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Potato tuber flesh colour is a quality trait dependent on the types and levels of carotenoids. These, together with many plant growth regulators, sterols and terpenes, are isoprenoid derived compounds. Even though carotenoids have been extensively studied due to their importance in photosynthesis and nutrition, a clear understanding concerning the regulation of their accumulation and localisation in plant storage organs is lacking. The present study describes two strategies to investigate the regulation of carotenoid biosynthesis in potato. Firstly, in order to localise the site of synthesis of tuber carotenoids, stable transgenic potato plants were generated. These expressed two key carotenoid biosynthetic genes, PHYTOENE SYNTHASE 2 (PSY2) and B-CAROTENE HYDROXYLASE 2 (CrtRb2), fused to red fluorescent protein (RFP). The expression and carotenoid levels were significantly increased, confirming functionality of the protein-RFP ensembles. Confocal microscopy on developing tuber tissue made it possible to obtain images ofPSY2•RFP and CrtRb2- RFP localisation into amyloplasts. Secondly, the effect of carotenoid degradation was addressed as a potential regulator of accumulation, based on the recent discovery that a CAROTENOID CLEAVAGE DIOXYGENASE 4 (CCD4) reduces carotenoid levels in potato tubers. CeD8 is another important member of the ('CD gene family, with a role in strigolactone biosynthesis. In this study, C'CD8-RNAi knock out lines were characterised. Although CeD8 down-regulation did not significantly affect carotenoid content, a range of interesting above and below ground phenotypes was observed. Importantly, the study showed that the CCD8 gene product impacts on stolon branching, tuber development and tuber dormancy.

Photosynthesis is a naturally occurring process that converts sunlight into stored chemical energy. The artificial recreation of this process is highly desirable as a way of obtaining renewable energy sources and has attracted considerable research effort over many decades. A common feature of both natural and artificial photosynthesis involves the transfer of lectronic energy between molecules, with the photon ultimately being trapped at a specific site. This research project looks at a series of boron dipyrromethene (Bodipy) dyes coupled with various chromophores and examines their ability to duplicate the energy-transfer steps found in the natural organism. We focus mostly on electronic energy transfer between the closely-spaced chromophores using experimental approaches, in particular steady-state and time-resolved fluorescence spectroscopy.

Investigations in this thesis aimed to understand the mechanisms that regulate the photosynthetic electron transport chain in C3 plants and therefore also the significance of cyclic electron flow (CEF). Physiological analysis of Arabidopsis thaliana photosynthetic pgr5 mutant, which had previously been reported to be a CEF mutant, were undertaken. The reduced state of P700 in the light meant that standard assays for P700 and CEF, using P700 absorbance could not be applied. Design and development of flash spectrophotometric techniques were necessary. This primarily involved P700 oxidation kinetics at 820 nm combined with the electrochromic shift at 520 nm to measure electrical field generation.

Understanding how plant productivity responds to CO2 is crucial to understanding Earth System dynamics and therefore, predicting the Earth System's response to anthropogenic forcing of atmospheric CO2. Free Air Carbon dioxide Enrichment (FACE) experiments test the CO2 response of semi-natural forest stands over the course of a decade of CO2 enrichment and this Thesis informs and develops global carbon cycle modelling using FACE data. Meta-analysis of FACE experiments showed maintained productivity gains, and no evidence of photosynthetic acclimate to elevated CO2, over nine years of enrichment. An artefact of FACE methods is that CO2 concentrations oscillate at high frequency (1 oscillation per minute) and high amplitude (400–900 µmol mol-1) with the potential to impact carbon assimilation. Chapter three demonstrated that carbon assimilation was increased in Quercus robur and Populus x euramericana compared to steady state CO2. Simulation of the Oak Ridge and Duke FACE experiments showed that both the Sheffield Dynamic Global Vegetation Model (SDGVM) and the Joint UK Land Environment Simulator (JULES) could reproduce Net Primary Productivity (NPP) with a reasonable degree of accuracy once Vcmax was accurately parameterised. This research highlights the necessity of rigorous model testing with observed data and shows the need to develop a strong, cross model, benchmarking system. A global meta-analysis assessed the response of Vcmax to leaf nitrogen and phosphorus showing that phosphorus reduced the sensitivity of Vcmax to nitrogen. Global simulation with the empirical Vcmax to leaf nitrogen and phosphorus relationship led SDGVM to over-predict Gross Primary Productivity (GPP) and biomass, yet lowered terrestrial CO2 sequestration over the course of the 20th and 21st century due to higher rates of soil respiration. Model bias and compensating factors are highlighted and correction of parameterisation error showed that more explicit process representation is necessary in SDGVM. Areas highlighted for model development were: nitrogen cycle simulation; Vcmax and Jmax; parameterisation; experimental quantification of the effect of soil water stress on forest productivity and the simulation of biomass and mortality. Accurate global datasets of biomass, NPP and leaf traits will help to uncover model bias and compensating factors and will help to develop model processes.

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