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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.

Environmental studies of the genus Rosa

Khosh-Khui, Morteza January 1975 (has links)
Experiments were conducted to investigate the effects of intensity, duration, quality and timing of light on the glasshouse rose (Rosa hybrida L. cv. Baccara). Effects of treatments were studied on flower yield, quality and index; blind shoots; abnormal flowers; days to flowering; stems remaining on the plants; stem length; node number; average internode length; neck node length; leaves and leaflets number; stem diameter; terminal leaflet area; petal size; petal number; fresh and dry weight. Data presented, indicated that production of Baccara in South West England followed solar energy curve; the highest yield obtained after receiving the most natural light in vegetative growth phase. Lighting increased flower yields and decreased blind shoots, especially in limited natural light periods of the year, proportionately to the quantity of light received by the plants; intensity being more effective than duration. Bottom breaks and axillary shoots developments were stimulated Dy lighting; the latter was more responsible for higlier yields. Lighting promoted earlier flowering mostly proportional to light intensity. Night break with high pressure mercury lamps increased flower yield significantly and decreased the days to flower non significantly. Cyclic lighting with low light intensity of incandescent lamps did not affect the roses. Overall results suggested that Baccara rose might be classified as a day neutral plant under the condition of this investigation. High pressure sodium lamps proved to be an efficient light source for rose supplementary lighting. Supplementary lighting was more effective when it was provided in vegetative than reproductive growth phase. Generally all the recorded characters improved under light but on average the differences were non significant. However, node number remained almost unchanged and neck node was shorter under higher light intensity and duration. Significant correlation coefficients were demonstrated between some characters of cut stems which were independent of stem nature, seasons and light treatments.

Developing Arabidopsis thaliana as a model for use in conservation genetics

Priest, Anne January 2014 (has links)
Conservation genetics is the application of evolutionary and molecular genetics to the conservation of biodiversity. It can also be seen as a way to minimize the harmful effects of human activities by managing the evolutionary process and maintaining the adaptive potential of natural populations. In the past twenty years the field of molecular biology has advanced with leaps and bounds, providing the necessary tools for the use of genetics in conservation. Arabidopsis thaliana is a model organism that can help us understand how future plant populations will respond to environmental changes. The three studies presented here use A. thaliana as a model system to gain a more complete understanding of how early flowering can affect development; to gain insight into the traits that may indicate tolerance to water stress; and finally, to shed light on how hybridization and previous selection can affect a populations’ adaptive potential. I found that early flowering does impact plant development. Plants that flowered earlier had a slower rate of leaf initiation, less leaves and smaller rosettes. I found that although the majority of plants produced less fruits in a water-limited environment, there were some individuals that produced a greater number of fruits under water stress. There is a strong selection to decrease the number of days to first flower in water-limited environments. I found that plants that had previously undergone a strong selection for early flowering were initially more tolerant to drought than unselected plants but the advantage was lost after three generations of a selection for drought tolerance. There was heterogeneity in the response to the selection amongst the hybrid populations. The information we gain by using A. thaliana can be extrapolated and applied to species that are threatened in order to better understand their evolutionary processes.

Taxonomic problems in the genus Cerastium : being a biometric study of the variation of four annual species of Cerastium together with certain field observations and a discussion thereof

Whitehead, F. E. January 1952 (has links)
No description available.

Alkaloids of Picralima nitida Stapf, TH. and H. Durand

Thomas, Alan Francis January 1954 (has links)
No description available.

