SPONTANEOUS OSCILLATIONS OF EXTRACELLULAR ELECTRICAL POTENTIALS MEASURED ON LEPIDIUM-SATIVUM L ROOTS

Electrical potential differences (PDs) were measured continuously at six points in line on the surface of primary roots of cress (Lepidium sativum L.). The root-to-hypocotyl transition was used as the reference. A gradient of extracellular potentials existed along the root axis. The most negative potentials were observed at the root tip. Whenever the growth rate declined to 0.10 mm h-1 or less, the PDs were nearly constant in space and time. Otherwise, the PDs showed different types of changes with time. Roots with growth rates between 0.65 and 1.10 mm h-1 preferably showed PDs characterized by approximately sinoldal oscillations. Maximal amplitudes appeared in the middle of the elongation zone. Roots which were exposed to a N2-atmosphere exhibited a reversible disappearance of the electrical oscillations and a decrease in the PD-gradient. Similar effects were obtained by the application of the metabolic inhibitor azide (N3). These results proved that the electrical oscillations are dependent on the aerobic cell metabolism.