Hybridisation, polyploidy and asexual (apomictic) reproduction have given rise to high genetic diversity and taxonomic complexity in Avon Gorge Sorbus. Sorbus aria (a sexual diploid species) in particular has been implicated as a primary contributor to Sorbus diversification through hybridisations with polyploid taxa. It may also play a major role in the reproductive success of apomictic taxa by acting as pollen parent for pseudogamy (the partly-sexual formation of endosperm in asexual seed). The hypothesis was that S. aria acts as the primary pollen parent for endemic pseudogamous Sorbus taxa and in doing so facilitates evolutionary diversification of Sorbus in the Avon Gorge through rare inter-taxon hybridisation. Observations of flowering periods and insect pollinators showed that intra-generic synchronous flowering and the use of generalist pollinators allow for the movement of pollen among Sorbus flowers and the occurrence of inter-taxon mating events between Sorbus taxa growing in the Gorge. Pollination experiments, combined with molecular marker analyses of adults and progeny, showed that outcrossing occurs in the sexual diploids, which may encourage inter-taxon hybridisation. The tetraploid taxa were found to reproduce by apomixis and pseudogamy with self-compatibility which together are advantageous in the perpetuation of these taxa. The triploids were also found to be apomictic and pseudogamous, but they are self-incompatible and rely on inter-taxon pollen for seed set. A lack of hybrid progeny from open pollinations indicated hybridisation occurs rarely in the natural populations. Genotyping and flow cytometric analyses of endosperm in seeds from triploid taxa provided conclusive evidence that diploid S. aria is involved in their reproductive success as a pseudogamous pollen parent. Seed viability testing showed low seed fertility in the polyploids compared to S. aria, suggesting new polyploids may struggle to establish populations. Finally, in light of current conservation concerns for local endemic Sorbus, research-based recommendations are made to provide a foundation for conservation strategies that aim to protect rare, endemic Sorbus taxa, Sorbus taxonomic complexity and the evolutionary processes that drive Sorbus diversification in the Avon Gorge.

Prosopis juliflora (Sw.) DC. and P. pallida (H.&.B. ex Willd.) H.B.K. occur naturally in the Americas and they are morphologically similar species. They are multipurpose trees and their ability to grow in poor soil conditions has encouraged their introduction throughout the arid regions of the tropics and semi tropics. The taxonomy of the genus Prosopis Linnaeus emend. Burkart is unclear and a revision of the genus is suggested by several studies. Due to their similarity, the differentiation of P. juliflora and P. pallida is difficult. Although there has been some success in differentiating the species using ploidy, leaf morphology and molecular markers, further approaches are required. This study looked for suitable cytological characters and molecular markers that would differentiate the two tropical species. The cytological character analysis allowed for the development of a dichotomous key for their identification based on leaf stomatal characters. Stomatal length and epidermal cell density are the two characters on which the keys were developed. Correct identification of the species will allow for genetic improvement programmes and conservation efforts in the native regions. Multivariate statistical analysis showed that P. juliflora and P. pallida were separable into two groups. This could help in the classification of unknown herbarium specimens or previously misidentified samples. The phylogenetic relationship of the two species is also disputed and previous RAPD studies show close genetic similarity between the two species, suggesting a reconsideration of the series within section Algarobia. There are also disputes regarding the geographical distribution of both species and naming of new species. In this study, similarity index analysis and cluster analysis on the RAPD data revealed P. juliflora to be more closely related to North American Prosopis spp. than to P. pallida.

