2018 MU dissertations - Access restricted to UM
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Item Utilizing radiotracer and genetic approaches to determine the regulation of sucrose export in maize leaves(University of Missouri--Columbia, 2018) Tran, Thu Minh; Braun, David M.; Schoelz, James[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT AUTHOR'S REQUEST.] To sustain plant growth, development, and ultimately crop yield, carbohydrates must be transported from their site of synthesis in leaves to distant parts of the plant, such as seeds or roots. Yet little is known about the genes controlling carbohydrate distribution in plants. The main goal of this dissertation is to understand an aspect of the genetic control of carbohydrate partitioning in maize. The first chapter summarizes three mechanisms by which sugars are loaded into phloem for long-distance transport and discusses the regulation of cell-to-cell transport through plasmodesmata. I also discuss the main objectives of my dissertation research in the first chapter. Chapter 2 describes my work on developing a new tool using radioactive Fluorine-18 ([18]F) labeled sucrose to visualize sugar transport in maize plants. Physiological, genetic, and biochemical evidence showed that maize SUCROSE TRANSPORTER1 (ZmSUT1) is responsible for transporting sucrose into phloem; however, mechanistic aspects of sucrose binding by maize SUT1 are not well resolved. Specific hydroxyl groups in sucrose have been showed to participate in hydrogen bonding with SUT proteins. Hence, the main question that I asked was whether 18F substitution of hydroxyl groups at various positions within sucrose impacts the binding and the transport ability of ZmSUT1 for [18]F labeled sucrose. In chapter 3, I describes a simple and inexpensive method for constructing a fully automatic controlled growth chamber that can be easily adapted in plant biology laboratories as well as classrooms. The system can be used to study plant responses to numerous abiotic and biotic stress conditions and to grow and characterize large plants, such as maize and soybean. Chapter 4 details my characterization and cloning of carbohydrate partitioning defective33 (cpd33), a recessive mutant that accumulates excess starch and soluble sugars in the mature leaves. Based on the phenotype of cpd33 mutants, and the subcellular localization of the protein, I proposed that CPD33 functions to promote sucrose export into the phloem. Chapter 5 summarizes the findings of this dissertation and presents future research directions. Appendix A is an excerpt from a published review that I coauthored on how heat stress impacts carbohydrate partitioning and phloem transport. Appendix B is taken from a paper that I coauthored, and details my work to apply the 18F labelled sucrose transport assay to study the function of another maize sucrose transporter, Sucrose transporter2. Appendix C is taken from a paper that I coauthored to examine transcriptional responses to reactive oxygen species (ROS) accumulation in maize. Appendix D summarizes my characterization and mapping of Carbohydrate partitioning defective26 and Carbohydrate partitioning defective29.Item Plastic and evolved morphological responses of the hind limb skeleton to mechanical loading in mice(University of Missouri--Columbia, 2018) Smolinsky, Amanda; Middleton, Kevin[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT AUTHOR'S REQUEST.] Skeletal morphology is determined by a combination of genetic background and phenotypic plasticity induced by mechanical loading. The changes in limb bone morphology associated with locomotor activity through ontogeny and over evolutionary time can provide insight into the mechanisms of adaptation in locomotor systems. Here, a mouse model is used to explore the effects of mechanical loading and locomotor selection on skeletal morphology and phenotypic plasticity. The source of loading (muscular, ground reaction, or combined forces) was found to differentially affect the pattern and rate of mineral apposition at the mid-diaphysis of the femur, and the femoral cross-sectional morphology produced by running locomotion appears to be most influenced by muscular forces. Loading environment also differentially altered the gross shapes of the hind limb bones, and a blending of the influence of ground reaction and muscular forces was observed in the bones of running mice. Finally, artificial selection for increased voluntary running distance resulted in evolved changes in skeletal morphology and the plastic response of bone to mechanical loading. The results suggest regional sensitivity of skeleton to morphological change and inform our understanding of the plastic and evolutionary lability of the skeleton.Item Assessing the effects of anticoagulant rodenticides on non-target fish species(University of Missouri--Columbia, 2018) Riegerix, Rachelle Catharine-Rose; Tillitt, Donald E.