Stomatal guard cells are the main gatekeepers for gas exchange between plants and the atmosphere, and therefore modulate the rate of photosynthesis (i.e. plant energy production) and transpiration (i.e. plant water loss). It is well known that stomatal regulation can be affected by multiple factors including abiotic and biotic stresses. During stress, rapid accumulation of GABA (γ-aminobutyric acid) in the cytoplasm can occur through the GABA shunt, which bypasses two stress-inhibited reactions of the mitochondrial based TCA cycle. Our lab’s ongoing research has shown that GABA inhibits light-induced stomatal opening and dark or ABA-induced closure in multiple species(i.e. Arabidopsis thaliana, Nicotiana bethamiana, Vicia faba and Glycine max) via the use of epidermal strip assays and gas exchange measures. However, no information has been gathered for the economically important cereals.
In order to bridge the gap, barley stomatal assays were performed using epidermal strips bathed in solution and exposed to opening and closing stimulus (ABA at a range of concentrations and during light/dark transitions) with the presence and absence of GABA. Here, low concentration of GABA did not elicit stomatal movement by itself but inhibited light-induced stomatal opening and dark or ABA-induced closure. Interestingly, a high concentration of GABA led to a greater degree of closure during both ABA exposure and light/dark transitions. Results of leaf-feeding assays showed similar outcomes. The ultimate aim of this project is to identify how modification of GABA responses in barley might be used to improve water use efficiency and stress tolerance in cereal crops.