Abstract
Abscisic acid (ABA) inhibits blue light-dependent stomatal opening and promotes stomatal closure under drought stress in daytime. Here we show that phosphatidic acid (PA), a second messenger of ABA signaling, inhibits the signal transduction that leads to the activation of the plasma membrane H+-ATPase in response to blue light. PA as well as ABA inhibited both the blue light-dependent stomatal opening and the H+ pumping. These ABA-mediated inhibitions were partially restored by 1-butanol, an inhibitor of PA production. PA also inhibited the blue light-dependent phosphorylation of the H+-ATPase without affecting that of phototropins, blue light receptors for stomatal opening. Furthermore, PA bound to and inhibited the protein phosphatase 1 (PP1), a positive regulator of the blue light signaling. Taken together, these results suggest that PA is involved in the ABA-mediated inhibition of blue light-dependent stomatal opening through inhibiting signaling component(s) between phototropins and the H+-ATPase, possibly PP1.