The oleoresin exudates from two species of Commiphora trees, and their extracts, were evaluated as novel methods of controlling terrestrial molluscs. Various test methods were employed including terraria trials, leaf disc assays, caged field trials and spray trials. Laboratory terraria trials with C. molmol (myrrh) and C. guidotti (opoponax) oleoresins, showed them to be effective repellent barriers against the terrestrial molluscs Deroceras reticulatum, Arion hortensis and Helix aspersa. Solid repellent barriers comprised of reduced amounts of myrrh oleoresin, mixed with inert materials (sawdust, corncob and sharp sand) and sawdust coated with extracts of myrrh and opoponax, were also very effective in repelling terrestrial molluscs. The botanical origin of myrrh and opoponax oleoresins were confirmed using gas chromatography-mass spectrometry (GC-MS) analytical techniques. The chemical compounds identified for myrrh were consistent with those reported for C. molmol, comprising mainly of sesquiterpenes and furano-sesquiterpenes, whilst the chemical compounds identified for opoponax were consistent with those reported for C. guidotti, comprising mainly of monoterpenes and sesquiterpenes. Comparison of the chemicals identified for commercial myrrh (Yemeni) and Somali myrrh (Guban) showed them both to contain the same bouquet of chemical compounds. Differences were observed in the gas chromatographic profile of Somali and Yemeni myrrh. Somali myrrh contained high levels of β-elemene, whilst Yemeni myrrh was dominated by the furano-sequiterpenes, curzerene and Furanoeudesma-1,3-diene. a-Santalene was the major sesquiterpene identified for the liquid extracts of opoponax, whilst /ra s-p-ocimene was the dominant chemical identified for the volatile odour associated with the opoponax oleoresin and its extracts. Leaf disc assays, with D. reticulatum slugs, confirmed the extracts of myrrh and opoponax, to be strong antifeedants at concentrations of 0.5% and 1% respectively. Both extracts significantly reduced the feeding behaviour of the slugs. A number of terpenoid chemicals were also evaluated, using the leaf disc assay, and showed significant antifeedant properties. The most potent of these chemicals was found to be /ra/ -p-ocimene, a major component of opoponax, and was found to possess both antifeedant and molluscicidal properties towards slugs. The molluscicidal nature of this monoterpene depended upon the polarity of the medium used to prepare it. Leaf discs assays with H. apersa snails, showed that higher concentrations of myrrh and opoponax extracts (3%) was required to deter the snails from feeding on the lettuce leaf discs. In addition higher concentration levels of rra s-p-ocimene (5%) was required to cause a similar antifeedant effect. In contrast to the slugs, no snail mortality was observed with these strong antifeedant extracts, however 100% snail mortality was observed after treating lettuce leaf discs with pure /rara'-p-ocimene oil. Emulsion stability was found to be dependent upon nature of the non-ionic surfactant incorporated into the formulation. Oil in water emulsions based on myrrh, opoponax and rra s-p-ocimene oils, containing 3 to 5% surfactant, were stable for time periods ranging from two weeks to more than 10 months. Emulsions based on Synperonic 91/8 were stable for two weeks, whilst those containing Tween 80 and Tween 20 were stable for approximately 10 months to one year. Caged field trials with repellent physical barriers comprised of 100% myrrh and opoponax oleoresins, reduced myrrh oleoresin mixed with inert substrates, and sawdust treated with ethanol and essential oil extracts of myrrh, all showed significant repellency properties towards D. reticulatum slugs for 14 days. Spray trials with myrrh, opoponax and rnms-p-ocimene, under controlled temperature conditions, showed them to be very effective in deterring slugs and snails from consuming lettuce plants. Myrrh essential oil and /raws-P-ocimene were also molluscicidal against the small field slug. Little slug mortality was observed when ethanol extracts of myrrh were employed, whilst still maintaining its strong repellent properties. No incidences of snail mortalities were observed throughout the spray trials. Myrrh and opoponax oleoresins were found to have no toxic effects on earthworms and their 3% extracts showed very little phytotoxic effects against lettuce plants. Traws-p-ocimene (5%) extracts were well tolerated but marginally affected one variety of curly lettuce. This study has shown the novel application of myrrh and opoponax oleoresins, their extracts, and their chemical components in affecting the feeding activity of terrestrial molluscs.

No description available.

Seed germination is one of the most important developmental steps in the life cycle of a higher plant. Because of this, seed producing plants have evolved mechanisms, such as dormancy, that time germination based on environmental cues. The present study uses Arabidopsis thaliana as a model to address questions about seed dormancy and germination. Three different lines of investigation were followed. The first involved an investigation of how light quality regulates phytohormones in order to control germination. This identified a light-dependent mechanism that differentially regulates expression of the ALLENE OXIDE SYNTHASE and OXOPHYTODIENOATE-REDUCTASE 3 genes resulting in accumulation of cis-12-oxo-phytodienoic acid (cis-OPDA) and repression of seed germination under FR conditions. The second line of investigation involved a re- examination of the role of the ABSCISIC ACID INSENSITIVE (ABI) 5 and ABI4 transcription factors in regulating seed germination and oil mobilization respectively. The study found that abscisic acid (ABA) is able to block testa rupture in nicked seeds and this involves the ABI5, but not the ABI4, transcription factor. Furthermore, it was found that ABI4 is involved in the repression of ABA and cis-OPDA biosynthesis in a light- dependent manner, but has only a minor role in regulating oil mobilization in seeds. The third line of investigation focused on the regulation of dormancy during after-ripening and found that changes in phytohormone levels over an extended period can account for changes in dormancy state.

