Pairs of guard cells form stomatal pores through which gas exchange occurs.Gas exchange includes transpirational water loss,and guard cell signaling in drought response has been studied for decades.Abscisic acid (ABA) is the major hormone that regulates drought responses.ABA and other metabolites can be synthesized in one cell type or subcellular compartment and transported across membranes by specific transporters to conduct biological functions.Two new papers,both taking advantage of reverse genetic methods,one focusing on a plasma membrane ABA efflux carrier (Zhang et al.,2014) and the other on a putative mitochondrial pyruvate carrier (Li et al.,2014),have recently shown the importance of metabolite transporters in ABA function and guard cell response.