LHCII-assisted TiO2 photocatalysis of CO2 to small organic compounds

CO2 photoreduction could be used to convert CO2 from the emissions of fossil-fuel power plants back into fuel using solar energy and photocatalysts such as TiO2. However, TiO2 absorbs UV light which is only a small portion of the solar radiation. Plants use the Light Harvesting Complex of photosystem II (LHCII) to maximise light absorption in photosynthesis. The work presented in this thesis investigates the combination of the LHCII and Rh-doped TiO2 photocatalyst, to increase the visible light absorption of the catalyst and improve its efficiency. LHCII was extracted from spinach leaves and adsorbed on to the TiO2:Rh catalyst surface. The presence of LHCII on the surface was confirmed by LHCII-specific peaks in absorption and fluorescence spectra. The performance of TiO2:Rh-LHCII was assessed in CO2 photoreduction with simultaneous water splitting. Methane, CO, methyl formate, acetaldehyde and hydrogen were detected in the reactor and the concentrations of all but CO, were greatly increased for TiO2:Rh-LHCII compared to TiO2:Rh in visible light experiments. Ordinary differential equation (ODE) models were developed for CO2 photoreduction to investigate the steady-state concentrations of the products and make predictions about their response to different experimental parameters. The light absorption was confirmed as a viable optimisation target for increasing product concentrations. A stochastic discrete spatial model was also developed which showed that spatial effects are important for reduction rates and that the hydrophilicity of the catalyst may lead to reaction stalling. It was concluded that, if issues with LHCII stability and maximising light absorption without interfering with catalysis are dealt with, LHCII could be a promising method for enhancing CO2 photoreduction with the appropriate catalyst

Single amino acid change alters specificity of the multi-allelic wheat stem rust resistance locus SR9

Most rust resistance genes thus far isolated from wheat have a very limited number of functional alleles. Here, we report the isolation of most of the alleles at wheat stem rust resistance gene locus SR9. The seven previously reported resistance alleles (Sr9a, Sr9b, Sr9d, Sr9e, Sr9f, Sr9g, and Sr9h) are characterised using a synergistic strategy. Loss-of-function mutants and/or transgenic complementation are used to confirm Sr9b, two haplotypes of Sr9e (Sr9e_h1 and Sr9e_h2), Sr9g, and Sr9h. Each allele encodes a highly related nucleotide-binding site leucine-rich repeat (NB-LRR) type immune receptor, containing an unusual long LRR domain, that confers resistance to a unique spectrum of isolates of the wheat stem rust pathogen. The only SR9 protein effective against stem rust pathogen race TTKSK (Ug99), SR9H, differs from SR9B by a single amino acid. SR9B and SR9G resistance proteins are also distinguished by only a single amino acid. The SR9 allelic series found in the B subgenome are orthologs of wheat stem rust resistance gene Sr21 located in the A subgenome with around 85% identity in protein sequences. Together, our results show that functional diversification of allelic variants at the SR9 locus involves single and multiple amino acid changes that recognize isolates of wheat stem rust

LHCII-assisted TiO2 photocatalysis of CO2 to small organic compounds

CO2 photoreduction could be used to convert CO2 from the emissions of fossil-fuel power plants back into fuel using solar energy and photocatalysts such as TiO2. However, TiO2 absorbs UV light which is only a small portion of the solar radiation. Plants use the Light Harvesting Complex of photosystem II (LHCII) to maximise light absorption in photosynthesis. The work presented in this thesis investigates the combination of the LHCII and Rh-doped TiO2 photocatalyst, to increase the visible light absorption of the catalyst and improve its efficiency. LHCII was extracted from spinach leaves and adsorbed on to the TiO2:Rh catalyst surface. The presence of LHCII on the surface was confirmed by LHCII-specific peaks in absorption and fluorescence spectra. The performance of TiO2:Rh-LHCII was assessed in CO2 photoreduction with simultaneous water splitting. Methane, CO, methyl formate, acetaldehyde and hydrogen were detected in the reactor and the concentrations of all but CO, were greatly increased for TiO2:Rh-LHCII compared to TiO2:Rh in visible light experiments. Ordinary differential equation (ODE) models were developed for CO2 photoreduction to investigate the steady-state concentrations of the products and make predictions about their response to different experimental parameters. The light absorption was confirmed as a viable optimisation target for increasing product concentrations. A stochastic discrete spatial model was also developed which showed that spatial effects are important for reduction rates and that the hydrophilicity of the catalyst may lead to reaction stalling. It was concluded that, if issues with LHCII stability and maximising light absorption without interfering with catalysis are dealt with, LHCII could be a promising method for enhancing CO2 photoreduction with the appropriate catalyst