Kinetin-Induced Stimulation of Electrogenic Pumping in Soybean Suspension-Cultures is Unrelated to Signal Transduction

Primary modes of action of cytokinins have been thought to involve stimulation of the electrogenic H+ pump and-or opening of plasmamembrane Ca2+ channels. In order to test these hypotheses, rapid changes in membrane transport in response to cytokinin application were studied in heterotrophic suspension-cultured callus of soybean (Glycine max (L.) Merr.) using electrophysiological techniques. Kinetin (N6-furfurylaminopurine; 2 μM) elicited membrane hyperpolarization of 13±1 mV. This effect occurred even at membrane poteintials more negative than the most negative ionic equilibrium potential, and therefore might have resulted either from stimulation of the electrogenic pump, or from closure of ionic channels. The former mechanism of action appears most likely because (i) kinetin-induced membrane hyperpolarization is not accompanied by a significant change in plasma-membrane resistivity and (ii) hyperpolarization is abolished by cyanide, which inhibits electrogenic pump activity by depletion of cellular ATP.