UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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2006 - 200912010 - 20121

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Subject: search.filters.subject.Manganese

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    Mechanisms of Resistance to Ionizing Radiation in Extremophiles
    (2012) Webb, Kimberly Michelle; Robb, Frank T.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Extremophiles display an astonishing array of adaptations to harsh environmental conditions. We analyzed the mechanisms of ionizing radiation resistance from a diverse group of extremophilic archaea and bacteria. In Halobacterium salinarum IR resistance is conferred by antioxidant Mn2+-complexes, and protein-free cell extracts (ultrafiltrates, UFs) of super-resistant (IR+) isolates of H. salinarum had increased concentrations of Mn, PO4 and amino acids compared to the founder strain. Proteomic analysis determined that IR+ isolates with increased Mn had elevated protein expression for central carbon metabolism, suggesting a Mn-stimulated metabolic route to increased IR resistance. We examined the role of mannosylglycerate, di-myo-inositol phosphate, and trehalose in the IR resistance of various thermophiles; aerobic thermophiles had UFs which were radioprotective of enzyme activity under aerobic conditions, which is attributed to Mn, PO4 and trehalose accumulation. In contrast, anaerobic thermophile UFs did not contain significant amounts of Mn, and were radioprotective only under anaerobic conditions; we conclude the anaerobic environment confers their IR resistance.
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    The Importance of Sorting Calcium in Plant Cells: Uncovering the Roles of A Sarcoplasmic/Endoplasmic Reticulum-Like Calcium ATPase
    (2006-11-29) Li, Xiyan; Sze, Heven; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The spatial and temporal dynamics of intracellular Ca2+ in response to environmental and hormonal cues underscore the importance of Ca2+ transport during plant growth and development. The Arabidopsis thaliana genome predicts multiple genes encoding Ca2+ transporters, though the biological roles of most are unknown. Here I determine the function of AtECA3 which represents the first plant P-type 2A ATPase resembling mammalian sarcoplasmic/endoplasmic reticulum Ca ATPase (SERCA). AtECA3 (At1g10130) expressed in a yeast mutant lacking its endogenous Ca2+ pumps functionally substitutes for the defective Ca2+-ATPases. AtECA3-dependent yeast growth is blocked by thapsigargin, a specific SERCA inhibitor. The results suggest that AtECA3 is a cation pump with specificity for Ca2+ and Mn2+, and that AtECA3 enhances yeast growth on Ca2+-depleted medium or on medium with high Mn2+ by sequestrating Ca2+ or Mn2+, respectively, into endomembrane compartments. AtECA3 is expressed in pollen grains as revealed by promoter::GUS analyses and a green fluorescence protein (GFP)-tagged to AtECA3 labels endomembranes at the pollen tip. In vitro tube growth of wild-type pollen is enhanced by 10 mM Ca2+, and inhibited by thapsigargin, suggesting that AtECA3 supports tube elongation by sorting intracellular Ca2+ to appropriate compartments. This idea is supported by genetic evidence, where three T-DNA insertional mutants show 33% reduction in pollen tube length. This defect lowers sperm transmission shown as segregation distortion and decreased seed set. AtECA3 is also expressed in vascular tissues of young roots and leaves, and the GFP-tagged protein colocalizes with two Golgi markers. Three millimolar Ca2+ stimulate root growth of wild-type but not of mutants, indicating that Ca2+ accumulation in Golgi lumen is critical for growth. Root growth of eca3-4, but not of wild-type, is hypersensitive to 50 μM Mn2+. Thus loading Mn2+ into Golgi lumen by AtECA3 supports root growth. Intriguingly, mutant roots show 80% increase in apoplastic peroxidase suggesting that secretory activities became deregulated. In conclusion, I provide molecular evidence for a Golgi Ca2+/Mn2+ pump in plants. Ca2+ and Mn2+ accumulation into Golgi/secretory compartments by AtECA3 and perhaps cation release from these stores affect secretory activities critical for root growth, pollen tube elongation and male fertility.