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Phosphorus (P) and Zinc (Zo) are essential nutrients for plant growth. Plants typically have a [P] leaf of 3 mg P g-1 dry weight. Most plants contain leaf Zn concentrations [Zn]leaf of <0.1 mg Zn g- 1 dry weight (DW)- [P]leaf and [Zn]leaf vary substantially according to the characteristics of the growing media and due to genetic factors. A complex relationship between [P]leaf and [Zn]leaf, known as P-induced Zn deficiency (PIZnD), has been documented in several crop species, in which high levels of [p]ext appear to induce Zn deficiency symptoms, although the mechanism by which this occurs is not known. The aim of this project was to gain a greater understanding of the relationship between [P]leaf and [Zn]leaf in planta, using Arabidopsis thaliana (L.) Heynh as a model system. The first scientific objective was to explore the relationship between [P]leaf and [Zn]leaf at a physiological level, in which the growth and global mineral composition of leaves were determined over at a range of external concentrations of P ([P]ext). The second scientific objective was to determine the effect of [P]ext on global changes in gene expression. The overarching hypothesis was that increases in [P]ext lead to increases in [P]leaf which, in turn lead to down regulation of genes which are involved in Zn uptake and transport. Two sets of technical experiments were conducted to optimise an assay system used to induce P toxicity symptoms. First, to optimise leaf mineral analysis, plant certified reference materials were used to determine the minimum weight of material required for analysis using inductively coupled plasma atomic emission spectrometry (ICP-AES), and this was compared to established inductively coupled plasma mass spectrometry (ICP-MS) techniques. This experiment demonstrated that 0.3 g DW of a cabbage standard reference material was sufficient to accurately and precisely detect the composition of nine elements, including P and Zn. Second, plants were grown in an in vitro cultivation system comprising a minimal agar, supplemented with mineral salts at eight [P]"" levels (0 to 10 mM)- Shoot and root fresh and dry weights and mineral composition were measured after 14 d of growth.

The first section of this thesis describes the synthesis of procyanidin B3, a dimeric flavanoid consists of monomeric (+}-catechin and a member of the polyphenol family. A study of the leaving groups at C4 catechin together with Lewis acid activator effects on the formation of the interflavan hond formation was conducted. A range of electrophilic ethers was prepared via DDQ oxidation and a1coholic trapping (propanol, crotyl a1rohol and propargyl alcohol) at the C4 position of (+}-catechin. The Lewis acid-mediated nucleophilic C4 substitution of each of these ethers was examined and it was found that the propargyl ether was the best overall e1ectrophile. A range of Lewis acids were then examined as activators and it was found that BF3oOEt2 was the best in terms of both yield and stereochemical control at the C4 position. In our view, the strength of the nucleophiles used contributed mainly to the diastereoselectivity preference for the substitution reactions. This newly developed set of conditions was then used to prepare the natural product nutraceutical procyanidin B3 with high control of diastereoselectivity. To extend the versatility of this synthesis, a novel dimeric polyphenol analogue was synthesised utilising the optimum conditions used for the synthesis of pro cyanidin B3. The second section of this thesis is devoted to the synthesis of novel morpholino antisense oligonucleotides. Herein, the synthesis of amine and amide triazolelinked Morpholinos (TI.Morpholinos) using click copper-catalysed Huisgen [3 + 2] cycloaddition is illustrated. Replacing the charged phosphodiester backbone with a neutral, achiral 1.2.3-triazole linkage was chosen to improve the biostability in antisense applications. The synthesis of terminal alkyne morpholinos and examples of azide monomers required for the click chemistry was successfully achieved. The synthesis presented in this work tolerated a range of functionalities and was amenable to all nucleosides. The amine and amide TI.Morpholino oligonucleotides were constructed using the standard solid-phase DNA synthesis. Both the amine and amide TLMorpholinos formed were characterised by MALDITOF and HPLC experiments. The thermal stability of the amine and amide TI.Morpholinos relative to a standard DNA was assessed and it was found that the amine and amide triazole linkages stabilised the DNA duplex. It was concluded that these modifications enhanced the stability of the DNA duplex and consequently might contribute to the development of new candidates for the antisense applications

Ferredoxin NADP+ oxidoreductase (FNR) enzymes catalyse electron transfer between ferredoxin and NAD(P)H. A photosynthetic FNR (pFNR) in plants catalyses the final step of linear electron flow (LEF) in photosynthesis by transferring electrons from reduced ferredoxin to NADPH, providing reductant for carbon fixation. Various alternative electron flow pathways require reductant in the form of ferredoxin. pFNR may, therefore, be crucial to the regulation of reductant partition between carbon fixation and other metabolic pathways.

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