SummaryPhospholipase D (PLD) has been implicated in various processes, including signal transduction, membrane trafficking, and membrane degradation. Multiple forms of PLD with distinct biochemical properties have been described in the cell. In Arabidopsis, PLDα and PLDγ, but not PLDβ, were detected in guard cells, and antisense suppression resulted in a specific loss of PLDα. The abrogation of PLDα rendered plants less sensitive to abscisic acid and impaired stomatal closure induced by water deficits. PLDα‐depleted plants exhibited accelerated transpirational water loss and a decreased ability to tolerate drought stress. Overexpression of PLDα enhanced the leaf's sensitivity to abscisic acid. These findings provide molecular and physiological evidence that PLDα plays a crucial role in regulating stomatal movement and plant‐water status.