Abstract
A phytohormone, abscisic acid (ABA) induces stomatal closure to reduce transpirational water loss via a fine-tuned signal transduction in guard cells. In this study, we report that gene disruption of an Arabidopsis histidine kinase, AHK5 causes ABA hypersensitivity of guard cells. In the ahk5-1 mutant, ABA-induced stomatal closure was enhanced. We investigated plasma membrane ion channel activities of the ahk5-1 mutant guard cells using a patch clamp technique. Changes of cytosolic free calcium concentration in guard cells were also monitored using a fluorescent calcium indicator, yellow cameleon 3.6. The results suggest that AHK5 functions as a negative regulator of ABA signaling in Arabidopsis guard cells.
