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

Abstract 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 α-naphthaleneacetic acid (α-NAA) and kinetin. In one set of experiments changes of 3 H-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 [γ- 32 P]ATP. Induction by 2,4-D revealed a very fast (maximum 1 min after addition of the growth substance) increase in Ins1,4P 2 , decrease in PIP and increase in PI-kinase activity. Addition of α-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 Ins1P 1 and Ins1,4P 2 were observed. Although obtained with an artificial in vitro system, these results demonstrate that the activities of the PI-cycle are responsive towards phytohormones.