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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Expression and functional characterisation of genes putatively involved in freezing tolerance in Arctic species of Vaccinium

Oakenfull, Rachael Janet January 2014 (has links)
Freezing temperatures are responsible for destroying vast areas of crops globally each year and are a major factor in explaining the size and distribution of plants. The ability of plants to survive freezing events, depends on predictable and gradual lowering of temperatures, allowing cold acclimation to occur before freezing temperatures arrive. Climate change is altering maximum and minimum temperatures globally and, making freezing events less predictable. A further understanding of the molecular mechanisms of acquired freezing tolerance would give insights into potential genetic targets for crop improvement. In Arabidopsis, CBF/DREB1 transcription factors are currently the most well characterised proteins associated with acquired freezing-tolerance. Studies were performed on three species of Vaccinium collected from the Arctic, V. myrtillus, V. uliginosum and V. vitis-idaea. Genes encoding CBF/DREB1 transcription factors from each of these Arctic species were isolated, sequenced and expressed in Arabidopsis. Characterisation studies were performed on transgenic lines generated from each of the three Vaccinium species. Induced COR gene expression, freezing tolerance and altered phenotype were measured in these lines. Results showed that V. myrtillus CBF/DREB1 can induce freezing tolerance in Arabidopsis. Western blot and reporter gene assay analysis of transiently-expressed CBF/DREB1 from Vaccinium, highlighted the possibility that the CBF/DREB1 from V. uliginosum was less stable than the CBF/DREB1 from the other two species. Site-directed mutagenesis of five regions of interest between the three Vaccinium species showed that the substitution of two amino acids improved COR gene binding/induction. This substitution could serve as a potential crop improvement site for commercial blueberry crops (V. corymbosum). Other genes associated with the CBF/DREB1 pathway in Arabidopsis were cloned and sequenced from the three Vaccinium species. Cold-induced expression of these genes was tested and showed similarities in sequence and expression pattern between V. vitis-idaea and Arabidopsis.

Succession and homeostasis in heath vegetation

Legg, Colin J. January 1978 (has links)
The development of an Arctostaphyleto-Callunetum community following fire was studied in stands up to 40 years old on the Muir of Dinnet, Aberdeenshire, Five phases in the development of 'the vegetation were recognized and designated the initial, pioneer, building, mature, and degenerate phases. Plant species were classified according to the time in the succession at which they were most abundant,. The major classes were: a) species abundant in the initial phase but absent or rare in later phases; b) species which occurred throughout the succession though sometimes not fully developed in the initial phase; c) species occurring only in the nature and degenerate phases, The behaviour of each species was found to be related to its morphology and habitat requirements. The diversity of the community decreased from the initial to the mature phase, reflecting the build-up in dominance of Calluna and Hypnum cupressiforme in the shrub and ground strata respectively. An increase in species evenness and diversity occurred in the degenerate phase where the Calluna had become degenerate , and the. dominance was shared by Erica cinerea, Arctostaphylos uva-ursi, Pleurozium schreberi and Hylocomium splendens to form a mosaic in the vegetation Each of the species studied showed a different strategy of production of underground perennating organs, or of seed production, distribution and dormancy which enabled it to survive a fire or re-establish itself in the community, 6. Seeds of several native heathland and non-heathland species were introduced into stands of heath vegetation of different ages since burning, and also into stands disturbed by removing successive strata of the vegetation. Germination and survival were monitored over two growing seasons, 7. Seed germination and establishment in closed vegetation was very low: the maximum survival observed over two growing seasons was 3.4% of total Sarothamnus scoparius seeds planted in pioneer-phase plots. Establishment from seed is therefore of little significance in the post-fire succession except during the first few years following the fire, or when considered over a much longer time period as in succession to woodland, 8. The germination and establishment of each species introduced to the vegetation showed a unique response to communities of different ages, and to disturbed communities, 9. The soil surface structure and layer of lichens in the pioneer-phase vegetation, and the mat of mosses in the mature-phase vegetation were as significant in producing a micro-habitat unsuitable for the germination of seeds as 'the shrub layer. The shrub canopy may, under certain circumstances, protect young seedlings from grazing and extreme drought, 10, The succession was recognized as passing through two phases; first, the establishment of plants from seed or from surviving stem, bases, and the vegetative spread to fill the space available thus forming a mosaic, each patch dominated by . one Cor more) species; and second, the competitive interaction between neighbouring patches and the local replacement of one dominant by another, 11, A model was constructed of vegetation change as a Markovian process of plant-by-plant replacement, Each patch in the vegetation was recognized as being in one of 15 possible ''states" defined by the dominant species, A transition probability matrix for the 15 states was obtained from field observations and applied in a matrix model to predict the pattern of vegetation development, 12, It was found that the transition probabilities for states containing Calluna as dominant or co-dominant changed as a function of the age of the plant. This factor was incorporated as a step function in the model, a different transition matrix being used for patches in which the dominance of Calluna had been maintained for a certain number of generations of the model. This model gave good agreement with the observed proportions of dominants at different stages of the succession, 13, The model quantifies the results of interaction between each species and its neighbours and illustrates the uniqueness of the response of each species and the complexity of the system, 14, The overall picture of post. fire succession helps to explainthe co-existence of many species in a dynamic, yet stable system through the complementary life-strategies of plants, In a successional community the plant niches are separated in time as well as in space and habitat requirements.

