Fig. 1.

The scheme of the photosynthetic apparatus components and their interactions. Chlorophyll (Chl) and carotenoids (Car) are synthesised in plastids by nuclear coded enzymes (Yuan et al. 2017; Sun et al. 2018) and used for photosynthetic pigment-protein complex assembly. Electron transport chain (ETC) consists of the two photosystems, PSII and PSI, cytochrome b₆f complex (b₆f) and mobile electron carriers: plastoquinone pool (PQH₂/PQ) in the thylakoid membrane, plastocyanin (PC) in the lumen and ferredoxin (Fd) in the stroma. Light harvesting antennae, LHCII and LHCI, help to harvest light for PSII and PSI, respectively. Linear electron transport through ETC from H₂O to NADPH provides H⁺ cross-membrane transport and produces the proton gradient. ATP synthase uses this gradient energy for ATP synthesis. Calvin cycle of carbon assimilation from CO₂ to sugars consumes NADPH and ATP, produced by ETC. Generated trioses may be stored transiently in the chloroplast as starch or are exported and transported to other organs as sucrose and other sugars (Raines 2003). A part of the mobile pool of LHCII can disconnect from PSII with the help of serine/threonine kinase STN7 and PsbS subunit and move to PSI or dissipate absorbed light energy to heat (red curly arrows). Violaxanthin de-epoxidase (VDE) converts violaxanthin to zeaxanthin which quenches light energy in LHCII and PSII minor antennae. The major light input targets for photosynthetic apparatus formation, function and regulation are marked with red lightning symbols. Pigment-protein complexes containing Chls and Cars capture light for photosynthesis. Photoreceptors percept light and regulate gene expression and cell metabolism. In particular, photoreceptors control stomata development and opening. The light-dependent step in the Chl biosynthesis pathway is also marked