Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 11, 2010). Includes bibliographical references.

Thesis (M.S.)--University of North Texas, Aug., 2007. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of Adelaide, Dept. of Plant Science, 1995? / Includes bibliographical references (leaves 151-177).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1939. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Hannover, University, Diss., 2005.

Hannover, University, Diss., 2004.

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.

Bibliography: leaves 151-177.

No description available.

Germination strategies and early seedling development of selected Medicago and Hedysarum species were evaluated to identify plants with high potential for range rehabilitation in central Tunisia. Temperature (5°C to 25°C) and water stress (0 MPa to -0.8 MPa) affected the germination percentage of all Medicago and Hedysarum species. Water stress had a greater effect on percent germination than did temperature, however, the nature of the effect of water potential depended on temperature. Australian medics were more depressed by temperature extremes and low water potential than were Tunisian accessions. Optimum germination of Medicago polvmorpha var. Circle Valley and Medicago trucatula var. Jemalong was at 15 °C and 0 MPa. Germination was highly reduced at higher temperatures and water stress. Tunisian Medicago truncatula germinated better at lower temperatures (5 °C to 15 °C). Hedysarum carnosum germinated more completely at high temperatures. (15°C to 20°C). Medicago laciniata germinated well across a wide range of temperature but germination decreased as water stress increased. Rapid rates of root elongation are beneficial to plants in semiarid environments. High temperature accelerated rates of root elongation and low temperature retarded the rates. The degree of retardation varied with the species and the temperature range. Maximum root elongation occurred at 15°C and minimum root elongation occurred at 5°C. Medicago laciniata had the fastest root elongation rate at 5°C and 15°C . Medicago truncatula was equal to Medicago laciniata at 5°C. Hedysarum carnosum had rapid root elongation at 10°C and 15°C compared to 5°C. A Tunisian accession Medicago polymorpha had the slowest root elongation at all temperatures. A quantitative growth analysis was used to assess the effect of environmental conditions on the species performance over a period of 49 days. Mean relative growth rate (mRGR) varied among species. This variation suggested size hierarchies in relative performance among species. The largest plant, Tunisian Medicago truncatula had the largest mRGR and the smallest plant, The Tunisian Medicago polvmorpha had the lowest mRGR. The derived parameters, leaf area ratio (LAR) and unit leaf ratio (ULR), were not consistent with the size hierarchies obtained by mRGR. The Root to shoot ratio (R/S) varied among the species. The Tunisan Medicago truncatula had high root to shoot ratios at low temperature and its R/S ratio decreased at higher temperature. Slow growing species had high R/S ratio. Medicago laciniata was an exception, it produced low R/S ratio because of its long, and thin root system. / Graduation date: 1991