Electrical membrane potential and resistance in photoautotrophic suspension cells of Chenopodium rubrum L.

On photoautotrophically grown, suspension-cultured cells of Chenopodium rubrum L. the electrical potential difference V mand the electrical resistance across plasmalemma and tonoplast have been measured using one or two intracellular micro-electrodes. In a mineral test-medium of 5.8 mM ionic strength V mvalues between 100 and 250 mV, 40% thereof between 170 and 200 mV, and a mean value (±S.E.M.) of 180.6±3.4 mV have been recorded. The average membrane input resistance R mwas 269±36 MΩ, corresponding to an average membrane resistivity r mof 3.0 Ωm(2). V mand r mare sensitive to light, temperature, and addition of cyanide, suggesting the presence of an electrogenic hyperpolarizing ion pump, and are ascribed essentially to the plasmalemma. A hexose-specific saturable electrogenic membrane channel is identified through a decrease of V mand r mupon addition of hexoses. The hexoseconcentration-dependent depolarization ΔV msaturates at 92 mV and returns half-saturating concentrations (apparent k mvalues) of 0.16 mM galactose, 0.28 mM glucose, and 0.48 mM fructose. The magnitude of V mand r mwell agrees with pertinent data from mesophyll cells in situ (where only V mdata are available) and from photoautotrophic lower plant cells. However, V mis markedly higher than reported for heterotrophically grown suspension cells of different higher plants (with which r mdata have not been reported so far). It is concluded from the present study and a companion paper on water transport (Büchner et al., Planta, in press) that photoautotrophically grown Chenopodium suspension cells closely resemble mesophyll cells as to cell membrane transport properties.