Low plant available phosphorus limits legume growth and biological nitrogen fixation (BNF). This study examined, under controlled conditions, the relationship between soil phosphorus and alfalfa and soybean BNF on two contrasting low-P soils (Ontario and Nova Scotia) from organic dairy farms. Soluble P was applied up to 135 mg P kg-1. An optimum range of 45 to 90 mg kg-1 applied P increased soybean plant growth, nodulation, N and P uptake and BNF. Significant effects of soil type reflected greater N supplying ability and lower P sorption for the Ontario soil. Alfalfa response to soluble P application was not as apparent. In addition three potentially organically acceptable amendments (MSW compost, Crystal Green® struvite and partially solubilized rock phosphate) were evaluated as alternate sources of plant available P. Compost and struvite, applied at moderate rates, sufficiently supplied P to increase plant growth and BNF comparably to that found for soluble P fertilizer.

The objectives of this study were to examine the effects of starter N inputs and Bradyrhizobium inoculation on soybean symbiotic N fixation and grain yield under field and greenhouse conditions. The study was conducted in the Wellington and the Habitant dykelands in NS. The treatments consisted of 0, 1.5, 3 and 4.5 g/kg seed rates of inoculant and 0, 10, 20, and 30 kg/ha rates of N fertilizer. Under acidic soil conditions, the inoculated plants showed significant N fixation responses in the Wellington field while saline soil conditions suppressed N fixation in the Habitant field. The soybean grain yield showed an increasing trend with the inoculant rate 4.5 g/kg seed. The starter N fertilizer did not facilitate the soybean grain yield in the dykelands. Under controlled environment conditions, inoculant rate 3 g/kg seed alone produced the same amount of yield as 1.5 and 4.5 g/kg seed rates with N fertilizer.

Distal radius fractures are the single most common type of fracture suffered among the adult population. Presently, clinical decision making regarding optimal treatment is inconclusive. The goal of this thesis was to design, develop, and biomechanically test a novel implant for the stabilization of distal radius fractures. The novel implant is intended to provide a minimally invasive, low cost alternative to locked volar plates, while still permitting an earlier return to function. The implant consists of an angled bar with a sharp cutting edge and is inserted using a minimally invasive approach through the radial styloid. Surgical instrumentation was designed to facilitate the procedure in a controlled manner. To determine whether the implant would be capable of providing an early return to function, biomechanical tests were conducted both experimentally and numerically. Biomechanical testing showed that mechanical fixation with the novel implant does not support and early return to function.

No description available.

Symbiotic interaction of Rhizobium with roots of legume plants leads to the formation of root nodules that are capable of reducing atmospheric nitrogen. In nodule cells, bacteria are always enclosed inside the peribacteroid membrane (pbm) which is derived from the plant cell plasma membrane. The pbm mediates all the molecular exchanges between the host plant and bacteria. The pbm of soybean (Glycine max) nodules induced by Bradyrhizobium japonicum was characterized for the presence of nodule-specific proteins (nodulins), which may be involved in some of the nodule-specific roles the pbm plays. The pbm was found to contain a number of nodulins, and most of them were shown to be of plant origin. The peribacteroid fluid (pbf) was also purified and shown to contain nodulins. Some of the pbf proteins were highly glycosylated. Immunological localization at the electron microscopic level has shown that pbm nodulins are inserted specifically in the pbm; almost none are detected in the plasma membrane (pm) of infected cells even though the pbm is derived from it. The amino acid sequences of three different pbm nodulins (nodulin-23, -24 and -26) do not share significant primary structure homology, neither do their tentative secondary structures. Our results do not preclude targeting based on pbm-nodulin-specific feature(s) of the proteins; but it is possible that pbm-specific localization is achieved by differential rates of membrane synthesis, or turnover, in pbm as compared to the plasma membrane.

This research investigates the effects of the human body on the mechanical, chemical, and morphological properties of the surface of internal fixation devices. Stainless steel and titanium devices that had failed were provided from the Shandong Provincial Hospital in China, along with controls: implants that had never been used. Comparative study was conducted by evaluating properties of these implants before and after implanting. The first part of the research was simulation, and a model of the human femur was analyzed in Solidworks. The stress analysis software simulated the stress distribution, the strain distribution, and the deformation pattern. Two cases were simulated: walking and car accident. The simulations showed the points of highest stress and led to the analysis of the implants that were used in those regions. The next part of the research was to experimentally examine the properties and behavior of materials. Test samples fell into one of three categories: stainless steel femur implant, stainless steel tibia implant, and titanium femur implant. Material properties were characterized and effects of the human body on each of these groups were studied. Hardness was measured using Vickers hardness indentation. Surface roughness was analyzed using light interferometric technique. Potentiodynamic polarization analysis was performed to evaluate corrosive behavior before and after implanting. Scratch tests were conducted to evaluate wear resistance and the microstructure was analyzed to further understand the morphological changes that occurred of implanted samples. Results showed that the human body generally degraded the material properties of the stainless steel femur implant. There were no measurable effects of the same on stainless steel tibia and on titanium alloy.

