Meiosis is a specialised cell division that results in the formation of four genetically unique haploid daughter cells from one diploid parent cell. This is achieved by one round of DNA replication followed by two rounds of nuclear division. This is in contrast to mitosis, which produces genetically identical diploid daughter cells. Errors during meiosis can result in aneupolidy. In humans, aneuploidy can cause miscarriage and disease such as Patau, Edwards and Down syndromes (trisomies 13, 18 and 21, respectively). Therefore, understanding how meiosis is regulated is of great importance in understanding the causes of aneuploidy and disease in humans. In this thesis, I have used the model organism budding yeast to study how meiosis is regulated in yeast cells, with a view to understanding how meiosis is regulated in human cells. PP2ACdc55 is a highly conserved phosphatase and its role in meiosis was not addressed in any organism before my work. I constructed a meiotic null allele of CDC55 (cdc55-mn) by replacing its promoter with the mitosis-specific PCLB2. By carefully characterising the phenotype of cdc55-mn strains, I showed PP2ACdc55 is crucial for timing the activation of the FEAR network. I have demonstrated that premature activation of FEAR during meiosis (caused by a lack of PP2ACdc55 activity) blocks spindle assembly and nuclear divisions. In cdc55 meiotic null (cdc55-mn) cells, the Cdk-counteracting phosphatase Cdc14 is prematurely released from the nucleolus concomitant with hyperphosphorylation of Net1. I have found that a mutant form of Net1 that lacks 6 of the Cdk phosphorylation sites rescues the meiotic null defect of cdc55-mn cells. Therefore, I have shown that phosphoregulation of Net1 by PP2ACdc55 is essential in order to prevent precocious exit from meiosis I. In my work described in Chapter 4, I isolated mutant alleles of cdc55 that suppressed the spo12Δ dyad phenotype confirming the opposing roles of Net1-phosphorylation by Cdc55 and Spo12 in the FEAR pathway. I also isolated alleles of CDC55 that suppressed the spo11Δ spo12Δ spore lethality. These alleles affected reductional segregation during meiosis I in achiasmate cells but had no effect in wild type cells. Investigating these alleles further might shed insights into mechanisms that work with chiasmata in ensuring efficient monopolar attachment during meiosis I.

Seven study sites within the South Wessex Downs Environmentally Sensitive Area (SWD ESA) were used to evaluate re-created downland turf, a habitat created under one of the scheme management options. The novel habitat was compared to adjacent areas of established downland and to the edges of arable fields, by collecting vegetation data, and using invertebrates as indicators of habitat quality. The recreated downland sites were re-seeded 1 to 3 years before the study. The new habitat was influenced by adjacent established downland and calcicolous species were found colonising the: edges of the re-created downland. The edges of established downland were degraded in terms of plant species richness, probably by previous arable use in adjacent fields. It was found that the re-created downland was being used by several butterfly species for breeding as well as for nectaring and that these activities were concentrated around the edges of the habitat. A second indicator group, the Homoptera, were also found on the re-created downland and, although no evidence of breeding was gathered, some of the species found on the habitat were characteristic of established downland. A third aspect of the study focused on the effect on associated herbivores of the nonnative varieties of downland species which are sown into the re-created downland. It was found that these were not as easily digested as a native variety and that although the larvae gained more weight they pupated later, thus increasing their chances of predation. This has not previously been demonstrated and it is hoped that they will help improve the management of the SWD ESA in future years.