[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT AUTHOR'S REQUEST.] Invasive rat species have negatively affected island ecosystems contributing to the decline and extinction of many endemic species. The eradication of rodents on islands can leads to restoration of native ecosystems. Anticoagulant rodenticides (ARs) have been an effective tool for rat eradication on many oceanic island systems (Wilmer et al 2007). The Hawaiian Islands, USA have used first generation AR, diphacinone (DPN), for pest and rodent control. Rodent populations, found on the Hawaiian Islands, have not only caused the extinction small shorebird and plant populations but have also been in direct competition for resources. ARs, in the form of a bait pellet containing 0.005% DPN, have been aerially and hand broadcast across the islands. Aerial broadcasting via helicopter has allowed for remote islands with uneven and dangerous terrain. Successful Hawaiian rodent eradications have occurred on Kure Atoll, Mokoli'i Island, and Mokapu Island. Lehua Island, a remote and uninhabited island near Ni'ihau, successfully eradicated rabbits in 2006 but was unable to eradicate the rodent population via aerial broadcasting of DPN in 2009. Following this attempt in 2009, a fish mortality event was reported on Ni'ihau and a dead whale calf also was found around the same time. Analysis of the affected fish were done and found no rodenticide in tissues. Despite these results, concerns of AR exposure to non-target species such as fish were voiced by the public. To determine AR effects on coral reef fish found in Hawaii, U.S. Geological Survey was asked to address their sensitivity as a prerequisite of another DPN aerial broadcast over Lehua Island. In December 2016, we presented our preliminary findings, which were used in the planning processes of an aerial broadcast which was conducted in August 2017. My dissertation research used acute toxicity testing, tissue analysis, and pharmacokinetics to determine the relative sensitivity of fish species to ARs. The primary objectives for my dissertation were (1) determine the median lethal dose (LD50) of three common ARs in four fish species. (2) Assess AR concentrations in fish tissues over time, effects on clotting, and AR half-lives in fish tissue. and (3) Evaluate diphacinone concentrations in coral reef fish species muscle and liver pre and post-aerial broadcasting. Direct toxicity to ARs does not appear to be a primary concern as not only did fish in this study refuse to eat rodenticide dosed bait pellets in the lab aquaria but in comparison to target and non-target species, they appear to be less sensitive. Exposure to ARs delays clotting in fish species. There is a lag-time of effects to clotting time (up to 24 hours) but clotting times return to baseline or control values between 5-7 days post dosing. DPN and BROD half-lives in fish tissues, plasma, muscle, and liver were fairly rapid. DPN and BROD half-lives in plasma were longer than half-lives in muscle and the target organ, liver. I found no detectable or quantifiable amount of DPN in the sixteen species of coral reef fish liver and muscles samples examined from Lehua Island, Hawaii. Overall, these studies suggest that the use of rodenticides near waterways with a possibility of accidental exposure to fish species, should have little to no effect on fish communities.Item Climate and land use effects on hydrologic processes and water allocation in a primarily rain-fed, agricultural watershed(University of Missouri--Columbia, 2018) Phung, Quang Anh; Thompson, Allen[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT AUTHOR'S REQUEST.] There is a need to raise our understanding of the impact of climate variability and change on hydrologic processes at the watershed scale. This is important, particularly for land managers and policymakers, in making better-informed decisions to assess adaptation strategies and to ensure that all sectors and populations can meet projected water demand. The Missouri Salt River Basin was chosen for this study due to its unique soil and agriculture-dominated land use. It is dominated by high clay content soils, making it sensitive to changes in the hydrologic condition. While numerous studies have examined hydrologic processes around this region, only a few have analyzed linkages between climate and the consequence of these changes to water allocation. One of the greatest potentials to maintain viable crop and livestock economies is to continue making gains in production efficiency, particularly in the area of rain-fed crops with the potential of increasing irrigation. Therefore, the objective of this study is to: (1) evaluate the impacts of potential climate and land use changes on the hydrologic components of the agriculturally dominated Salt River Basin; (2) evaluate the impact of climate change to agriculture management in this watershed, and determine if land use change can mitigate the climate change impacts on hydrological processes; (3) evaluate the impacts of potential climate