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Hydrolysis of common membrane phospholipids occurs in response to various environmental stresses, but the control and cellular function of this hydrolysis are not fully understood. Hydrogen peroxide (H[sub2]0[sub2]) is a pivotal signaling molecule involved in various stress responses. Here, we show that the plasma membrane-bound phospholipase D, PLDδ, is activated in response to H[sub2]0[sub2] and that the resulting phosphatidic acid (PA) functions to decrease H[sub2]O[sub2]-promoted programmed cell death. The Arabidopsis genome has 12 PLD genes, and knockout of PLDδ abolishes specifically the oleate-stimulated PLD activity. H[sub2]O[sub2] treatment of Arabidopsis cells activates PLD enzyme activity, and ablation of PLDδ abolishes that activation. PLDδ-null cells display increased sensitivity to H[sub2]O[sub2]-induced cell death. The addition of PA to PLDδ-null cells mitigates the H[sub2]O[sub2] effect, whereas suppression of the H[sub2]O[sub2]-induced PA formation in wild-type cells increases the effect. PLDδ-ablated plants exhibit increased susceptibility to stress. These results demonstrate that activation of oleate-stimulated PLDδ constitutes an important step in the plant response to H[sub2]O[sub2] and increasing plant stress tolerance. [ABSTRACT FROM AUTHOR]