Thesis subject

Light Harvesting and Photoprotection in Cyanobacteria

PhD Thesis Tian Lijin, 8 May, 2013

The purpose of this thesis is to obtain an in-depth understanding of the early steps of photosynthesis of cyanobacteria at the molecular level in vivo by using picosecond time-resolved fluorescence techniques. These steps include sunlight energy-harvesting process, energy trapping and nonphotochemical quenching (NPQ). More precisely, one NPQ process, called blue-green light-induced NPQ, has been studied intensively, thereby becoming the focus of this thesis.

the first crucial processes after the absorption of a photon. Many picosecond studies have also been performed in vivo in the past before the crystal structures were known, but due to an additional lack of knowledge about the organization and composition of the thylakoid membrane where most of the EET and CS processes take place, the obtained results were difficult to interpret. More recently, new interest has arisen in in vivo studies on photosynthetic organisms because a lot of molecular and organizational information has been obtained but also because the spectroscopic techniques have improved and mutants have become available that allow to study the effect of specific modifications in the organisms. This thesis focuses on the study of the light energy harvesting processes of photosynthetic complexes in cyanobacteria in general by using timeresolved fluorescence techniques, and with particular emphasis on the study of the protective process of non-photochemical quenching (NPQ) that is induced in the presence of high intensities of blue-green light. One of the important goals of researchers in the field of photosynthesis is to determine the photosynthetic efficiencies, to understand the underlying molecular mechanisms and to ultimately improve these efficiencies under certain conditions. In order to do so, one is forced to go down to the molecular level and to the picosecond time scale as is also pointed out in the introduction of this thesis. In the studies described in this thesis we have successfully combined spectrally-resolved, picosecond fluorescence measurements on wild-type and mutant cells of Synechocystis PCC 6803 with global and target data analysis, and a summary of the main findings is presented below.