There is increasing concern among restoration ecologists that using non-local propagules in revegetation schemes may influence the success of grassland restoration. This research programme investigated the importance of propagule provenance in restoration schemes. In particular the work focused on two areas. Firstly, the study investigated the significance of propagule provenance for plant establishment and persistence using Lotus corniculatus as a model species. Secondly, it investigated the practical implications of restricting seed procurement to local sources, using a field trial which assessed the success of limestone grassland re-creation under different treatments. Propagules were collected from two contrasting habitats within each of six regions in the British Isles and a common garden experiment was used to quantify the genetic component of provenance as estimated by plant morphology and fitness. There were differences in survival, growth habit, pubescence, leaf shape, plant size and fecundity between plants grown from seeds sourced from different regions. In addition these populations differed in the extent to which they were damaged by seed herbivores. Differences between plants grown from seed sourced from contrasting habitats were limited to morphology. These findings suggested that populations would be likely to perform differentially in a restoration environment. Both geographical location and the ecological conditions at the seed source should be considered when procuring seeds for a restoration scheme. A field trial was set up to establish whether local propagules exhibited higher fitness than those collected from non-local sources. Propagules were collected from two contrasting habitats in each of fifteen regions. Two restoration environments at a single site were investigated; one was treated with a dressing of topsoil, the other site was untreated bare clay substrate. Differences between populations were measured in terms of both geographical and ecological distance. Results for both sites demonstrated that although there was no home-site advantage in terms of geographical distance, plants from more distant populations were smaller and less fecund in the restoration environment. An investigation into the relationship between ecological distance and plant performance produced different results on the treated and untreated plots. On the treated plot there was no significant relationship but on the untreated plot, plants from more distant populations were larger and more fecund. The contrast in the results obtained for the effect of geographical and ecological distance on performance in the untreated restoration environment is interesting. The enhanced performance of geographically local populations agrees with findings from previous studies. The findings for ecological distance are unexpected based on other work. However, it is postulated that the initial success of non-local populations maybe misleading, as environmental conditions which are infrequent but typical of the area may lead to high mortalities in the longterm. The range of what can be considered local is rarely considered in studies that investigate plant provenance, but work from other areas suggests that there is sufficient variation over small distances to warrant seed collection within 100m. Fine scale phenotypic variation over 200m in populations of L. corniculatus was investigated, however there was no evidence to suggest that seed collection should be restricted to 100m, consequently seeds could be safely collected up to 200m from a restoration site. If seed procurement is to be restricted to local seed then it is possible that the seed application rate and species mix available for a restoration project may be limited. A field trial investigating the effect of different treatments showed that it is possible to establish an appropriate plant community using a low sowing rate. However, that community will be more vulnerable to changes in the environment during the establishment phase and more open to invasion by colonizing species which are likely to be weedy in the first few years. A comparison of two seed mixes showed that a diverse seed mix resulted in an increased diversity and evenness of vegetation. There was no benefit in adding a nurse grass to compensate for a low application rate of local species. In conclusion, although it is an advantage to use seeds of local provenance in restoration schemes, it will be necessary to balance this with the likelihood of successful re-vegetation given the seed available

Circadian clocks involve feedback loops that generate rhythmic expression of key genes. Molecular genetic studies in the higher plant Arabidopsis theliene have revealed a complex clock network. We begin by modelling the first part of the Arabidopsis clock network to be identified, a transcriptional feedback loop comprising TIMING OF CAB EXPRESSION 1 (TOCl), LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1). As for many biological systems, there are no experimental values for the parameters in our model, and the data available for parameter fitting is noisy and varied. To tackle this we construct a cost function, which quantifies the agreement between our model and various key experimental features. We then undertake a global search of parameter space, to test whether the proposed circuit can fit the experimental data. Our optimized solution for the Arabidopsis clock model is unable to account for significant experimental data. Thanks to our search of parameter space, we are able to interpret this as a failure of the network architecture. We develop an extended clock model that is based upon a wider range of data and accurately predicts additional experimental results. The model comprises two interlocking feedback loops comparable to those identified experimentally in other circadian systems. We propose that each loop receives input signals from light, and that each loop includes a hypothetical component that had not been explicitly identified. Analysis of the model predicts the properties of these components, including an acute light induction at dawn that is rapidly repressed by LHY and CCAL We find this unexpected regulation in RNA levels of the evening-expressed gene GIGANTEA (GI), supporting our proposed network and making GI a strong candidate for this component. We go on to develop reduced models of the Arabidopsis clock to aid conceptual understanding, and add a further proposed feedback loop to develop a 3-loop model of the circadian clock. This 3-loop model is able to reproduce further key experimental data.

