litter additions, but seedling growth was not negatively influenced by shading. R. phoenicolasius seedlings grown in a greenhouse and inoculated with arbuscular mycorrhizal fungi produced less biomass than seedlings that were not inoculated. The distribution of R. phoenicolasius may be affected by leaf litter, but presence of AMF is probably not necessary for seedling success. A three year demographic study showed that both species were negatively impacted by drought, but the invasive recovered faster than the native species in the higher light forest. Overall, results of these studies indicate that the invasive R. phoenicolasius was more likely to competitively exclude understory herbs which can coexist with the native R. argutus. The ability of R. phoenicolasius to adapt physiologically to different light levels helps explain its ability to form dense populations under varying environmental conditions. The combination of high fruit production, plasticity and lower mortality in high light habitats is in agreement with previous studies on invasive species. The combined characteristics demonstrated by R. phoenicolasius allow this invader to spread, expand and persist in mid-successional forests in the Coastal Plain of Maryland.Item Ecological Effects of the Biocontrol Insects, Larinus Planus and Rhinocyllus Conicus, on Native Thistles(2005-05-11) Dodge, Gary Jonathan; Inouye, David W; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biological control of invasive weeds is, by nature, a delicate balance between introducing effective biological control agents and not introducing another invasive species. A disconcertingly similar suite of traits is used to describe invasive insect species and to identify appropriate biological control agents (or candidates): good control agents and invasive exotic species are good dispersers, they are good colonizers, they have high reproduction rates, and they are suited for broad distribution. It shouldn't come as a surprise that two previously released weed biological control agents can now be characterized as invasive species. The purpose of this dissertation is twofold: first, it is to explore the ecological relationship between predispersal seed predation and plant population dynamics, and second, it is to elucidate the risks to native plants involved with introduction and redistribution of exotic species. Rhinocyllus conicus and Larinus planus are Eurasian seed-head weevils, introduced and redistributed broadly across the western U.S. to control exotic thistles. Exclusion experiments on native thistles, including one that is rare and imperiled, at sites in Colorado present strong evidence that a decrease in seed production due to herbivory by both R. conicus and L. planus has lead to a reduction in recruitment of the thistles. The density of seedlings in both cases, even in the excluded units, was far below where density dependent effects may play a role in the dynamics of the thistle. Further, a survey of eight western states demonstrates established populations of L. planus and effects on seed production in multiple native species in four states. It also documents the near ubiquity and broad diet breadth of R. conicus. The process for approval of phytophagous biocontrol agents has become more cautious and more efforts are made to prevent nontarget herbivory. Nevertheless, land managers still routinely redistribute previously approved, non-regulated agent insects that appear to pose a higher risk to the native flora. The results of this research will benefit resource managers who wish to consider use of phytophagous insects as biological control agents as well as help ecologists and environmental managers understand the risk probabilities of biological control applications.Item The role of auxin on the evolution of embryo development and axis formation in land plants(2005-03-10) Poli, DorothyBelle; Cooke, Todd J.; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)ABSTRACT Title of Dissertation: THE ROLE OF AUXIN ON THE EVOLUTION OF EMBRYO DEVELOPMENT AND AXIS FORMATION IN LAND PLANTS DorothyBelle Poli, Doctor of Philosophy, 2005 Dissertation directed by: Professor Todd J. Cooke, Cell Biology and Molecular Genetics This thesis examined the role of auxin in the evolution of land plants. Several approaches were used to study how auxin regulates the development in the bryophyte sporophytes. The altered growth of isolated young sporophytes exposed to applied auxin (indole-3-acetic acid) or an auxin antagonist (p-chlorophenoxyisobutyric acid) suggested that endogenous auxin regulates the rates of axial growth in all bryophyte divisions. In the hornwort Phaeoceros personii, auxin moved at very low fluxes, was insensitive to an auxin-transport inhibitor (N-[1-naphthyl]phthalamic acid), and exhibited a polarity ratio close to 1.0, implying that auxin moves by simple diffusion. The liverwort Pellia epiphylla exhibited somewhat higher auxin fluxes, which were sensitive to transport inhibitors but lacked any measurable polarity. Thus, auxin movement in liverwort sporophytes appears to result from facilitated diffusion. In the moss Polytrichum ohioensis, auxin movement was predominantly basipetal in young sporophytes and occurred at high fluxes exceeding those measured in maize coleoptiles. In older sporophytes, acropetal auxin flux had increased beyond the level measured for basipetal flux in the specimens observed in several, but not all, seasons. The evidence from both inhibitor treatments and isolated tissues is consistent with the interpretation that the cortex carries out basipetal transport in both younger and older sporophytes, whereas the central vascular tissues carries out basipetal transport in younger sporophytes and acropetal flux in older sporophytes. Given the significant differences in fall rainfall in the collection years, the purported sensitivity of vascular tissue development may account for the seasonal variation observed in these experiments. Auxin regulators and polar transport were also used to study the regulation of the embryogenesis of the fern Marsilea vestita. Auxin biosynthesis inhibitors affected initial cell proliferation resulting in the formation of aborted embryos, p-chlorophenoxyisobutyric acid delayed growth and development in all stages of embryogenesis while -naphthaleneacetic acid mediated rapid cell proliferation that caused enlarged disorganized embryos. Polar auxin transport inhibitors caused no significant abnormalities, which suggested a limited role for polar transport in fern embryogenesis. In conclusion, this evidence suggests that auxin is ultimately involved in the establishment of the body plans in all land plant sporophytes.