Key words: GABA, ABA, stomatal movement, drought
Stress negatively impacts plant growth and development, reducing plant productivity. The movement of stomata, which are pores surrounded by pairs of guard cells, is controlled by cellular signals, and is important for plants adaptation to biotic and abiotic stresses. GABA (γ-aminobutyric acid) is a stress-induced metabolite in plants. Its metabolism is important for maintaining energy production, for ROS detoxification, pH balance, as a C/N source and osmolyte. GABA is mainly synthesized via Glutamate Decarboxylase (GAD). There are 5 GAD genes identified in Arabidopsis, (GAD1-5). Previous publications have indicated that only GAD1, GAD2 and GAD4 expression was detectable in Arabidopsis shoots, with GAD2 the major isoform. Here, we find that mutation of GAD2 causes higher stomata conductance and intolerance to drought. However, a tetraploid mutation of GAD1, GAD2, GAD4 and GAD5 (gad1/2/4/5) showed a similar stomata aperture to wild type (WT) plants under both standard and drought conditions. Thus, GABA regulation of stomatal movement does not follow a simple dose-response relationship. Abscisic acid (ABA), a stress induced hormone in plants, retains water content of plants under drought by closing stomata. However, this effect of ABA is impaired on gad1/2/4/5 under drought. Thus GABA may play a role in controlling stomatal movement under both normal and stress conditions. Future work, will aim to understand the basis for GABA and ABA signalling interactions in the control of stomatal movement including the effect on transcriptional regulation.