Dissecting the role of the response regulator SAC29 in Brassica species

Snell, Chelsea January 2017 (has links)
Response regulators (RRs) are crucial signalling components that allow plants to respond to fluctuations in their environment. ARR22 is a unique type-C RR previously identified in Arabidopsis that is hypothesised to be post-transcriptionally up-regulated in response to wounding at the seed:funiculus junction and hence has a predicted role in assimilate partitioning. A putative orthologue known as SAC29 has been isolated in the economically important allotetraploid crop Brassica napus (B. napus). A total of 83 putative RRs in B. napus (BnRRs) have been identified which can be classified into type-A, -B and –C RRs comparable to Arabidopsis. A subset of putative type-A and type-B BnRRs were examined further and expression was detected in early seed development stages which may reveal novel functions for these genes in B. napus. In silico and expression analyses have identified and characterised four putative ARR22 orthologues (BnRR76 – BnRR79) that exhibit 81.25% amino acid similarity. Distinct differences in nucleotide and amino acid sequence were observed in BnRR76 and BnRR78 that originate from B. rapa and B. oleracea parental genomes respectively. All genes contain two introns, one located within the 5’UTR and one in the ORF, similar to ARR22. RT-PCR analysis revealed differences in spatial and temporal expression of BnRR76 and BnRR79 during seed development. Retention of an intron located within the open reading frame in BnRR77 and BnRR79 was also observed at different stages of seed maturation. Mechanical wounding of seeds did not elicit a change in seed storage protein or cysteine protease expression even after 120 mins and hence does not support the hypothesis that putative B. napus orthologues of ARR22 are necessarily involved in assimilate partitioning. An antibody was designed to recognise an amino acid sequence present in ARR22, and BnRR76 – BnRR79, and was subsequently used in Western blot analysis. Expression of BnRR76 – BnRR79 proteins in seeds was rapidly up-regulated at 60 mins post-wounding while gene expression levels remained at a baseline level until 120 mins when protein level decreased suggesting that a rapid wound response occurs at the protein level rather than at the level of gene expression. Using a dexamethasone (DEX) inducible system, physiological effects of ARR22 overexpression were elucidated. DEX-induced overexpression resulted in severe phenotypes comparable to cytokinin receptor mutants such as reduced rosette area and stunted inflorescence. Transgenic lines in which a predicted phosphorylation site, hypothesised to be critical for protein function during stress response, had been mutated exhibited comparable phenotypic effects and hence suggests a possible different mode of mechanism of ARR22 when ectopically expressed. This project explores and characterises response regulators, with particular focus on their involvement in seed development, for the first time in the economically important oilseed crop B. napus. Future work should examine wounding effects at longer time points as well as aim to elucidate downstream components and targets of ARR22 and its putative B. napus orthologues BnRR76 – BnRR79.

Taxonomic and ecological studies in the Genus Gentianella

Pritchard, N. M. January 1957 (has links)
No description available.

Determinants of Seedling Recruitment in Mimosa Pigra L

Mansor, Asyraf January 2008 (has links)
Mimosa pigra L., a semi-aquatic woody legume, is a well known invasive plant in the tropics. Originating from Latin America, this species has spread to various localities around the globe and caused serious problems, both environmental and economical, in its new environment. I carried out a survey to assess the current status of Mimosa infestation in Peninsula Malaysia. Manipulative field experiments on the effect of soil disturbance, competitor identities, sown seed densities and defoliation on Mimosa seedling recruitment and survival were conducted as well. I found that although disturbance may not be an essential factor for seedling emergence in Mimosa, it significantly increase seedling establishment and survival. Recruitment in Mimosa was negatively affected when seedlings were grown together with vine (Centrosema) and creeper (Ipomoea), suggesting the importance of interspecific competition in reducing seedling emergence and establishment. The seed-sowing treatment showed that recruitment in Mimosa was both seed-limited and microsite-limited. While the number of seedlings emerging increased with the density of sown seeds, the proportion of emergence remained constant across the sown seed densities. Herbivory (through artificial defoliation) reduced seedling survival in Mimosa, although some seedlings proved to be resilient to even the highest intensity and frequency of defoliation. In general, I argued that Mimosa invasion in Peninsula Malaysia is not a serious problem since its populations were mostly restricted to disturbed ground and abandoned land. I would like to suggest that current best course of option is to continue monitoring its population and evaluate its spread, as control of established stands without destruction of the seed bank is likely to cause insignificant impact on subsequent population. One recommendation is to restrict the movement of topsoil from Mimosa infested sites. Future researches, if they were to be conducted shoUld try to establish method(s) that will reduce the Mimosa seed bank.

Natural Variation in the Vernalization Response of Arabidopsis thaliana

Strange, Amy January 2008 (has links)
Within Arabidopsis thaliana there is extensive natural variation in the timing of flowering. This thesis focuses on the variation in vernalization response, manifested as a requirement for different lengths of cold in order to fully accelerate flowering. During vernalization, the gene encoding the floral repressor FLC is silenced and this is maintained during subsequent development by a Polycomb-mediated chromatin silencing mechanism. Three accessions from Sweden (Lov-I, Ull-2-5 and Var-2-6) require extended vernalization due to a slower accumulation ofthe chromatin silencing during the cold. In this study a QTL analysis mapped the variation in vernalization response to chromosomes 1,4 and 5. Further fine mapping identified FLC as one ofthe loci underlying the QTL and polymorphisms in FLC were located in putative regulatory rather than protein-coding regions. Allelic variation in FLC was found to be directly responsible for variation in the stability ofFLC repression after short lengths of vernalization. Work is ongoing to map the nucleotide polymorphisms which are directly responsible for the phenotypic variation. The vernalization response of two accessions from America (Kno-I8 and RRS-IO) was also investigated. They express FLC at extremely low levels, but are late flowering. Vernalization response QTL in these accessions again mapped to chromosomes 1,4 and 5. Low FLC expression was associated with a transposable element insertion in intron 1 ofFLC. Cloning of this transposon into a wild-type FLC allele showed it inactivates function and demonstrated modifiers in the American accessions that result in their late flowering. Initial results are described from a European common garden experiment, addressing whether flowering time is an adaptive trait. It was found that the Swedish accessions described above have low fitness in non-vernalizing conditions.

