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

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Abstract
On photoautotrophically grown, suspension-cultured cells of Chenopodium rubrum L. the electrical potential difference Vmand 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 Vmvalues 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 Rmwas 269±36 MΩ, corresponding to an average membrane resistivity rmof 3.0 Ωm2. Vmand rmare 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 Vmand rmupon addition of hexoses. The hexoseconcentration-dependent depolarization ΔVmsaturates at 92 mV and returns half-saturating concentrations (apparent kmvalues) of 0.16 mM galactose, 0.28 mM glucose, and 0.48 mM fructose. The magnitude of Vmand rmwell agrees with pertinent data from mesophyll cells in situ (where only Vmdata are available) and from photoautotrophic lower plant cells. However, Vmis markedly higher than reported for heterotrophically grown suspension cells of different higher plants (with which rmdata 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.