Soybean [Glycine max (L.) Merr.] is a tropical to subtropical legume that requires root zone temperatures (RZTs) in the 25 to 30°C range for optimal symbiotic activity. The inability of soybean to adapt to cool soil conditions limits its development and yield in short season areas. In particular, nodulation and nitrogen fixation by this crop species is sensitive to cool RZTs. The isoflavone genistein, which is the most effective plant-to-bacterium signal in the soybean nitrogen fixation symbiosis, has been used to pretreat Bradyrhizobium japonicum inocula. This resulted in increased soybean nodulation and nitrogen fixation in several studies, indicating that genistein preincubated inocula could overcome low RZT inhibition of plant growth and yield. The effectiveness of isoflavones was found to vary among soybean cultivars. Some legume cultivars apparently supply limiting amounts of the flavonoids. The objective of this thesis was to determine how soybean cultivars of different maturity groups would respond to genistein incubation of B. japonicum prior to inoculation. Two field experiments were conducted in 1997 and 1998 involving eleven soybean cultivars of three maturity groups organized in a randomized complete block design. Cells of B. japonicum, treated with genistein or not, were applied onto seeds in the furrow at the time of planting. The results of this study indicated that genistein application increased nodule number and nodule dry matter per plant, increased plant nitrogen content, grain protein and grain yield of all cultivars. There was no interaction between maturity group and genistein application, and there was no correlation between maturity groups and increase in nodulation, total biomass, nitrogen content and yield due to genistein treatment. Thus, responses of soybean cultivars of different maturity groups to genistein treatment are not related to maturity and/or yield potential.

Bone is porous and has a complex microstructure. This study considers the effect of microstructural morphology on the macrolevel mechanical properties of bone. Improved incorporation of such properties is required to advance current finite element approximations of bone behaviour. A technique to computationally generate realistic trabecular bone microstructures is developed. This provides the possibility of examining the effect of different microstructures on the macrolevel mechanical behaviour of bone. They would also permit direct incorporation of bone microstructure in macroscale finite element analyses without the prohibitive computational and experimental costs of donor-image based mesh generation. Micro- finite-element analyses are used for the first time to evaluate the macrolevel orthotropic elastic constants of cortical bone resulting from variations of microstructural morphology. It is concluded that the ratio of canal volume to tissue volume is the most powerful predictor of cortical bone elastic constants and that considerable periosteal-endosteal variations in these constants can develop with bone loss. The role of microstructure in cortical bone toughness is investigated using nano- finite-element analyses of murine cortical bone samples to simulate the initiation and propagation of microcracks. Results confirm the experimentally observed ability of canal and lacuna pores to act as stress raisers, thereby guiding the growth of microcracks. A novel and numerically efficient strain-based plasticity algorithm is presented which permits easy incorporation of strength anisotropy in finite element analyses of bone. The previously evaluated elastic properties of cortical bone are combined with the developed plasticity algorithm to conduct a detailed macro-finite-element investigation of external fixation of tibial midshaft fractures. Old patients are found to be at considerably higher risk of implant loosening under both unilateral and Ilizarov fixation, compared to younger patients.

Rubisco activase operates as the chaperone responsible for maintaining the catalytic competency of Ribulose 1,5-bisphophate carboxylase oxygenase (Rubisco) in plants. Rubisco is notoriously inefficient, rapidly self-inactivating under physiological conditions. Rubisco activase uses the power released from the hydrolysis of ATP to power a conformational change in Rubisco, reactivating it. Rubisco activase has been previously shown to form a large range of species in solution; however, little has been done to relate the size of oligomeric species and physiological activity. In this thesis data is presented from a range of biophysical techniques including analytical ultracentrifugation, static light scattering, and small angle X-ray scattering combined with activity assays to show a strong relationship between oligomeric state and activity. The results suggest that small oligomers comprising 2-4 subunits are sufficient to attain full specific activity, a highly unusual property for enzymes from the AAA+ family. Studies utilising a number of Rubisco activase variants enabled the determination of how Rubisco and Rubisco activase may interact within a plant cell. A detailed characterisation of the α-, β-, and a mixture of isoforms further broadened our knowledge on the oligomerisation of Rubisco activase. Of particular importance was the discovery of a thermally stable hexameric Rubisco activase variant. It is hoped that these findings may contribute to development of more heat tolerant Rubisco activase and lead research into more drought resilient crop plants.

This project was designed to assess the ability of natural sediment microbial communities and single species microbial populations to preferentially utilize inorganic forms of nitrogen (ammonium, NH4-N, and nitrate, NO3-N, specifically). The first chapter addressed two primary questions: 1) Do sediment microbial communities preferentially assimilate NH4-N or NO3-N?; and, 2) Does preferential uptake of nitrogen change with increased NH4-N or NO3-N availability? The second chapter furthered these analyses by assessing shifts in microbial nitrogen assimilation in response to sustained nitrogen enrichments. Primary questions addressed were: 1) Are microbial communities able to adapt to nitrogen enrichment and preferentially utilize a more available source?; and, 2) Are initial microbial responses to nitrogen enrichment different from sustained responses? Questions were addressed with in vitro laboratory experiments quantifying microbial activity. Overall, microbial community activity changed in response to the form of nitrogen available, enrichment type, and duration of exposure. Data demonstrate sediment microbial communities in the Midwestern US may prefer NO3-N over other forms of nitrogen. However, microbial communities became saturated with NO3-N with increases in concentrations >0.75 mg NO3-N/L. Microbial communities were able to adapt to higher nitrogen concentration and increase rates of assimilation for both NH4-N and NO3-N. Thus, microbial communities are robust in response to nitrogen increases in and ecosystem, even in high nitrogen environments like the Midwestern US. / Preferential uptake of available nitrogen forms -- Adaptive uptake in microbial communities. / Department of Biology