Despite widespread conservation efforts, global heathland area has substantially decreased in recent decades. Heathland habitats require low nitrogen availability in order to persist. Over the past 150 years, however, nitrogen deposition has increased markedly. Early observational studies and research using artificial N applications have identified N deposition as the primary driver of heathland succession into grassland or woodland, and N enrichment is considered a threat to heathland sustainability. This study investigated soil fertility and vegetation composition at 25 lowland heathland sites in low rainfall regions of mainland Britain within a modelled wet N deposition range of 1.85 to 10.90 kg N ha-1 y-1. A bioassay approach was used to quantify relationships between soil fertility and N deposition, heathland patch size and the management regimes. This study discovered significant positive relationships between N enrichment and C. vulgaris shoot mass, N and P concentrations. No relationship between N enrichment and N : P mass ratio was found suggesting no N induced shift to P limitation. It was determined that soil phosphomonoesterase activity was not up-regulated in response to N enrichment. This suggests that the soil P reserves are sufficient to satisfy demand under current N deposition loads. Heathland patch size was negatively related to C .vulgaris shoot dry-mass which was used as a proxy for soil fertility. Measured atmospheric ammonia concentrations were not related to C. vulgaris growth and shoot chemistry. No relationships were found between any variable tested and heathland vegetation composition suggesting that local factors, such as management intervention, may be substantial determinants of vegetation composition. This study presents relationships between temperature at origin and C. vulgaris growth from populations located along a latitudinal gradient in Western Europe. The findings of this thesis have implications for current heathland management, and for future management under a climate change scenario.

Radiocaesium (134Cs, 137Cs) is of environmental concern because of its incorporation into the food chain and prolonged emission of harmful radiation. Plants take up caesium via cation transporters which cannot discriminate between radioactive and stable caesium (133Cs). Around 80% of angiosperms live in symbiosis with arbuscular mycorrhizal (AM) fungi that deliver mineral nutrients to their hosts. Contrasting effects of AM fungi on caesium accumulation by plants have been reported. The ultimate aim of this thesis was to determine whether AM fungi reduced caesium accumulation in Medicago truncatula by down regulating the expression of plant genes encoding specific potassium transporters through improving potassium nutrition of their hosts. Accumulation of potassium and stable caesium by non mycorrhizal and mycorrhizal Medicago truncatula was studied, and the effects of caesium and AM fungi on plant gene expression were investigated. In these experiments, shoot potassium concentrations of non mycorrhizal and mycorrhizal plants were identical. However, in some experiments AM associations decreased shoot caesium concentrations. These observations were also true for five other plant species studied. Colonisation of Medicago truncatula with Glomus sp. influenced expression of some genes encoding cation transport proteins, but the expression profile did not suggest improved potassium nutrition. The presence of caesium also affected the expression of several putative cation transporters, but the consequences of these changes are unknown. A reduced colonisation rate of Medicago truncatula by Glomus intraradices was observed at caesium concentrations that exist in the rhizosphere. In conclusion, in these experiments, AM fungi did not improve plant potassium nutrition, and there was no evidence that AM fungi reduced caesium accumulation by down regulating expression of plant genes encoding potassium transporters. Although colonisation by AM fungi can reduce shoot caesium concentrations, this was not always observed. Thus, fungal inoculation cannot be relied upon to deliver crops with reduced radiocaesium concentrations.