Properties and applications of pathogen effector proteins in Arabidopsis thaliana

Sohn, Kee Hoon January 2008 (has links)
Plants activate innate immune responses upon pathogen invasion. However, successful pathogens overcome host immunity and cause disease. Pathogen effector proteins play critical roles in suppressing host immune responses and modulate the properties of the host environments to favor pathogen reproduction. A bacterial T3S effector, AvrRPS4, from Pseudomonas syringae has been widely used to study plant immune responses. However, the properties and functions are unclear. The avirulence and virulence activities of AvrRPS4 during bacterial pathogenesis in Arabidopsis were investigated. The processing of AvrRPS4 is required for virulence activity but not for avirulence. Transgenic plants expressing AvrRPS4 from a weak promoter in the absence of RPS4 showed enhanced Pst DC3000 growth and suppressed PTI phenotypes. The mechanism involved in the processing of AvrRPS4 seems to be conserved in the Xanthomonas effector, XopO. To develop a high throughput assay system to study the effectors from an biotroph oomycete pathogen, Hyaloperonospora arabidopsidis, AvrRPS4 was used to create T3SS-based delivery effector system. Using this method, I showed the virulence activities of H. arabidopsidis effector ATR13 and found novel resistance triggered by specific alleles of ATR13 in Arabidopsis accession Ws-O. Little is known how pathogen effectors suppress plant ETI. Using a mixed inoculation method, ETI-suppressing activities were identified from several Pseudomonas syringae strains. Most significantly, Pph effector, AvrB4, was identified as a suppressor of AvrRPS4-triggered HR. AvrB4 also showed avirulence activity in tobacco. However, AvrB family T3SEs show overlapping and distinct effector functions depending on host plants tested.

Phylogenetic studies in the genus Saxifraga (Saxifragaceae)

Zhang, Zhuoxin January 2013 (has links)
Saxifraga L., the largest genus (ca. 460 spp.) in the family Saxifragaceae, is widely distributed across Europe and Asia, mainly in the Alps and the Sino-Himalayan area, with extensions in the Rocky Mt / Andean Cordillera south to Tierra del Fuego. The genus displays remarkable morphological variation. Phylogenetic analyses were conducted to test previous classifications. Molecular evidence comprised DNA sequences from the chloroplast gene (matK) and nuclear regions (ITS and Duo1). The sequences were also used in plant identification. In many cases genetic distances between species in terms of DNA sequences were very low, indicating rapid evolution. Morphological evidence, including microscopic characters from pollen nuclear number, exine and leaf venation, was also collected. Phylogenetic trees were produced from the molecular data, the morphological data and from the combined data. Morphological data improved resolution in the molecular trees. The phylogenies were in substantial agreement and suggested that a few taxonomic realignments and new combinations are needed to make the sections and subsections monophyletic. A revised classification of Saxifraga primarily to subsection level is presented. The main changes from previous classifications are: (1) genus Saxifragella is included as a monotypic section in Saxifraga; (2) sect. Ciliatae subsect. Serpyllifoliae is merged into sect. Ciliatae subsect. Rosulares; (3) sect. Ciliatae subsect. Cinerascentes is merged with subsection Gemmiparae; (4) section Porphyrion is monophyletic only if S.mutata and S. florulenta (formerly in sect. Ligulatae) are included; this transfer also makes sect. Ligulatae monophyletic; (5) S.mutata and S.aizoides (the later formerly in sect. Xanthizoon) are closely related and are now placed together in ser. Xanthizoon of sect. Porphyrion. The geographical distributions of the basal sections of the genus, i.e. Irregulares, Heterisia, Saxifragella and Trachyphyllum suggest an origin of the genus around the shores of the Pacific Ocean, probably in the Beringian area.

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