The thylakoids contain the membrane-protein complexes called photosystem I (PSI), photosystem II (PSII), cytochrome b6/f, and F-ATPase, which are the major players in oxygenic photosynthesis (Dekker and Boekema 2005; Moore et al. 1998; Nelson and Ben-Shem 2004). Both PSI and PSII contain a reaction center which is surrounded by a large “antenna”, which consists of light-harvesting pigment–protein complexes. The

chlorophylls TH-302 (Chls) and other pigments in the antenna harvest light and transport a large part of the corresponding energy to the reaction center in which charge separation takes place. In most plants and some green algae, the thylakoid membrane is differentiated into grana stacks and stroma lamellae (Fig. 1) (Anderson 1999; Dekker and Boekema 2005; Mustárdy and Garab 2003). Other classes of photosynthetic organisms have their own unique membrane stacking which is considerably different from that Buparlisib mw of higher plants (Gunning and Schwartz 1999). The dominant antenna species of PSII in higher plants is light-harvesting

complex II (LHCII) which is not only important for ‘”"harvesting light”" (van Amerongen and van Grondelle 2001), but also plays a role in nonphotochemical quenching (Pascal et al. 2005; Ruban et al. 2007), while it is, in addition, essential for grana stacking (Lambrev et al. 2007). PSI contains a large part that sticks out of the membrane and does not fit into the inner stacks of the grana. This leads to a separation of the two photosystems (Fig. 1) (Dekker and Boekema 2005). This separation is thought to allow the regulation of ATP production, by balancing the linear and cyclic electron transport (Berry and Rumberg 1996; Joliot et al. 2004) and to avoid ‘spill-over’. Fig. 1 Schematic model of the thylakoid membrane. The margins are the strongly curved membranes, the end membranes are located at the bottom and the top of the grana stack and the stroma lamella is the

non-stacked region In higher plants about ~85% of PSII is located in the grana and about ~15% is present clonidine in the stroma lamellae (Fig. 1), while for PSI these numbers are approximately 35 and 65%, respectively (Albertsson and Andreasson 2004). These percentages are not fixed but can differ between plant species while they also depend on growth conditions. However, the relative proportion of stroma lamellae and grana is rather constant (Albertsson and Andreasson 2004). The opposite is true for the number of layers in a single granum. Plants such as Alocasia that are grown in low-light intensities can have more than 50 layers in one granum, which can extend across the whole chloroplast (Goodchild et al. 1972), whereas most other plants have only ~10 till 20 layers. The diameter of the disc layer in the grana is more or less constant across plant species (300–600 nm) (Dekker and Boekema 2005; Mustárdy and Garab 2003).