The development of chloroplast membranes and of the lamellar proteins in Phaseolus vulgaris L

De Montes, Ana Herrera January 1977 (has links)
No description available.

Relicts, refugia and reticulation : a study of population history, hybrids and phylogeny in the long-lived flowering tree genus Tilia

Phuekvilai, Prattana January 2014 (has links)
Tilia L. (lime or basswood) is a genus of large trees that are widely distributed in the temperate regions of the Northern Hemisphere. Tilia is an under-investigated genus with unknown species relationships. Therefore, a phylogeny of the genus was reconstructed. This revealed disagreement of the phylogenetic placement of some species and also indicated extensive hybridization. To investigate this further, the most tractable and widely distributed species across Europe, T. cordata (Mill.) or small leaved lime and T. platyphyllos (Scop.) or large leaved lime, were selected for study. This study aims to increase the understanding of genetic diversity and hybridization between the two Tilia species. Also, to gain insight into postglacial recolonization in Tilia across Europe, the patterns of population genetic structure were investigated. In order to achieve the goals, 15 microsatellite markers were developed for detailed genetic analysis. These loci clearly discriminated the two Tilia species. Cross-amplification results indicated that twelve microsatellite markers amplified polymorphic loci in 24 species in the genus. A high level of polymorphism was observed in twenty-five populations of T. cordata and 15 populations of T. platyphyllos from natural woods across Europe. The level of genetic diversity in T. platyphyllos is higher than in T. cordata. Both microsatellite and morphological analysis revealed that natural hybridisation and introgression have occurred between T. cordata and T. platyphyllos in sympatric UK populations, which could be of importance for adaptation and other evolutionary processes. The partial congruence of molecular and morphological analysis suggests that molecular markers are more reliable than morphological analysis for detecting hybridization. The stronger genetic structure observed in T. platyphyllos than in T. cordata suggested that the migration and colonization in the northern areas of T. cordata occurred before those of T. platyphyllos. Microsatellite analysis suggested different possible colonization routes between the two Tilia species. However, T. cordata and T. platyphyllos seem to share the three main refugia in southern Europe (Iberia, Italy and the Balkans). In addition, T. cordata seems to have additional putative refugia in eastern areas. The haplotype network and some shared haplotypes of eight chloroplast regions indicate incomplete lineage sorting rather than recent hybridization.

Phylogenetic studies in the gesneriaceae : anatomical investigations into the relationships of certain genera of the tribe didymocarpeae

Sahasrabudhe, Saroj January 1970 (has links)
The present work is a detailed investigation of the comparative and developmental anatomy of about 110 species belonging to eleven genera of the tribe Didymocarpeae (Gesneriaoeae). The selected genera are representatives of three geographical areas : Asia, Africa and Southern Europe.

