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In this thesis is described the identification and characterisation of two morphogenesis mutants of Arabidopsis thaliana. One, vertically challenged (vch1) exhibits much reduced cellular elongation. The second, altered suspensor fate (asf1) is embryonic- lethal. A thorough phenotypic analysis of both mutants is presented, as are the results of genetic analysis. Vch1 exhibits a severe reduction in cellular elongation throughout the plant, resulting in a dwarfed phenotype. Despite its stunted morphology, vch1 exhibits normal cellular patterning, demonstrating that cell morphogenesis can be uncoupled from correct cellular pattern formation, vch1 follows a normal life history by all parameters examined demonstrating that the timing of developmental events can be uncoupled from correct morphogenesis. The phenotype of vch1 cannot be rescued by the exogenous supply of a range of hormones, signalling inhibitors or growth conditions, although it can respond to each, in a proportionately similar manner to wild type seedlings. No defects in cell wall architecture nor in cytoskeletal organisation were detected during this study. Speculative models for the role of the VCH gene are proposed. In asf1, the embryo proper arrests at the transition stage of embryogenesis. The wild type suspensor is a single file of cells which serves to anchor the embryo proper to the maternal tissue and acts as a conduit for, and source of, nutrients to the developing embryo. In asf1, suspensor cells undergo inappropriate proliferation following the arrest of the embryo proper. Evidence is presented from cytological and ultrastructural examination, and expression of spatially restricted gus-fusion marker genes, that the ectopically divided suspensor cells take on aspects of embryo proper-like character. Models for the role of the ASF1 gene are proposed. It is likely that the mutant phenotype results from disruption of intercellular communication between the embryo proper and suspensor.

P. elliottii Engelm. var. elliottii is an important exotic plantation species in Zimbabwe, where it is grown for saw-timber and resin production. Three progeny tests, originating from factorial matings between parents selected in plantations, were assessed at five, eight and 15 years. The objectives of the study were to characterise quantitative genetic variation in the population through the estimation of genetic parameters, and to use these parameters in combined indices to select for specified breeding objectives for P. elliottii in Zimbabwe. All traits of interest were under a reasonable degree of additive genetic control, and the magnitudes of nonadditive genetic variances were almost invariably much less than those of additive genetic variances. Narrow-sense heritabilities for growth traits, wood density and resin yield were moderate to high, ranging from 0.3 - 0.42; those for stem straightness and branching traits were lower, ranging between 0.10 and 0.25. Genetic correlations at each of the assessment ages were more variable; of most consequence for this study were the slight negative correlations between wood density and both stem diameter and volume, and the slight positive correlation between density and height. Age-age correlations for growth traits were high, indicating potential for early selection. Age-age correlations for other traits ranged from moderately negative to highly positive. Although statistically significant for many traits, genotype-environment interaction was judged by a number of criteria to be of little practical importance. No one site was the most efficient for selection across the range of traits for establishment at other sites; rather, a set of pooled parameters was estimated for application on sites typical of those on which commercial plantations of P. elliottii are established. Selection indices were constructed for four breeding objectives, representing differing assumptions about the relative importance of saw-timber and resin production. Indices for both direct and indirect selection were compared in terms of genetic gain, efficiency and accuracy, which were influenced by the differential weighting of traits in the breeding objective. The highest gains, efficiency and accuracies were for the breeding objective of saw-timber only; increasing the emphasis on resin production reduced each of these parameters, and also had a more adverse impact on wood density. For a breeding objective corresponding to or emphasizing saw-timber production, selection based on diameter or height at five years was best; selection on the latter has the advantage of maintaining wood density at around its present level. Should resin production also be important, resin yield or a correlated trait must be included in the index. Efficiencies of indirect selection were highest at five years, regardless of the breeding objective or selection criteria considered. The lack of economic information was a considerable hinderance in conducting these analyses. The construction of more complete indices, incorporating information from all siblings represented in the factorial mating design, was also investigated for the breeding objective of saw-timber production. These indices were compared in terms of gain and accuracy, and their effect on population structure in the subsequent generation. Selection based on the most complete index resulted in the greatest gain and accuracy, but also in the greatest reduction in additive genetic variance in the next generation. These results highlight the dilemma facing breeders charged both with achieving gains in the short term and maintaining diversity over the longer term. Breeding strategies which facilitate differential intensities of selection and breeding, and the maintenance of a large effective population size, are seen as the best means to resolve these conflicting demands; some implications for the breeding population of P. elliottii in Zimbabwe are discussed.

The organization and structure of the leghemoglobin (Lb) genes in soybean have been investigated. Using molecular cloning techniques, a Lb-cDNA recombinant molecule, pLb1, was prepared and characterized. Hybridization of this clone of genomic DNA revealed the presence of at least seven Lb genes in the soybean genome. The arrangement of these genes appeared to be the same in DNA isolated from infected or uninfected tissues. The plasmid pLb1 was also used to isolate three Lb sequences from a genomic library constructed in (lamda) Charon4 vector. Nucleotide sequence analysis showed that one Lb gene, present on an 11.5 kilobases (kb) Eco RI genomic fragment, spans about 1 200 nucleotides and appears to code for Lbc(,3). Its coding sequence is interrupted at amino acid positions 32 to 33, 68 to 69 and 103 to 104. The intervening sequences, as well as the 5' and 3' flanking regions of this gene, contain some consensus sequences found in other eukaryotic genes. The length of the 5'-untranslated region is 49 bases as determined by nuclease S1 mapping. R-loop analysis of the recombinant phage containing the 11.5 kb Eco RI fragment showed that another Lb gene is located 2.5 kb away. The nucleotide sequences of the second gene showed that this gene is incomplete, containing only two exons. The deduced amino acid sequence of this gene, although showing 78% homology with the corresponding region of the other Lb gene, is not represented in any of the known Lb proteins. Both genes are oriented in the same direction with respect to the coding strand. Analysis of the sequence present in a second genomic clone containing a 4.2 kb Eco RI fragment revealed a truncated Lb gene showing homology with the last exon and the non-coding region at the 3' end of the two other Lb genes. A very high homology is found among the nucleotide sequence of the Lbc(,3), Lba and Lbc(,1) genes. Comparison of the intervening sequences of these genes indicated that they diverged mainly through the creatio

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 16, 2009). Thesis advisor: Dr. Kristin D. Bilyeu. Includes bibliographical references.

Thesis (Ph.D.) - University of Queensland, 2003. / Includes bibliography.

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