Alternative electron transport pathways in photosynthesis: a confluence of regulation

Abstract

Photosynthetic reactions proceed along a linear electron transfer chain linking water oxidation at photosystem II (PSII) to CO reduction in the Calvin-Benson-Bassham cycle. Alternative pathways poise the electron carriers along the chain in response to changing light, temperature and CO inputs, under prolonged hydration stress and during development. We describe recent literature that reports the physiological functions of new molecular players. Such highlights include the flavodiiron proteins and their important role in the green lineage. The parsing of the proton-motive force between ΔpH and Δψ, regulated in many different ways (cyclic electron flow, ATPsynthase conductivity, ion/H transporters), is comprehensively reported. This review focuses on an integrated description of alternative electron transfer pathways and how they contribute to photosynthetic productivity in the context of plant fitness to the environment.

Diurnal and seasonal variations in the photosynthetic performance and chlorophyll fluorescence of cassava 'Rayong 9' under irrigated and rainfed conditions

“…Similar increase in the ratio of electron transport to CO2 assimilation under stresses was also observed in Jatropha curcas under drought stress (Sapeta et al 2013) and maize under cold stress (Fryer et al 1998). The proposed alternative electron sinks under stressful conditions included nitrogen metabolism, O2 reduction via photorespiration, the Mehler reaction, transport of reductants to mitochondria via malate, and cyclic electron flow via PGR5/PGPR1 proteins (Alric and Johnson 2017). The diversion of reductants from CO2 assimilation to alternative electron sinks during stresses, which impose restriction to photosynthetic carbon assimilation, could be a mechanism for preventing photodamage to the photosynthetic apparatus that operates in conjunction with NPQ (Peltier et al 2010).…”

The regulation of P700 is an important photoprotective mechanism to NaCl‐salinity in Jatropha curcas

“…This excess energy within the thylakoids increases the production of ROS, primarily superoxide radical and singlet oxygen. Coping with that, plants evolved to suppress excess energy generated in chloroplasts, primarily by photoprotective mechanisms as NPQ, photorespiration, water–water cycle and CEF (Alric and Johnson ). Photoprotection mechanisms at PSII level are well documented (Murchie and Niyogi , Derks et al ).…”

Identification and characterization of a core set of ROS wave‐associated transcripts involved in the systemic acquired acclimation response of Arabidopsis to excess light

“…Under such conditions the photosynthetic antennas absorb photons at a rate that is higher than the capacity of the photosynthetic centers to channel electrons through the electron transport chain (ETC) mechanisms, resulting in the production of singlet oxygen and other excited molecules. Electrons flowing through the ETC may additionally be transferred to alternative acceptors such as oxygen, resulting in the formation of superoxide radicals (Asada, ; Dietz, ; Alric and Johnson, ). Because CO 2 fixation is dependent on stomatal conductance and temperature, excess light may pose an even bigger challenge to plants when it is combined with other stresses, such as drought or temperature stress, that limit the rates of CO 2 fixation (Mittler, ).…”