An assessment of the suitability of Saintpaulia for genetic manipulations

Bilkey, P. C. January 1981 (has links)
No description available.

Histological studies in the genus Antirrhinum : the significance of histological characters in the taxonomy of European species of Antirrhinum (Scrophulariaceae)

Doaigey, Abullah Rasheed January 1977 (has links)
No description available.

Assembly and annotation of sequences surrounding the S locus in Primula vulgaris

Smith, Matthew Charles January 2015 (has links)
Since Clusius first documented floral heteromorphy in Primula in the 16th century, the genus has been a model system for those studying the development of different floral morphs on plants of the same species. Over the centuries, eminent botanist and geneticists, including Darwin, Hildebrand and Ernst, have furthered our understanding of the phenomenon in a number of species. In Primula vulgaris (Common Primrose), in which flowers take either a long styled (Pin) or short-styled (Thrum) form, heteromorphy is linked to a sporophytic self-incompatibility system, with both mechanisms under the control of the highly conserved, diallelic Self-Incompatibility (S) locus. Whilst classical genetic approaches have identified basic functions of the S locus, as well as the order of the loci controlling these features within the locus, the molecular structure of this important region of the genome remains unknown. Recently, a number of molecular S-linked markers have been characterised, providing an opportunity to begin molecular characterisation of the locus as well as its immediate surroundings. Using these markers as a guide, a single contiguous sequence has been assembled to join three of these markers together, spanning the region in which the mechanisms preventing recombination within the locus breaks down. Within this region, 51 genes have been identified and annotated. Homologues of these genes have been identified in Solanum lycopersicum, Oryza sativa and Arabidopsis thaliana, providing an insight into the convergence and divergence of genes between the four species.

The evolutionary potential of the cowslip Primula veris across a network of nature reserve sites

Bickler, Charlotte April January 2016 (has links)
Anthropogenic environmental change is creating new selection pressures on species' and resulting in extinction, migration and evolution within populations. The potential for evolution on ecological time scales provides opportunity for population persistence, and for stabilising ecological networks affected by biodiversity loss. On the other hand, variation in species' responses may contribute towards mismatch in ecological networks. Understanding the genetic and ecological parameters which promote or limit adaptation will improve our ability to predict species' responses to environmental change. Conservation management must focus on preserving ecological and evolutionary processes in an increasingly modified and changing UK landscape, rather than on protecting static patterns. The Wildlife Trust's 'Living Landscapes' project aims to prevent isolation and inbreeding in populations and maintain ecological interactions, improving species' ability to tolerate environmental change. In this project I explore the evolutionary potential of a key grassland plant species: the cowslip Primula veris. P. veris is an early-flowering obligate outbreeder, fully dependent on foraging insects for sexual reproduction. Through a combination of molecular genetic analysis, field observations, common garden and field experiments; phenotypic and genetic variation in P. veris populations across Wildlife Trust nature reserves is quantified and the relationship between genetic and environmental factors explored. Neutral molecular markers show that the distribution of genetic diversity is spatially variable, and the extent of isolation and differentiation varies across the landscape. Further to this, plastic responses to fine-scale differences in environmental factors are found to play an important role in determining the distribution of phenotypic variance in P. veris quantitative traits. More predictable ecological gradients across a larger spatial scale are likely to drive selection and local adaptation between sites. A complex interplay between genes and the environment is nonetheless revealed with variation in response from site to site, and trait to trait. Ecological trade-offs are predicted to be a determinant of these patterns. Finally, the impact of the observed heritable variation on plant fitness is tested in the field. This highlights the potentially buffering role that the extensive phenotypic variation observed may play, but also the potential cost of mismatch in biotic interactions. Overall, the thesis highlights that the conservation of P. veris' insect pollinators is key to maintaining healthy populations of the species and their evolutionary potential.

Early effects of phosphorous deprivation on the transport physiology, water relations and nitrogen metabolism in Macroptilium atropurpureum cv. siratro

Wahab, Zakaria bin January 1995 (has links)
No description available.

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