Photosystem I (PSI) is one of the chlorophyll-protein complexes located in the thylakoid membranes of photosynthetic organisms. It catalyses the oxidation of reduced plastocyanin or cytochrome C6 and reduction of ferredoxin or flavodoxin during photosynthesis. The complex is composed of two core subunits, PsaA and PsaB, which bind electron-carrying cofactors, and numerous low molecular weight subunits. The precise composition of small subunits varies between prokaryotic and eukaryotic PSI and the function of many of these subunits remains unclear. This thesis describes studies of cyanobacterial mutants lacking small subunits in order to clarify the function of the PsaL and PsaE subunits. The subunit PsaE has been implicated in the interaction of PSI with ferredoxin and in cyclic electron transport. In cyanobacteria a trimeric form of PSI predominates, with PsaL acting as the point of contact between three monomer units. Cyanobacterial mutants lacking this subunit therefore produce only monomeric PSI. No evidence of trimerisation has been found for PSI in eukaryotic organisms. This study has established growth conditions in which PsaL-lacking mutants are disadvantaged compared to wild type. An investigation into the interaction of monomeric PSI with light-harvesting structures such as the phycobilisomes and the iron stress-induced CP43' antenna ring revealed that trimerisation of PSI is not required for interaction with either structure. However, the rates of state transitions and phycobilisome diffusion were measured and compared to those of wild type cells, revealing an increase in rate in both cells when PSI is monomeric. This suggests a change in the stability of the phycobilisome-PSI interaction. EPR analysis of electron transfer processes in cyanobacterial mutants lacking the PsaE subunit and of PSI in either monomeric (PsaL-lacking) or trimeric (wild type) forms has been conducted. Possible functional roles for PSI trimerisation are discussed.

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This thesis reports a study on the variation of two genera of blue-green algae, Calothrix and Rivularia. The aspects chosen for detailed study were tapering and the hair. Before any comparative work could be undertaken it was necessary to develop ways of describing, in a quantitative manner, changes in the tapering and hair length. Tapering proved to be complex to describe in a satisfactory manner but four simple indices have been suggested. Measurements of individual trichomes have shown problems inherent in detailed studies of tapering, and the indices suggested by the author have been discussed in relation to this. Experimental studies on tapering have been concerned with elaborating the observations of previous authors that, in the presence of combined nitrogen, Calothrix and Gloeotrichia did not develop their characteristic taper. The effect of combined nitrogen on morphology was studied using the tapering indices. Attempts to culture material with hairs proved difficult; however a few factors which affect the development of the hair have been described. A computer program was developed in order to summarise relationships between the occurrence of hairs and other morphological features which have been described in the literature. For practical reasons it was often necessary to assign a name to members of the genus Rivularia; however in doing this many problems were encountered. To overcome some of these difficulties an objective method of identification was devised. This was used in particular to identify material collected in the field. A brief ecological survey of Rivularia was undertaken in order to study possible correlations between certain aspects of water chemistry and the occurrence of members of the genus.

Cyanobacterial secondary metabolites can cause serious harm to animals and humans (cyanotoxins) and can have a major financial impact on the potable water and aquaculture industries (taste and odour compounds). Understanding the factors that affect cyanotoxin production can help in exploring means for the control of these secondary metabolites. One of the most prominent cyanotoxins are microcystins and their sister compound nodularin. The biological role of microcystins is poorly understood. A pheromonal effect was observed applying a novel stable isotope labelling (15N) method. Microcystin- LR has been shown to stimulate culture growth, limit microcystin synthesis, and affect the distribution of microcystin-LR between the intra- and extracellular matrices. Furthermore the control of microcystins in potable water has been explored applying photocatalysis over titanium dioxide. A novel product called Photospheres™ was assessed in its photocatalytic efficiency in the destruction of 12 microcystin analogues and nodularin. The photocatalytic efficiency of the Photospheres™ was further explored in the degradation of four common waste water pollutants (2-chlorophenol, p-cresol, Acid Orange 74, and trichloroethylene) and in a custom built reactor using light emitting diodes as source of irradiation. The monitoring and regulation of cyanobacterial taste and odour compounds, especially geosmin and 2- methylisoborneol is important in the potable water and aquaculture industries. A rapid, robust, sensitive, and cost-effective analysis method using SPE-GCMS has been developed and is capable of detecting both compounds to sub nano gram levels. The method was successfully applied on spiked laboratory and environmental samples (loch and fishfarm waters). The photocatalytic destruction of both 2-methylisoborneol and geosmin was explored with a custom built flow reactor that was able to degrade > 95 % of both compounds in spiked and environmental samples. Furthermore the application of silicone rubber membranes as passive samplers was explored in spiked and environmental samples, demonstrating that silicone rubber membranes can successfully be used in environmental applications to deliver rapid and accurate determinations of both 2-methylisoborneol and geosmin.