Electrical characteristics of cells from leaves of Lycopersicon

Abstract

Microelectrode techniques were used to investigate the electrical properties of leaf cells of Lycopersicon esculentum both in excised leaflets and in small tissue sections. Most of the recordings were from epidermal cells of the abaxial midrib.Cells were electrically coupled. Apparent resistivity was lowest shortly after impalement (mean value about 1.8 kΩ cm−2) and increased gradually during most experiments. A fluctuation of resistance and potential occurred during the first 5–10 min of many recordings.Potentials between the vacuole and external medium averaged about −125 mV in all preparations, regardless of the external K+ content. Vacuolar K+ activity averaged about 66 mM. The average Nernst potential for K+ would thus be only about −48 mV for an external concentration of 10 mM. Changes of external pH between 5.6 and 8.6 had little or no effect on the potential, but at 4.6 the cells depolarized to about −50 mV and required about 2 h to recover after the pH was raised to 6.6. The potentials were partially dependent on metabolic activity, since CN− or CN− and SHAM together caused marked depolarization.Darkening and illuminating leaf mesophyll cells elicited reproducible transients; associated with the transient light-induced depolarization was a 10–15 mV spike. Changes in illumination had extremely variable effects on the potential of midrib epidermal cells.