Measurement of the electrical resistance of plasmodesmata and membranes of corn suspension-culture cells

Electrophysiological investigations of intercellular communication and membrane resistance in higher plants have been hampered by the difficulty in measuring these quantities independently. Uncertainty about the position of an electrode inserted into vacuolate tissue has further complicated such measurement. To overcome these problems sister cell pairs of a Zea mays L. 'Black Mexican Sweet' suspension culture were used and dye was injected from the current-injecting electrode to determine the location of the electrode tip in each experiment. Of the impalements, 72% were cytoplasmic. The presence of plasmodesmata was fully incorporated into the electric-circuit model for the cell, and the resistance of the membrane of the current-injected cell was calculated, separate from the plasmodesmata resistance. This avoided some of the confusion resulting from work on multicellular tissue in which the position of the electrode and the extent of intercellular coupling is not determined. Using this technique, plasma-membrane resistivity was measured as 0.65 Omega . m(2), the resistivity of the tonoplast and plasma membrane in series was 1.35 Omega . m(2), and the resistance of a single plasmodesma was calculated to be 53+/-11 G Omega.