Response of the photosynthetic system to altered protein composition and changes in environmental conditions

The photosynthetic thylakoid membrane has a hierarchically ordered structure containing pigment-protein complexes that capture solar radiation and convert it into chemical energy. Its highly dynamic structure is capable to continuously respond to the altered environmental conditions, e.g., light quality and quantity, temperature changes and nutrient availability. Having detailed knowledge about the photosynthetic apparatus and its regulating factors is of paramount importance for the potential use of photosynthesis as alternative energy source or for removing toxic pollutants. The thesis provides new information about the role of various carotenoid molecules for the structure and energy transfer capacity of photosynthetic complexes in cyanobacteria. Our results demonstrate that besides the known structural importance of carotenoids they are also required for the oligomerisation of photosystems and for maintaining the structure of the light-harvesting antenna complexes, called phycobilisomes. Part of the thesis focuses on the Photosystem II (PSII) macro-organisation in the chloroplast thylakoid membrane of plants. The general importance of a small-molecular-weight protein, PsbW is demonstrated for the organisation of the PSII supercomplexes and the formation of the parallel rows of PSII and the accompanying psi-type circular dichroism signal. A new, circular dichroism (CD) spectroscopy-based fingerprinting method is described that can be used to study the PSII macrodomain organization. CD is a potentially powerful method to follow the dynamic changes of the pigment-protein complex organisation of chloroplast membranes in vivo. In this thesis the cadmium-induced toxic effects on photosynthetic processes are also investigated. The observed changes can be merged into a cascade mechanism model. Such detailed knowledge of toxic events is crucial for the effective use of cyanobacteria to remove the cadmium pollution from water.In conclusion, this thesis contributes to our knowledge about the structure and dynamics of the photosynthetic apparatus at various organisational levels