Stomatins belong to the band-7 (or SPFH domain) family (short for Stomatin, Prohibitin, Flotillin HflC/K) of diverse membrane proteins. This protein family is evolutionary conserved with members found in all sequenced eukaryotes and in most prokaryotes. Band-7 family proteins have the ability to oligomerise and generally aid in the assembly and regulation of large membrane-bound protein complexes. In animals, stomatins have been demonstrated to regulate ion channels by direct protein interactions. Additionally, they localise to membrane microdomains where they actively contribute to their assembly by binding sterols, and they also associate with the actin cytoskeleton. The Arabidopsis genome encodes for two structurally similar stomatin-like proteins that are functionally completely unknown yet. They will be referred to as AtSlp1 (for Arabidopsis thaliana stomatin-like protein) and AtSlp2. The aim of this thesis was to provide a detailed characterisation of these two genes on a molecular and functional level. Both proteins are expressed ubiquitously throughout plant development, but they accumulate at particularly high levels in pollen and other metabolically active cells. Phylogenetic analysis reveals that AtSlps are homologous to stomatin-like proteins of type 2. Amongst these, the human stomatin-like protein 2 (HsSlp2) is localised to mitochondria where it participates in large membrane-bound protein complexes and is also involved in the proliferation of cancer cells. Evidence is provided here that demonstrates mitochondrial localisation of both Arabidopsis Slp proteins in vitro and in vivo. On a functional level, mitochondria from an slp1 knockout mutant plant have a decreased mitochondrial membrane potential and increased oxygen consumption rates. This is interpreted as a defect in coupling efficiency and an impairment of the mitochondrial inner membrane integrity. This defect results in a variety of other growth phenotypes that are related to metabolically active tissues and cell types. Knockout plants are delayed in overall growth of shoots and roots and have decreased seed germination rates. Additionally, these plants are less resistant to conditions of high salinity and are less fertile. Overexpression of a protein acting as a putative dominant-negative Slp fragment results in plants with a dwarf phenotype and early onset of leaf senescence. This phenotype correlates with increased levels of reactive oxygen species and altered organelle ultrastructure. Guard cells from these plants in particular have enlarged chloroplasts and are impaired in transpirational control. It is concluded that also in plants, stomatins act together with other band-7 family proteins as parts of large protein complexes that have regulatory roles important for development and stress responses. Their main role is probably to provide membrane scaffolds that affect mitochondrial function and morphology during cell division and in situations of mitochondrial stress.

Seed development in Arabidopsis thaliana, has been studied at several levels. However, little has been done to study the role of sugar metabolism genes in seed pod development in this species. As the fertilized egg progresses to a mature seed, the sugars composition during different stages of the developing changes. These changes are related to metabolic processes in the developing seeds, but also to the activity of sucrose- converting and transporting genes, active at the interphase between the maternal tissue and the endosperm. Sucrose synthase (SUS) is one of these genes; it catalyses the reversible reaction of sucrose breakdown in the presence of UDP to form fructose and UDP-glucose. In this study we looked at glucose, fructose and sucrose concentration at different time points during seed pod development. These changes in sugar concentrations were analysed in both Colombia wild type and WS (Wassilewskija) ecotypes. By comparison of the sugar composition of these ecotypes, and linking these data with phenotypic observations in both ecotypes during development, we are able to comment on the possible role of sugars in seed pod development. Also, the sugar composition of wild type seed pods were compared with those of Atsus mutant seed pods, and possible effects sucrose synthase mutations on the phenotype of the developing Arabidopsis thaliana seeds were analysed. The effect of sucrose synthase knockouts in developing seed pods were studied by comparing biochemical and phenotypic characteristics data of the Atsus mutants within Colombia wild type plants. Salk line plants were screened to identify plants carrying a homozygous insertion for T-DNA in five of the sucrose synthase genes. The developing seed pods of each of the homozygous mutants were characterized biochemically via High-Performance Anion-Exchange Chromatography (HPAEC). Furthermore, seed weight, number of seed per pod, germination rate and the morphological development of the embryo were closely analysed. The study found out that there were some biochemical effects of Atsus knockout mutants, and some phenotypic effects of Atsus knockout mutants on the developing seed pods. However, in general the effects were not as pronounced as those that were seen in maize seed, pea seed and potato tuber as a result of sucrose synthase knockout. The general pattern of glucose, fructose and sucrose were similar to the Colombia wild type, although in mature seed pods the sucrose levels in Atsus1, Atsus2, Atsus3 and Atsus6 were slightly, but significantly lower than in the Colombia wild type.

