Voltage-dependent action potentials in Arabidopsis thaliana

Voltage-elicited action potentials (APs) have been reproducibly obtained in Arabidopsis thaliana ecotype col. Excitations pulses (voltage-duration: V-t) were given in the 0- to 18-V and 0- to 35-s ranges, respectively, by two galvanically isolated Pt/Ir small wires inserted trough the main vein in the distal part of the leaf. Conventional liquid junction Ag/AgCl electrodes were placed at the zone between leaf/petiole (e1) and a second one on the petiole, near the central axis of the rosette (e2). A typical hyperbolic V-t relationship was obtained. The most excitable plants did have a chronaxy of 0.1 s and a rheobase of 2 V. Although the amplitude of the APs was highly variable (range 10-80 mV), it was related neither to the intensity nor to the duration of the stimulation pulse: the phenomenon is a typical all-or-none response. The APs were moving away from the excitation zone and could successively be detected at e1 and then at e2: their propagation speed was 1.15 +/- 0.26 mm s(-1). The absolute refractory period was approximately 20 min and the relative one approximately 80 min. The reproducibility of the voltage elicitation was in A. thaliana col ecotype 91%, with 83% of the APs propagating from the leaf to the petiole. In the Wassilewskija ecotype, 45% of the plants were responsive, with 78% of APs transmitted (propagation speed was 0.76 +/- 0.17 mm s(-1)), whereas in the Lansberg erecta ecotype none of the plant tested elicited a voltage-dependent AP.