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 spe cific activity of the enzyme was 10 times higher in a membrane fractio n that in cytosol. During a culture cycle, in two different root lines , PLC-activity in the cytosol reached a maximum that preceded the high er activity in the membranes. Both activities, soluble and membrane, a re calcium-dependent for full activity. The membrane-bound activity ca talyses efficiently phosphatidylinositol 4,5 bisphosphate (PIP2) and p hosphatidylinositol 4-monophosphate (PIP) hydrolysis while phosphatidy linositol (PI) is a poor substrate. The soluble activity preferentiall y hydrolyzed PI over PIP and PIP2. Both activities are completely inhi bited by Triton X-100, whereas they respond differentially to n-octyl beta-D-glucopyranoside.