Hydrolyzes glycerol-phospholipids at the terminal phosphodiesteric bond to generate phosphatidic acids (PA). Plays an important role in various cellular processes, including phytohormone action and response to stress, characterized by acidification of the cell. a 1,2-diacyl-sn-glycero-3-phosphocholine + H2O = a 1,2-diacyl-sn-glycero-3-phosphate + choline + H(+) Ca(2+) requirement for activity depends on pH. Active either under acidic conditions with micromolar levels of calcium (PIP2-dependent) or at neutral pH with millimolar levels of calcium (PIP2-independent). Found in vacuoles and also associated with plasma, microsomal and mitochondrial membranes and in clathrin-coated vesicles. Not found in chloroplast or nuclei. Activation increases association of preexisting enzyme with membranes. The distribution of this conventional PLD between membrane-associated and soluble fractions varied from organ to organ and is calcium-regulated. Highly expressed in roots, stems and flowers, moderately in leaves, seedlings and siliques. Not detected in dry seeds. Activated by abscisic acid (ABA), ethylene, heavy metal, cold, salt and osmotic stresses. C2 domain is a calcium-binding fold, and the binding promotes the protein association with membranes. A lower affinity toward calcium can be anticipated for PLD alpha due to the absence of two potential calcium ligands. Belongs to the phospholipase D family. C2-PLD subfamily.