RAPID CHANGES IN THE ENZYME-ACTIVITIES AND METABOLITES OF THE PHOSPHATIDYLINOSITOL-CYCLE UPON INDUCTION BY GROWTH-SUBSTANCES OF AUXIN-STARVED SUSPENSION CULTURED CATHARANTHUS-ROSEUS CELLS

Suspension cultured Catharanthus roseus cells grown with 2,4-dichlorophenoxyacetic acid (2,4-D) were starved for this growth substance for 3 days, thereafter cell proliferation was induced by addition of 2,4-D, kinetin, or alpha-napthaleneacetic acid (alpha-NAA) and kinetin. In one set of experiments changes of H-3-inositol-labeled phosphoinositides and inositol phosphates were determined in a time interval of 15 min after induction. In a second set of experiments the activities of phosphatidylinositol(PI)-kinase and diacylglycerol (DG)-kinase were followed by the use of [gamma-P-32]ATP. Induction by 2,4-D revealed a very fast maximum 1 min after addition of the growth substance) increase in Insl,4P2, decrease in PIP and increase in PI-kinase activity. Addition of alpha-NAA and kinetin resulted in a very fast decrease of PI and PIP (1 min after induction) and a concomitant decrease in the activities of PI-kinase and DG-kinase, whereas slightly slower (2 min after induction) but very strong increases in InslP1 and Insl,4P2 were observed. Although obtained with an artificial in vitro system, these results demonstrate that the activities of the PI-cycle are responsive towards phytohormones.