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Erik H. Murchie, Krishna K. Niyogi, Manipulation of Photoprotection to Improve Plant Photosynthesis, Plant Physiology, Volume 155, Issue 1, January 2011, Pages 86–92, https://doi.org/10.1104/pp.110.168831
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Light is of course essential for photosynthesis and supports most life on earth. However, light intensity and spectral quality are highly variable in space and time according to time of day, season, geography, climate, and the position of leaf within canopy and cell within leaf. This has resulted in the evolution of a remarkable suite of processes within the photosynthetic system to accommodate these fluctuations. In fact, these regulatory mechanisms are tightly integrated with photosynthesis itself, and there is emerging evidence that when these processes are altered, the ability of plants to assimilate carbon over long time periods and to produce biomass may be affected.
Photosynthesis begins with the absorption of light by chlorophyll, much of which is located in the light-harvesting complexes (LHCs) of PSII and PSI within the thylakoid membrane of chloroplasts. Chlorophyll enters its singlet excited state, and excitation energy is transferred to PSII and PSI reaction centers where charge separation occurs and photosynthetic electron transport is initiated. Electrons derived from water splitting ultimately reduce NADP+ to NADPH, and the transmembrane ƊpH is used to drive ATP generation by the chloroplastic ATP synthase. NADPH and ATP are then used in the Calvin-Benson cycle and other assimilatory reactions. In addition to this linear electron flow, there is flexibility in the electron transport system with multiple pathways and electron acceptors possible. These include cyclic electron transfer and oxygen as an electron acceptor.
