Phosphatidylinositol 4,5-bisphosphate - Phospholipase C activity during the growing phase of Catharanthus roseus transformed roots

A phosphatidylinositol 4,5-bisphosphate phospholipase C (PLC) activity was identified in different tissues from Catharanthus roseus. The specific activity of the enzyme was 10 times higher in a membrane fraction that in cytosol. During a culture cycle, in two different root lines, PLC-activity in the cytosol reached a maximum that preceded the higher activity in the membranes. Both activities, soluble and membrane, are calcium-dependent for full activity. The membrane-bound activity catalyses efficiently phosphatidylinositol 4,5 bisphosphate (PIP2) and phosphatidylinositol 4-monophosphate (PIP) hydrolysis while phosphatidylinositol (PI) is a poor substrate. The soluble activity preferentially hydrolyzed PI over PIP and PIP2. Both activities are completely inhibited by Triton X-100, whereas they respond differentially to n-octyl beta-D-glucopyranoside.