Jatropha curcas is a perennial shrub from the Euphorbiacea family. It is known for its stress resilience and high seed oil content, however little selective breeding has been carried out to fully domesticate this species. The aim of this project is to identify and map quantitative trait loci (QTL) for seed oil content, seed oil composition (oil quality), and oil yield, in order to identify loci suitable for introgression into an economically viable cultivar. In this study, an F2 population (G51xCV) consisting of 229 plants for linkage analysis, and 145 plants for QTL analysis, was used to identify and position 312 genetic markers and 8 quantitative traits onto a genetic linkage and QTL map. Over 288 short sequence repeat (SSR) markers were mined from genome sequence to complement single nucleotide polymorphism (SNP) markers from genomic and transcribed DNA. 132 of the mined SSRs were physically linked to candidate genes, leading to the mapping of a substantial portion of genes that form the seed oil biosynthetic pathway in Jatropha curcas. Integration of phenotypic datasets collected over 2 independent years, enabled the identification of 15 QTL regulating seed oil content (2QTL), seed oil composition; palmitate, stearate, oleate, linoleate content (10 QTL), seed weight (1 QTL), number of branches (1 QTL) and seed yield (1QTL). Combined PVE for these QTL accounted for between 9.34 % (palmitate content year 2) to 32.26 % (seed oil content Year 2) of observed variation. Analysis of final oil yield per plant, showed that seed yield (number of seeds) was most important for regulating oil yield in this mapping population, however seed oil content and seed weight were also important traits, highlighting that selection of both seed oil and vegetative traits are of utmost importance for optimising oil yield in Jatropha curcas.

The aim of the present thesis is to further our knowledge of chloroplast protein import regulation by identifying potential novel regulatory components using the model species Arabidopsis thaliana. A forward genetic screen with the pale chloroplast protein import mutant tic40 uncovered two second-site suppressors (stic1 and stic2). The stic1 muta-tions map to the known thylakoid biogenesis factor ALB4, which suggest a novel genet-ic interaction between chloroplast protein import and thylakoid biogenesis. The genetic interaction between TIC40 and ALB4 is shown to be specific, and the chloroplast pro-tein import defect of tic40 mutants can be suppressed by stic1/alb4 mutants. Further-more, the ALB4 and STIC2 proteins are shown to interact in a common pathway, the abrogation of which leads to deteriorated thylakoid ultrastructure, suggesting that both ALB4 and STIC2 are involved in thylakoid biogenesis. Apart from thylakoid ultrastructural defects, the abrogation of the STIC function leads to the massive induc-tion of an as yet uncharacterized gene, HINAS1, potentially mediated by a hormone sig-nal originating from the chloroplast. How such a signal could indirectly suppress the defects of tic40 mutants is discussed. It is further shown that the alb3 alb4 double mutants are smaller and accumulate less pigments than the alb3 single mutants, and that the chloroplast ultrastructure is further deteriorated in the double mutant compared to alb3. Similarly, the cpftsy mutant and the cpsrp54 cpsrp43 double mutants show also a more severe phenotype in the alb4 back-ground. These findings are backed up by the detection of weak but specific interactions of ALB4 with ALB3 and both cpSRP components, suggesting that the functions of ALB4 and its paralogue ALB3 overlap partially, and that thus both components likely contribute differentially but synergistically to the same process of protein insertion into the thylakoids via the chloroplast signal recognition particle pathway.

Seed germination is critical for plant establishment but little is known about how the reduction-oxidation (redox) environment of the cells in the emerging root meristem influences cell division. The glutathione redox potentials of the nuclei and cytosol were determined using redox-sensitive green fluorescent protein (roGFP2) in the Arabidopsis root apical meristem, in which cell cycle had been synchronised using hydroxyurea, within the period immediately after germination, in order to characterise the relationships between cellular redox status and cell cycle progression. The average glutathione redox potentials of the nuclei and cytosol were -297.5 mV ± 0.7 and -292.8 mV ± 0.6 respectively. However, a transient oxidation occurred in compartments during the G1 phase of the cell cycle, as determined by the expression of cell cycle markers (CYCB1;1-GUS, cytrap and cyclins). The effect of low antioxidant buffering capacity on the gene expression profiles of dry and imbibed seeds as well as the redox potentials of the nuclei and cytosol was determined using the ascorbate deficient vtc2-1 and vtc2-4 mutants. The glutathione redox potentials of the nuclei in the proliferation zone of vtc2-1 radicles expressing roGPF2 were -282.3 mV ± 0.5 and the cytosol was -282.9 mV ± 0.5. These increased levels of oxidation persisted throughout the period of measurement, a feature that was linked to changes in cell cycle progression. The transcriptome profiles of vtc2-1 and vtc2-4 dry seeds compared with that of wild-type seeds revealed large changes in the abundance of transcripts encoding transcription factors, redox components, and proteins involved in cell cycle and secondary metabolism. Fewer differences were shown for the transcriptome profiles of vtc2-1 and vtc2-4 imbibed seeds. Taken together these data show that antioxidant buffering capacity exerts a strong influence on cell cycle progression and gene expression without having marked effects on germination.

No description available.

No description available.