Hawaiian Skirt (HWS) is an F-box gene in Arabidopsis that plays a key role in plant floral organ development. HWS has been identified due to sepal fusion along their basal margins resulting in failure to shed its floral organs (Gonzalez-Carranza et al., 2007). Similar phenotypic characteristics can be seen in the ectopically expressed microRNA miR164 (Mallory et al., 2004; Lauf et al., 2004) and in the double mutants cup-shaped cotyledon 1 cucJ/cuc2 (Aida et at., 1997). Previous studies carried out by Gonzalez-Carranza et al. (unpublished) using genetic crosses between hws-1 and other floral mutants has revealed that HWS may play a crucial role in the microRNA biogenesis. In an effort to identify potential substrates of HWS and to identify the role of HWS in the miRNA pathway, a population of EMS mutagenized hws-1 was used for isolation and characterization of suppressors of hws-l. Screening a number of EMS mutagenized hws-l populations has identified several suppressor lines that are currently under study. From the identified mutants, two lines 43.1 and 80.5 were selected for further characterization analysis. These suppressor lines rescue the distinctive sepal fusion phenotype of hws-l as well as displaying other phenotypic characteristics. Characterization of the suppressor lines has identified that 43.1 is an allele of HST gene, which is involved in miRNA biogenesis, and 80.5 is an allele of AS2 gene, which is an adaxial cell fate determinant. Expression analyses have revealed that loss of HWS gene function leads to the repression of both 43.1 and 80.5. Genetic analyses have also confirmed that loss of HWS gene function results in an upregulation of CUC1 and CUC2 gene expression. The results obtained in this project have shown that HWS is involved in miRNA, adaxial-abaxial and Organ boundary signalling, concluding that HWS may have a wider function in different signalling pathways than previously proposed.

The research was undertaken at a sand dune system located along the South East coast of England, known as Sandwich Bay. Sandwich Bay has attracted a number of environmental designations, including Special Areas of Conservation and a Site of Special Scientific Interest due to the presence of rare habitats and flora found predominantly at this single site, such as Himantoglossum hircinum (lizard orchid) and Orobanche caryophyllacea (bedstraw broomrape). The research focus centred on concerns surrounding ecological change resulting in the loss of grey dunes, an Annex 1 priority feature. Sandwich Bay has been classed as a Special Site of Scientific Interest in unfavourable condition (Natural England, 2014), based primarily upon the loss of fixed grey dune habitats to neutral grasslands (SD8 to MG1/MG12 NVC classifications). The aim was to identify causative factors that might account for the observed historic and any current changes in vegetation. The research was conducted between October 2011 and September 2014, and focused upon hydro-chemical interactions in the environment. Analysis was undertaken by the installation of 103 dipwells across the 520 ha site, in order to obtain groundwater samples. The hydro-chemical and botanical analysis indicated that the vegetation composition was not affected significantly by the chemical constituents within the groundwater. However vegetation composition was significantly modified by variable surface elevation and the related height of the water table. An additional investigation focused upon the identification of management techniques that are thought to be beneficial to dune vegetation restoration. Three management trials were located at three different sites, investigating four different management treatments. Analysis showed that there was a significant difference between the various management treatments and species composition. Vegetation analysis indicated that both cut and remove, and burning, as management treatments encouraged a greater diversity of species, particularly in sheltered eutrophic areas.

No description available.

No description available.

Suaeda maritima is an annual halophyte commonly found in salt-marshes. Its salt tolerance has been well studied, though there is little published on the effect of simultaneous waterlogging. The effects of saline waterlogging on growth, antioxidants (glutathione and total polyphenolic compounds, antioxidant activity) and oxidative damage were investigated with simulated tides in a controlled glasshouse and on plants collected from the field. Flooded shoots possessed higher levels of antioxidants than those from plants growing in well-drained situations, in the glasshouse and the field. The effects of hypoxia, (simulated in nutrient solution by flushing with nitrogen in a solution containing a low concentration of agar, which limits convection within the solution and so the transport of oxygen from the air) were determined on growth and trace metal concentrations, in plants grown in different concentrations of artificial seawater (100 and 350 mM Na+ at low pH, > pH 5.5), in sand/mud irrigated with halfstrength fresh seawater (at high pH, ca 7-8) and in different concentrations of manganese and iron in solution culture. High salt concentration reduced accumulation of trace metals in plants. Optimal growth occurred in 14 μM Fe and 1 mM Mn. Accumulation of trace metals was reduced at high pH, with more accumulating in the roots than the shoots. Hypoxia increased soluble sugars in shoots and roots, and this was affected by the salt concentration. Hypoxia also caused adventitious root development in hydroponic experiments, while in sand, adventitious root development was greater in drained than flooded conditions. Hypoxia significantly reduced shoot sodium concentration, sodium flux and bypass flow, at low and high salt concentrations. In high salt conditions, S. maritima reduced its transpiration rate and improved its water use efficiency. It was also shown that the roots contained high lactate concentrations under aerated and hypoxic conditions. S. maritima demonstrated many adaptations for tolerating extreme hypoxia.

