The relative electrical resistances of the plasmalemma and tonoplast in higher plants.

Measurements on 3-6 days old root hair cells of cucumber, oats and maize, in a medium of 1.0 mN KCl plus 1.0 mN CaCl2, gave an average d.c. surface resistance value of 3,000 ohm·cm(2) for the plasmalemma and of 3,500 or 3.600 ohm·cm(2) for the plasmalemma and tonoplast in series. The average value for the combined surface resistance of the two membranes was about 1.2 times that of the plasmalemma alone, showing that in the above cells the latter membrane has a resistance appreciably more than that of the tonoplast.It is concluded that the plasmalemma offers a major barrier to the passive uptake of ions. This conclusion is supported by a consideration of transverse impedance measurements of young and old tissues.