The production of the second messenger molecules diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3) is mediated by activated phosphatidylinositol-specific phospholipase C enzymes. Required for secondary responses to abscisic acid signals. a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-4,5-bisphosphate) + H2O = 1D-myo-inositol 1,4,5-trisphosphate + a 1,2-diacyl-sn-glycerol + H(+) Expressed in stems, leaves, roots, flowers and siliques. Predominant in the vascular tissues of roots and leaves. By abscisic acid, osmotic stress and environmental stresses such as dehydration, salinity and low temperature.