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PEPc-mediated CO2 assimilation provides carbons to gluconeogenesis and the TCA cycle in both dark-exposed and illuminated guard cells
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  • Valéria Lima,
  • David Medeiros,
  • Silvio Cândido‐Sobrinho,
  • Francisco Freire,
  • Nicole Porto,
  • Alexander Erban,
  • Joachim Kopka,
  • Markus Schwarzländer,
  • Alisdair R. Fernie,
  • Danilo Daloso
Valéria Lima
Universidade Federal do Ceara
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David Medeiros
Max Planck Institute of Molecular Plant Physiology
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Silvio Cândido‐Sobrinho
Universidade Federal do Ceara
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Francisco Freire
Universidade Federal do Ceara
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Nicole Porto
Universidade Federal do Ceara
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Alexander Erban
Max-Planck Institute of Molecular Plant Physiology
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Joachim Kopka
Max-Planck Institute of Molecular Plant Physiology
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Markus Schwarzländer
Universität Bonn
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Alisdair R. Fernie
Max-Planck Institute for Molecular Plant Physiology
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Danilo Daloso
Universidade Federal do Ceara

Corresponding Author:daloso@ufc.br

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Abstract

Evidence suggests that guard cells have higher rate of phosphoenolpyruvate carboxylase (PEPc)-mediated dark CO2 assimilation than mesophyll cells. However, it is unknown which metabolic pathways are activated following dark CO2 assimilation in guard cells. Furthermore, it remains unclear how the metabolic fluxes throughout the tricarboxylic acid (TCA) cycle and associated pathways are regulated in illuminated guard cells. Here we used 13C-HCO3 labelling of tobacco guard cells harvested under continuous dark or during the dark-to-light transition to elucidate principles of metabolic dynamics downstream of CO2 assimilation. Most metabolic changes were similar between dark-exposed and illuminated guard cells. However, illumination increased the 13C-enrichment in sugars and metabolites associated to the TCA cycle. Sucrose was labelled in the dark, but light exposure increased the 13C-labelling into this metabolite. Fumarate was strongly labelled under both dark and light conditions, while illumination increased the 13C-enrichment in pyruvate, succinate and glutamate. Only one 13C was incorporated into malate and citrate in either dark or light conditions. Our results collectively suggest that the PEPc-mediated CO2 assimilation provides carbons for gluconeogenesis, the TCA cycle and glutamate synthesis and that previously stored malate and citrate are used to underpin the specific metabolic requirements of illuminated guard cells.