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Tobacco guard cells fix CO 2 by both Rubisco and PEP case while sucrose acts as a substrate during light‐induced stomatal opening

2015; Wiley; Volume: 38; Issue: 11 Linguagem: Inglês

10.1111/pce.12555

1365-3040

Danilo M. Daloso, Werner Camargos Antunes, Daniela Pereira Pinheiro, Jardel P. Waquim, Wagner L. Araújo, Marcelo Loureiro, Alisdair R. Fernie, Thomas Christopher Rhys Williams,

Plant responses to water stress

Transcriptomic and proteomic studies have improved our knowledge of guard cell function; however, metabolic changes in guard cells remain relatively poorly understood. Here we analysed metabolic changes in guard cell-enriched epidermal fragments from tobacco during light-induced stomatal opening. Increases in sucrose, glucose and fructose were observed during light-induced stomatal opening in the presence of sucrose in the medium while no changes in starch were observed, suggesting that the elevated fructose and glucose levels were a consequence of sucrose rather than starch breakdown. Conversely, reduction in sucrose was observed during light- plus potassium-induced stomatal opening. Concomitant with the decrease in sucrose, we observed an increase in the level as well as in the (13) C enrichment in metabolites of, or associated with, the tricarboxylic acid cycle following incubation of the guard cell-enriched preparations in (13) C-labelled bicarbonate. Collectively, the results obtained support the hypothesis that sucrose is catabolized within guard cells in order to provide carbon skeletons for organic acid production. Furthermore, they provide a qualitative demonstration that CO2 fixation occurs both via ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPcase). The combined data are discussed with respect to current models of guard cell metabolism and function.