Extracellular ATP Promotes Stomatal Opening of Arabidopsis thaliana through Heterotrimeric G Protein a Subunit and Reactive Oxygen Species

In recent years, adenosine tri-phosphate (ATP) has been reported to exist in apoplasts of plant cells as a signal molecule. Extracellular ATP (eATP) plays important roles in plant growth, development, and stress tolerance. Here, extracellular ATP was found to promote stomatal opening of Arabidopsis thaliana in light and darkness. ADP, GTP, and weakly hydrolyzable ATP analogs (ATPgS, Bz-ATP, and 2meATP) showed similar effects, whereas AMP and adenosine did not affect stomatal movement. Apyrase inhibited stomatal opening. ATP-promoted stomatal opening was blocked by an NADPH oxidase inhibitor (diphenylene iodonium) or deoxidizer (dithiothreitol), and was impaired in null mutant of NADPH oxidase (atrbohD/ F). Added ATP triggered ROS generation in guard cells via NADPH oxidase. ATP also induced Ca2+ influx and H+ efflux in guard cells. In atrbohD/ F, ATP-induced ion flux was strongly suppressed. In null mutants of the heterotrimeric G protein a subunit, ATP-promoted stomatal opening, cytoplasmic ROS generation, Ca2+ influx, and H 1 efflux were all suppressed. These results indicated that eATP-promoted stomatal opening possibly involves the heterotrimeric G protein, ROS, cytosolic Ca2+, and plasma membrane H+-ATPase.