The insensitivity of Vinca rosea to vinblastine

Root tip mitosis in both Vinca rosea and the chosen control Lepidium sativum is susceptible to the effects of colchicine at and above 5X10(-4)M.--Root tip mitosis in L. sativum is susceptible to the effects of vinblastine at concentrations equal to and greater than 10(-4)M, while root tip mitosis in V. rosea, the plant which is the source of vinblastine, is unaffected by exogenously-applied VBL at concentrations up to and including 10(-2)M.--The possible mechanisms by which the resistance of V. rosea to vinblastine might be conferred are discussed.