changes on the water supply and demand of the Salt River Basin using integrated hydrological model and water allocation model approach; (4) determine if future water supply can meet the Salt River Basin catchment demands, and evaluate the future water competition among different sectors in the Salt River Basin using scenario based approach. Temperature and precipitation projections for two representative concentration pathways (RCP 4.5 moderate CO[2] level and RCP 8.5 high CO[2] level) were obtained from nineteen general circulation models statistically downscaled to better represent local conditions. These data, along with soils, land cover, land management, and topography, were input to the Soil and Water Assessment Tool (SWAT), a process-based hydrologic simulation model, to evaluate hydrologic impacts. Possible outcomes for the near (2020-2039) and far (2040-2059) future scenarios were determined. Combined climate and land use change scenarios showed distinct annual and seasonal variations in hydrological processes. Annual precipitation was projected to increase from 4% to 7%, which resulted in 14% more spring days with soil water content equal or exceeding field capacity in mid-century. However, summer precipitation was projected to decrease -- a critical factor for crop growth. Higher temperatures led to increased potential vapotranspiration during the growing season, resulting in an increased need for irrigation by 38 mm. Analysis from multiple land use scenarios indicated that converting crop and pasture land to forest coverage can potentially mitigate the effects of climate change on streamflow, thus insuring future water availability. Using hydrologic output simulations from SWAT, evaluation of water allocation strategies was performed using the water evaluation and planning (WEAP) model. By selecting priority water use strategies, WEAP enabled review of potential conflicts among users through scenario-based approaches. Operating on the principle of water balance accounting, a range of inter-related water issues facing water users, including multiple water sources, sectoral demand analyses, water conservation, water allocation priorities, and general reservoir operations, were evaluated. For this study, scenarios with different rate of irrigation expansion for crop areas were evaluated. The Ag Census data from 1997, 2002, and 2007 were analyzed to obtain the historical reported numbers of livestock in each county within the watershed. The historical livestock numbers combined with USDA agricultural projections to 2027 were used to project inventory for 2060. The results indicated that future water shortages will become more prominent in the SRB under projected climate conditions. Without any change irrigation area, the future unmet could double as a consequence of climate change from 3 million m3 to 6 million m3. Increased irrigation equal 10% of crop land results in 38.5 million m3 of unmet water demand. If water from Mark Twain can be withdrawn for agriculture purposes, the unmet demand would lower by 30% compared with the baseline period. However, under prolonged drought period, the impact of the Mark Twain Lake is limited. Finally, under all considered scenarios public water supply is not a source of water vulnerability in this region.Item Statistical analysis of clustered or multivariate interval-censored failure time data(University of Missouri--Columbia, 2018) Ma, Chenchen; Sun, Jianguo (Tony)[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT AUTHOR'S REQUEST.] Interval-censored failure time data are a type of the failure time data that often occur in clinical trials with periodic follow-ups among others. In this case, the failure time of interest cannot be observed exactly, but is known to be greater than the last observation time at which the failure has not occurred and less than or equal to the first observation time at which the failure has been observed to occur. Current status data are a special case of interval-censored data that we sometimes refer to it as the case I interval censored data. This type of censoring means that each subject is observed only once for the status of occurrence of the failure of interest, so the survival time is either left- or right-censored. Chapter 4 considers the same problem as that in Chapter 3. There are multivariate current status data with informative censoring. We propose to use the vine-copulas to describe the dependence among the failure times of interest and the censoring time. The proposed estimators are shown to be strongly consistent and the asymptotic normality and efficiency of the regression parameter estimator are established. To assess the finite sample performance of the presented methodology, an extensive simulation study is performed and suggests that the method works well in practical situations. Finally, the proposed approach is applied to a tumorigenicity experiment. Several directions for future research are discussed in Chapter 5.