Trifolium ambiguum (Caucasian clover) is being released in New Zealand for use in areas where growth of T. repens (white clover) is marginal. Although closely related to T. repens, T. ambiguum has unique and highly specific nodulation requirements and as rhizobial strains capable of effectively nodulating T. ambiguum are not naturally found in New Zealand soils, they must be introduced with the seed. Rhizobium leguminosarum bv. trifolii strains such as ICC105 form effective nodules on T. ambiguum but ineffective (Fix⁻) nodules on T. repens. The T. repens nodules nevertheless develop normally and contain bacteroids. R. l. bv. trifolii strains that are effective on T. repens such as NZP561, fail to nodulate T. ambiguum. As the host-specific nitrogen fixation defect of Caucasian clover rhizobia on T. repens has potentially adverse agronomic implications, the genetic basis for this Fix⁻ phenotype was investigated. Rhizobium leguminosarum bv. trifolii strain ICC105 was converted to Fix⁺ on T. repens by the introduction of an 18-kb fragment of DNA from a white clover rhizobial strain (NZP514) symbiotic plasmid. This fragment contained several nif and fix genes, including nifHDKEN, fixABCX, nifA, nifB, fdxN and fixU. Tn5 mutation of these white clover rhizobial genes demonstrated that most were required to impart the Fix⁺ phenotype on T. repens to ICC105, with the exception of nifA. Mutagenesis of the ICC105 nifA gene and subsequent complementation with various combinations of the white clover rhizobia nif/fix genes as well as transcriptional lacZ fusion studies of the ICC105 nifA and nifH genes demonstrated that ICC105 nifA is expressed and functional during the ineffective nodulation of T. repens and able to activate expression of nifHDKEN and fixABCX operons derived from white clover rhizobium but not from ICC105. Sequence analysis and comparison of the intergenic region between the divergently transcribed nif/fix operons revealed a conserved 111-bp region found between the nifH/fixA promoters of Caucasian clover rhizobia, but not in white clover rhizobia. Attempts to modify this region in ICC105 failed in creating a strain which was Fix⁺ on T. repens; however recombination of the nifHD/fixAB region from a white clover rhizobium into the ICC105 genome produced several strains with a �swapped� nitrogen fixation phenotype (i.e. Fix⁺ on T. repens and Fix⁻ on T. ambiguum). A hypothesis was therefore proposed by which differences in the nifH/fixA promoter regions of Caucasian clover rhizobia and white clover rhizobia modulate the expression of the upstream genes in response to the particular plant host they are nodulating. The incompatibility between the symbiotic plasmid of R. l. bv. trifolii ICC105 and the white clover rhizobium symbiotic plasmid cointegrate, pPN1, was also investigated and potential regions of each plasmid involved in this incompatibility were identified. The research presented in this thesis has contributed to the genetic knowledge of the nitrogen fixation genes, and regulation of these genes in R. l. bv. trifolii. It has also provided progress towards the goal of creating a suitable inoculant strain for T. ambiguum that is able to fix nitrogen in symbiosis with both T. repens and T. ambiguum.

Bibliography: leaves 216-231. / xvii, 231, [99] leaves : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Examines the sliding capability of external fixators under load and describes the development and testing of an external fixator capable of providing axial cyclic motion to a fracture site while a patient is walking. / Thesis (M.D.)--University of Adelaide, Dept. of Orthopaedics and Trauma, 1999?

Bibliography: leaves 189-210 / xxxiv, 210 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agricultural Biochemistry, 1987

Bibliography: leaves 153-179. / xvi, 179 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Annual species of Medicago, or medics, are important pasture legumes in the neutral to alkaline soils of southern Australia but their nodulation and nitrogen fixation processes are retarded by soil nitrate. This study ascertains whether an observed tolerance to nitrate among medic species can be substantiated, and attempts to understand the underlying factors responsible. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, (1995)

Bibliography: leaves 153-179. Annual species of Medicago, or medics, are important pasture legumes in the neutral to alkaline soils of southern Australia but their nodulation and nitrogen fixation processes are retarded by soil nitrate. This study ascertains whether an observed tolerance to nitrate among medic species can be substantiated, and attempts to understand the underlying factors responsible.

Bibliography: leaves 209-254. Experiments detailed in this thesis, evaluate the impact of various herbicides and herbicide mixtures on the growth, nodulation and nitrogen fixation of annual pasture legumes, the efficacy of the herbicides for weed control, and the potential role of mechanical defoliation to replace herbicides, leading to lower cost and more sustainable farming systems.

共著者あり。共著者名:Yoshida Toshikazu, Fukushima Kikuro. / Hokkaido University (北海道大学) / 博士 / 医学

Graduation date: 1998

While there is continuing interest in bioresorbable materials for orthopedic fixation devices, the major challenge in utilizing these materials in load-bearing applications is creating materials sufficiently stiff and strong to sustain loads throughout healing while maintaining fracture stability. The primary aim of this study is to quantify the degradation rate of a bioresorbable material system, then use this degradation rate to determine the material response of an orthopedic device made of the same material as healing progresses. The present research focuses on the development and characterization of a material system consisting of carbon foam infiltrated with hydroxyapatite (HA) reinforced poly(D,L-lactide)-co-poly(glycolide) (PDLGA). A processing technique is developed to infiltrate carbon foam with HA/PDLGA and material morphology is investigated. Additionally, short-term rat osteoblast cell studies are undertaken to establish a starting point for material biocompatibility. Degradation experiments are conducted to elicit the time-dependent properties of the material system at the material scale. These properties are then incorporated into computational models of an internal plate attached to a fractured human femur to design and predict the material response to applied physiological loads. Results from this work demonstrate the importance of material dissolution rate as well as material strength when designing internal fixation plates.

Reading requires the orchestration of visual, attentional, language-related, and oculomotor processing constraints. This study replicates previous effects of frequency, predictability, and length of fixated words on fixation durations in natural reading and demonstrates new effects of these variables related to previous and next words. Results are based on fixation durations recorded from 222 persons, each reading 144 sentences. Such evidence for distributed processing of words across fixation durations challenges psycholinguistic immediacy-of-processing and eye-mind assumptions. Most of the time the mind processes several words in parallel at different perceptual and cognitive levels. Eye movements can help to unravel these processes.