PhD thesis Reza Ranjbar Choubeh, 19 November, 2018
Photosynthetic organisms live under variable conditions, which demands short-term adaptation to avoid damage to photosynthetic antennas. The main topic of this thesis is the study of the variation of light harvesting in different physiological conditions in cyanobacteria Synechococcus elongatus 7942 and Leptolyngbya ohadii.
Photosynthetic organisms live under variable conditions, which demands short-term adaptation to avoid damage to photosynthetic antennas. The main topic of this thesis is the study of the variation of light harvesting in different physiological conditions in cyanobacteria Synechococcus elongatus 7942 and Leptolyngbya ohadii.In this introduction, early steps of photosynthesis and some of the photosynthetic complexes are explained and then an introduction of fluorescence and its acquisition is presented. Data analysis that is necessary to make sense of the recorded timeresolved fluorescence follows next. At the end, the organization of this thesis is given.
Photosynthesis, cyanobacteria, and state transitions
Photosynthetic organisms convert light energy into chemical energy to sustain their
metabolism, but which can also be used by other living organisms. Photosynthetic
reactions are divided into light-dependent and light-independent reactions
(Blankenship 2008a). Plants and cyanobacteria produce Adenosine Triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) during the light-dependent reactions. In the light-independent reactions, ATP and NADPH are used to fix carbon dioxide into carbohydrates.
The light-dependent reactions start with the absorption of light by the photosynthetic antennas. Cyanobacteria use phycobilisomes (PBSs) and photosystems I and II (PSI and PSII) to absorb light (Figure 1). PBSs are the main light-harvesting antennas in cyanobacteria which mainly absorb green-orange light. They are composed of rodlike proteins and core proteins. (MacColl 2004; Mirkovic et al. 2016). The rods are built of C-phycocyanins (CPCs) and in various organisms they also have phycoerythrins (PEs). The rods are attached to allophycocyanins (APCs), which contain APC trimers and three other protein-pigments, namely LCM, β16, and αB. The excitation energy absorbed by PEs and PCs travels along the rods and reaches APCs, which are attached to the rods by linker proteins, and from there it is delivered to LCM and αB. LCM and αB transfer the excitation energy to chlorophyll (Chl) a of PSI and PSII.