Flooding events are becoming more common throughout the world as a result of climate change, resulting in reduced crop yields. It was recently discovered that plants sense low oxygen (O2) (associated with flooding) through regulated proteolysis of the group VII Ethylene Response Factor transcription factors (ERFVIIs), via the Cys-Arg/N-end rule pathway of ubiquitin mediated proteolysis, which also senses another gas, nitric oxide (NO). The N-terminal (Nt) Cys of physiological (e.g. ERFVIIs) and artificial substrates was shown to be key for N-end rule function, and work in mammalian systems suggested that oxidation of Nt-Cys by O2 and NO was a required prerequisite for subsequent Nt arginylation by arginyl tRNA transferases (ATEs). However the exact mechanism of Nt-Cys oxidation has not been discovered. The primary aim of this thesis was to define the mechanism of in vivo Nt-Cys oxidation essential in determining the stability of Arg/N-end rule protein substrates, including ERFVIIs. In this study a novel approach was developed to investigate the oxidation of Nt-Cys in vivo using transgenic Arabidopsis expressing Cys-2 reporter proteins (derived from the transgenes 35S::MC-polyG-HA-GUS and Ubi1::MCGGAIL-GUS). Cys-2 of the reporter proteins is made Nt constitutively by co-translational Methionine Aminopeptidase (MAP) activity. Biochemical techniques were combined with analytical chemistry to investigate the in vivo oxidation of Nt-Cys using liquid chromatography mass spectrometry (LC-MS). In addition, synthetic peptides representing the Nt-sequence of the in vivoreporter protein were used to define the oxidative and nitrosylative modifications occurring at Nt-Cys in vitro. Findings of this study include the successful development of two new in vivo O2 sensor artificial N-end rule substrates, in the plant genetic model Arabidopsis thaliana. A further outcome revealed that the ERFVII RELATED TO APETALA 2.12 (RAP2.12) is stabilised in the shoot and root apical meristem to a greater extent than in other regions of seedlings in response to hypoxia, indicating that meristematic cells could be important oxygen sensory zones. Cys-2 reporter proteins were used in in vivo studies to attempt to identify the nature of the Nt residues following N-end rule action. Although Nt-peptides derived from affinity purified Cys-2 reporter protein were not identified by LC-MS, it was possible to demonstrate that ubiquitination is required on Cys-2 reporter proteins before 26S proteasome degradation. Combined results from Nt-Cys in vitro synthetic peptides and Cys-2 reporter proteins substrates of the Arg/N-end rule pathway, provide indirect evidence that post translational modifications (PTMs)not defined before occur in vivo. Using synthetic peptides it was possible to show evidence for Nt-Cys-sulfenamide formation after oxidation of Nt-Cys. This finding suggests that Cys-sulfenamide formation, a previously recognised reversible modification preventing irreversible oxidation to Cys-sulfonic acid, could occur at Nt-Cys of in vivoprotein substrates. An important finding of this study was the observednonreactionbetween the nitrosylated Nt-Cys and H2O or conversely oxidised Nt-Cys and NO. As Plant Cysteine Oxidases (PCOs) do not require NO to oxidise Nt-Cys, this result raises further uncertainty as to how NO is involved in the oxidation of Nt-Cys, suggesting that NO may be involved in the enzymatic activation of PCOs or the arginylation of Nt-Cys by ATEs. The findings of this study did not identify the Nt-peptide of the Cys-2 reporter protein, and hence the Nt-Cys oxidation state of an in vivo substrate of the Arg/N-end rule pathway remains unidentified. Despite this the result that Nt-Cys can be oxidised to Cys-sulfenamide is novel and an important discovery to the field of reactive Cys biology and chemistry.

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Thesis (Ph. D.)--Oregon State University, 1962. / Typescript. Includes bibliographical references (leaves 129-134). Also available on the World Wide Web.