Membrane Potential of Cultured Carrot Cells in Relation to the Synthesis of Anthocyanin and Embryogenesis

Membrane potentials of cultured carrot cells in culture mediumwere about –40 mV and did not change with addition ofsalts of addition (or depletion) of 2,4-dichlorophenoxyaceticacid (2,4-D). When the measurement was performed in the testmedium (containing low concentration of salts), the values werewidely distributed (from –60 to –110mV) and changedlargely with external concentration of K⁺ but not Mg²⁺ nor Ca²⁺.When the cells were fractionated by Ficoll density gradientcentrifugation, the membrane potential of the cells of higherdensity (> 14% Ficoll) was about –150 mV in the testmedium and did not change during embryogenesis with depletionof 2,4-D. The membrane potential of cells of lower density (bandingbetween 6– 10% Ficoll) was less negative (– 60 to– 110 mV) in the test medium. When these cells were transferredand cultured in medium containing zeatin but lacking 2,4-D,the membrane potential was shifted negatively by about 15 mVprior to anthocyanin synthesis. When 2,4-D was added to anthocyanin-synthesizingcells in the medium containing zeatin, a transient hyperpolarizationand subsequent depolarization of the membrane were observedprior to the inhibition of anthocyanin synthesis. (Received October 22, 1987; Accepted April 20, 1988)