Extract

Oxygen (O2) is evolved during photosynthetic electron transport when water is split by the oxygen-evolving complex to provide protons and electrons to the chloroplastic electron chain, thereby generating ATP and NADPH—the energy source and reducing power for plant metabolism. The majority of this chemical energy is used to drive photosynthetic carbon metabolism, which consists of ribulose-1,5-bisphosphate carboxylation (photosynthetic carbon reduction cycle) and oxygenation (photosynthetic carbon oxidation cycle); with a combined electron requirement = JA. Four electrons are required for every O2 evolved so that gross O2 production (GOP) is related to linear electron transport (J) according to J/4. When linear electron transport is used only to drive CO2 fixation, the consumption of O2 and the release of CO2 by photosynthetic carbon oxidation and mitochondrial respiration is such that net O2 production (NOP) is equal to net CO2 assimilation (Anet; provided the respiratory quotient is 1, but see Tcherkez et al., 2017).

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