A number of species of wood decay fungi important for the damage they cause to timber and timber products in Korea were cultured. Trametes versicolor, which is one of the most important, was also cultured from a collection made in the UK and likewise the ascomycete Daldinia concentica was obtained for comparative studies. In the initial testing of the effectiveness of the two wood preservatives, ammoniacal copper quaternary (ACQ) and copper azole (CuAz) preserve injected blocks of Japanese Red Pine and Yellow Poplar were inoculated with T versicolor, Pleurotus ostreatus and D. concentrica. Weight loss(%) of the wood blocks showed that Japanese Red Pine possessed greater natural resistance to decay by the white rot basidiomycete fungus T versicolor, than to the white rot ascomycete D. concentrica. The results for Yellow Poplar were the opposite. It was also found that both preservatives had an inhibitory effect on all three test fungi regardless of tree species. Furthermore ACQ was the most effective preservative in relation to T versicolor, which is the most damaging wood decay fungus in Korea. It has also been found that the absorption of the preservatives by the two different wood types differed with Yellow Poplar exhibiting a slightly greater absorption than the Japanese Red Pine, which might be a result of differences in the anatomical structure of the woods. Fungal biomass was also determined using chitin and ergosterol assays. The results regarding levels of decay caused by T versicolor, P ostreatus and D. concentrica are in close agreement with the weight loss determinations. The assays also confirmed the effectiveness of the copper based preservatives. The application of Scanning Electron Microscopy (SEM) has allowed observations on the damage caused by the test fungi to the untreated blocks of the two wood species and the reduction in damage on blocks treated with the preservatives. Linked studies using the SEM and Atomic Force Microscopy have demonstrated differences in the micromorphology of the hyphal tips of the test fungi.

A study of the properties of tree-ring density and ring-width chronologies from five sites in the British Isles, two in Sweden and two sub-fossil sites in Northern Ireland is described. The technique of x-ray densitometry is used to measure density. It is shown that it is possible to use x-ray densitometry on well preserved sub-fossil pine. Chronologies have been constructed for parameters of earlywood and latewood widths, ring-width, maximum and minimum densities for all sites. The statistical properties of chronologies are related to the latitude and altitude of the sites. Sub-fossil chronologies behave differently to any of the living tree chronologies. Response functions on monthly temperature and precipitation data are calculated for the five tree-ring parameters for the living tree chronologies. A principal component analysis involving 25 ring-width chronologies from northwestern Europe is used to examine the spatial relationship between British and European ring-width chronologies. The continuous pattern of density variation across the annual ring is measured for trees from two scottish sites, at Glen Derry and Glen Affric from 1900 to 1979. A method of constructing and comparing annual density profiles by fitting cubic spline functions to the density data is described. This has enabled the effects of growing season climate on density to be examined. The importance of temperature in governing tree-ring density is demonstrated. The use of image analysis techniques to measure the continuous variation in cell dimensions across the annual ring is described. Variations in ring density are explained in terms of changes in wall thickness and lumen diameter. A comprehensive literature review on the physiological mechanisms controlling the response of tree-ring width and density in P. sylvestris to climate is described. The physiological causes-for the climate-growth response in earlywood and latewood widths and densities are summarised seperately. It has been possible to explain some of the results of the response function analysis and the density profile study in terms of physiological processes.

Plants are sessile photo-autotrophic organisms and need to adapt constantly to a dynamic environment. Light is of utmost importance for plants to be able to monitor their surroundings. Ultraviolet-B radiation (UV-B; 280-315 nm) is an intrinsic part of sunlight and, depending on the wavelength and the fluence rate, it may be a stressful signal or an “informational” one. The so called photomorphogenic responses of plants to UV-B are largely mediated by the UV-B specific photoreceptor UV RESISTANCE LOCUS 8 (UVR8), which “senses” UV-B via a tryptophan based mechanism. UVR8 is localised in the cytoplasm and the nucleus mainly as a homodimer. Upon UV-B irradiation it splits to its monomers and accumulates in the nucleus where it has been found to interact with the E3 Ubiquitin ligase COP1. In the nucleus UVR8 has been shown to associate with chromatin on loci of UV-B responsive genes, including that encoding for the bZIP transcription factor (TF) ELONGATED HYPOCOTYL 5 (HY5), a key effector of UVR8-dependent signalling pathways. The binding of UVR8 to chromatin appears to take place via interaction with histones (H2B in particular) rather than DNA itself. However, this association with chromatin seems not to be UV-B specific. The above data suggest a mechanistic basis for an assumed function of UVR8 in the regulation transcription. It seems likely that UVR8 interacts with other proteins associated with chromatin to promote remodelling and/or recruits/activates TFs which in turn stimulate transcription of its target genes. The main objective of this study was to address the above working hypothesis.

