Abstract
Measuring the carbon flux through metabolic pathways in intact illuminated leaves remains challenging because of, e.g., isotopic dilution by endogenous metabolites, the impossibility to reach isotopic steady state, and the occurrence of multiple pools. In the case of photorespiratory intermediates, our knowledge of the partitioning between photorespiratory recycling, storage, and utilization by other pathways is thus rather limited. There has been some controversy as to whether photorespiratory glycine and serine may not be recycled, thus changing the apparent stoichiometric coefficient between photorespiratory O2 fixation and CO2 release. We describe here an isotopic method to trace the fates of glycine, serine and glycerate, taking advantage of positional 13C content with NMR and isotopic analyses by LC–MS. This technique is well-adapted to show that the proportion of glycerate, serine and glycine molecules escaping photorespiratory recycling is very small.
Highlights
Illuminated leaves assimilate CO2 via gross photosynthesis and release CO2 via photorespiration and day respiration
Our method takes advantage of observed absolute 13 C amounts by NMR to provide an estimate of build-up rates of photorespiratory intermediates in illuminated leaves, using simple assumptions for calculations
For a broad range of gaseous (CO2 /O2 ) conditions, we found that the build-up rate of photorespiratory intermediates is a real phenomenon, but it is numerically very small compared to Φ and vo
Summary
Illuminated leaves assimilate CO2 via gross photosynthesis (carboxylation) and release CO2 via photorespiration and day respiration. Assuming that two oxygenation events are required for each photorespiratory CO2 release, we have the general relationships [2]: Accepted: 19 February 2021 Φ=
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