3. Results
To distinguish dark and light-mediated metabolic changes in guard cells, we performed a 13C-HCO3 labelling experiment. Guard cells were harvested pre-dawn and subjected to 0, 10, 20 and 60 minutes of continuous darkness or following transfer to white light conditions (400 µmol photons m-2s-1). Primary metabolites were identified and used to compare the changes at both metabolite content and13C-enrichment. Whilst changes in the content of metabolites indicate alterations in the pool of them throughout the experiment, the 13C-enrichment analysis demonstrates the 13C distribution derived from CO2assimilation mediated by PEPc in the dark and by both PEPc and RuBisCO in the light.