Dimethylsulphoniopropionate (DMSP) is a dimethylated sulphur compound that appears to be produced by most marine algae and is a major component of the marine sulphur cycle. The majority of research to date has focused on the production of DMSP and its major breakdown product, the climatically important gas dimethylsulphide (DMS) (collectively DMS/P), by phytoplankton in the open ocean. A number of functions for intracellular DMSP (DMSPi) in phytoplankton have been identified and the cycling of DMS/P appears to be critical for ecosystem function. However, mechanisms for the production and release of DMS/P in the coastal ocean are poorly understood, despite the region’s economic and ecological importance. Coralline algal habitats (e.g. maerl beds, coral reefs, seagrass meadows, kelp forests) are distributed throughout the coastal oceans worldwide. Their three-dimensional structure supports high biodiversity and provides numerous services, generating considerable economic wealth. DMSPi in coralline algae is known to be high, thus coralline algal habitats may be critical components of the coastal sulphur cycle. This research aimed to improve our understanding of the production of DMS/P by coralline algal habitats by investigating (1) natural spatiotemporal variation and (2) the influence of environmental pressures. This was achieved through a number of laboratory and field-based studies, utilising modern and well-established techniques. The first objective of this research was to better understand the photosynthesis of red coralline algae (Chapter 3), as the algal precursor to DMSPi is methionine, a product of photosynthesis. The photosynthetic characteristics of coralline algae exhibited acclimation to changing light conditions (e.g. over a diurnal cycle or between natural and static lighting conditions). Further, for the species tested, coralline algae are often subjected to light-saturating natural conditions, therefore requiring efficient photo-protective mechanisms, which may include DMSPi regulation. On a global scale, DMSPi in coralline algae may decline with latitude, reinforcing the role of DMSPi as an antioxidant (Chapter 4). At smaller spatial scales, DMS/P production, release and recycling mechanisms were apparent in a number of habitat types (Chapter 4). A strong seasonal trend in DMS/P was also observed at a Scottish maerl bed, driven by water temperature and cloud cover (Chapter 5). Annually averaged DMS and DMSP concentrations were 230% and 700% respectively higher than the open ocean, highlighting the potential importance of the coastal ocean in the marine sulphur cycle (Chapter 5). The influence of environmental pressures (decreased salinity, variable pH and grazing) on DMS/P production by coralline algal habitats was examined (Chapters 6 – 8). In agreement with the phytoplankton literature, a chronic, but not acute, reduction in salinity led to a significant decline in coralline algal DMSPi concentrations and a sinking of the surface epithelial cells but no apparent impact on photosynthesis (Chapter 6). In the naturally variable tropical reef environment, calcifying algae continually regulated DMSPi concentrations in response to the diurnal cycling of carbonate saturation state (Chapter 7), suggesting that DMSPi may be enhanced under low pH regimes to compensate for enhanced oxidant production. Under low pH conditions, cracks were observed between the surface epithelial cells of coralline algae, potentially allowing DMSPi to leak from the cells (Chapter 7). In the field, grazing by urchins appeared to facilitate the release of DMS/P from kelp in coralline algal habitats (Chapter 8). In the laboratory, DMSPi in coralline algae increased in response to chemical cues from grazers rather than direct grazing activity, as had been previously proposed. Prior to this research, little information was available on DMS/P concentrations in coralline algal habitats. The marine sulphur cycle may impact climate regulation and ecosystem function on a global scale. This research provides a comprehensive source of information on the importance of coralline algal habitats in the marine sulphur cycle by examining natural variability and potential changes in response to environmental perturbations. This work will form a baseline for continued research in this field, investigating, for example, the impact of multiple stressors on DMS/P production, release and recycling in coastal marine habitats.