The functional organization of Plant Photosystems: biochemical and spectroscopic analysis of the role of antenna proteins in photoprotection and acclimation to environmental conditions

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Photosynthesis is the process by which plants absorb solar energy and convert it to chemical energy to produce biomass. During this process some key functions are carried out by Photosystems. Photosystems I and II are the multiproteic complexes responsible for light harvesting, charge separation, and electron transport from water to NADPH. These events leads to the formation of a transmembrane ΔpH that is used by ATP-ases enzymes to produce ATP. PSI and PSII represent extraordinary machines for solar energy use, combining high quantum efficiency and the presence of inducible mechanisms in order to avoid photoinhibition. The peculiar organization of Photosystems is determinant for their functions. Both photosystems are composed by two moieties: a core complex and an antenna system constituted by the conserved Lhc proteins. This thesis focused into investigation of the functional organization of photosystems I (PSI) and II (PSII) using biochemical and spectroscopic methods. The role of the different Lhc subunits and the role of the specific pigments bound to them have been investigated through evaluation of basic functional properties of PSI and PSII, as the efficiency of light harvesting, stabilility and/or dynamic of the supercomplexes, mode of adaptation to different environmental conditions and activation of photoprotective mechanisms. We conclude that PSI and PSII strongly differs with respect to many fundamental properties of their mode of long term acclimation and short term protection to harmful conditions. However, at least one mechanism, namely chlorophyll triplet quenching, appears to be regulated in the same way in both.