Abstract
Water oxidation in photosynthesis takes place in photosystem II (PSII). This photosystem is built around a reaction center (RC) where sunlight-induced charge separation occurs. This RC consists of various polypeptides that bind only a few chromophores or pigments, next to several other cofactors. It can handle far more photons than the ones absorbed by its own pigments and therefore, additional excitations are provided by the surrounding light-harvesting complexes or antennae. The RC is located in the PSII core that also contains the inner light-harvesting complexes CP43 and CP47, harboring 13 and 16 chlorophyll pigments, respectively. The core is surrounded by outer light-harvesting complexes (Lhcs), together forming the so-called supercomplexes, at least in plants. These PSII supercomplexes are complemented by some “extra” Lhcs, but their exact location in the thylakoid membrane is unknown. The whole system consists of many subunits and appears to be modular, i.e., both its composition and organization depend on environmental conditions, especially on the quality and intensity of the light. In this review, we will provide a short overview of the relation between the structure and organization of pigment-protein complexes in PSII, ranging from individual complexes to entire membranes and experimental and theoretical results on excitation energy transfer and charge separation. It will become clear that time-resolved fluorescence data can provide invaluable information about the organization and functioning of thylakoid membranes. At the end, an overview will be given of unanswered questions that should be addressed in the near future.
Highlights
The photosynthetic light reactions of green plants, algae, and cyanobacteria take place in photosystems I and II (PSI and photosystem II (PSII))
The reaction center (RC) is located in the PSII core that contains the inner light-harvesting complexes CP43 and CP47, harboring 13 and 16 chlorophyll pigments, respectively
We will provide a short overview of the relation between the structure and organization of pigment-protein complexes in PSII, ranging from individual complexes to entire membranes and experimental and theoretical results on excitation energy transfer and charge separation
Summary
The photosynthetic light reactions of green plants, algae, and cyanobacteria take place in photosystems I and II (PSI and PSII). Light-induced charge separation in the reaction center (RC) of PSII leads to the oxidation of water, the reduction of plastoquinone and the formation of a proton gradient across the thylakoid membrane in which PSI and PSII are embedded, which is crucial for the production of ATP. Photosynth Res (2013) 116:251–263 molecules (see (Umena et al 2011) for the most recent PSII core structure) Both antenna complexes feed excitation energy into the RC. Plants and green algae possess membrane-embedded antennae with a high pigment/protein ratio (*1:2 regarding the mass), called outer light-harvesting complexes (Lhcs) and to a large extent they are organized in larger supercomplexes, together with the PSII cores. We will focus on the study of EET and CS in PSII, starting with the core, followed by outer antenna complexes and supercomplexes. We would like to refer to other reviews from recent years for further information (Renger and Schlodder 2010; Vassiliev and Bruce 2008; Renger 2010; Van Amerongen et al 2003; Minagawa and Takahashi 2004; Barber 2002; Muh et al 2008; Renger and Renger 2008; Croce and van Amerongen 2011)
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