Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. Includes bibliographical references (leaves 105-111).

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 147-155).

The model legume, Medicago truncatula, is able to enter into a symbiotic relationship with soil bacteria, known as rhizobia. This relationship involves a carbon for nitrogen exchange in which the plant provides reduced carbon from photosynthesis in exchange for reduced, or “fixed” atmospheric nitrogen, which allows the plant to thrive in nitrogen depleted soils. Rhizobia infect and enter plant root organs, known as nodules, where they reside inside the plant cell in a novel organelle, known as the symbiosome where nitrogen fixation occurs. the symbiosome is enriched in plant proteins, however, little is known about the mechanisms that direct plant proteins to the symbiosome. Using the M. truncatula ENOD8 (MtENOD8) protein as a model to explore symbiosome protein targeting, 3-cis domains were identified within MtENOD8 capable of directing green fluorescent protein (GFP) to the symbiosome, including its N-terminal signal peptide (SP). the SP delivered GFP to the vacuole in the absence of nodules suggesting that symbiosome proteins share a common targeting pathway with vacuolar proteins. a time course analysis during nodulation indicated that there is a nodule specific redirection of MtENOD8-SP from the vacuole to the symbiosome in a MtNIP/LATD dependent manner. GFP expression by the MtENOD8 promoter revealed spatial discrepancy between promoter activity and protein localization. in situ localization of MtENOD8 mRNA showed localization to infected cells, where the protein is found, suggesting mRNA cell-to-cell movement. Expression of MtENOD8 in Arabidopsis showed that the SP did not direct GFP to the vacuole indicating that vacuolar targeting of MtENOD8’s SP may be legume specific. Taken together, the research presented here indicates that the MtENOD8 symbiosome protein has evolved redundant domains for targeting, which has part of a common pathway with vacuolar proteins. Observed spatial discrepancy between the MtENOD8 promoter and protein shows additional mechanisms of gene regulation through cell-to-cell mRNA movement, previously unknown in nodules.

Transition metal and rare earth element (REE) data are presented for various sedimentary materials from two Manganese Nodule Program (MANOP) sites in the eastern tropical Pacific. These data constrain the sources of elemental supply to the seafloor and the processes that control ferromanganese nodule genesis. Investigation of elemental partitioning between suspended particles, sediments, ferromanganese nodules, crusts, and micronodules indicates that particle settling dominates REE supply to the seafloor at MANOP site H. Partitioning of the particle flux reveals that although detrital and labile particles both convey REE to H sediments and nodules, labile biogenic debris is the primary source of REE accreted by site H nodules. Evidence from REE abundance patterns and correlations of REE with other elements define three basic processes of nodule accretion: (1) hydrogenous or direct seawater precipitation; (2) oxic diagenesis, referring to a variety of ferromanganese accretion processes which occur in oxic sediments; and (3) suboxic diagenesis, in which Mn is mobilized by the oxidation of sedimentary organic matter. The REE geochemistry of site H nodules suggests an additional accretionary process, resulting from the degradation of labile organic matter in an oxic environment. Contrasts in REE patterns, major element compositions, and fluxes of various elements in sedimentary samples from MANOP site H (a nodule-bearing site) with site M (a nodule-free site) reveal differences in the sources of material to the seafloor in the two environments. Geochemical data imply a greater hydrothermal influence and a greater accumulation of organic carbon in site M sediments relative to those at site H. Comparisons of the REE and major element geochemistry of H and M sediment traps, sediments, and crusts, as well as nodules from site H, imply that the reductive mobilization of Mn and geochemically similar elements is controlled primarily by surface water biological productivity and the accumulation of organic carbon in the sediments. The organic flux to the sediments determines the degree of depletion of oxidants, which governs the reduction, mobilization, and supply of metals to nodule surfaces. It appears that the depth to the Mn redox boundary and possibly seasonal variations in the flux of organic material to the seafloor determine whether nodules grow or whether Mn is exported to bottom waters. / Graduation date: 1985

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 96-97).

Thesis (Ph. D.)--Massachusetts Institute of Technology, 1968. / Prepared under: DSR 78841 Contract nonr 1841(74), NR 083-157, Office of Naval Research. DSR 76788, contract AT (30-1)-905, Atomic Energy Commission. Includes bibliographical references (p. 203-216).

Thesis (M.S.)--University of Wisconsin, 1970. / Typescript (photocopy). eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. [97]-101).

No description available.

Thesis (Ph. D.)--University of London, 1967. / Bibliography: leaves 285-307.