Involved in the regulation of stomatal aperture. May function as a high-capacity pump for folates. ATP + H2O + xenobioticSide 1 = ADP + phosphate + xenobioticSide 2. Inhibited by methotrexate. Ubiquitous. High expression in the guard cells. By salicylic acid (SA), menadione and, to a lower extent, by 1-chloro-2,4-dinitrobenzene (CDNB), benoxacor, cloquintocet, fenchlorazol and fluorazol. Plants have larger stomatal aperture and increased drought susceptibility, but are not affected by the ABA signal transduction pathway. Belongs to the ABC transporter superfamily. ABCC family. Conjugate transporter (TC 3.A.1.208) subfamily.