Voltage-dependent action potentials in Arabidopsis thaliana

Voltage-elicited action potentials (APs) have been reproducibly obtained inArabidopsis 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 twogalvanically isolated Pt/Ir small wires inserted trough the main vein in the distalpart of the leaf. Conventional liquid junction Ag/AgCl electrodes were placedat the zone between leaf/petiole (e1) and a second one on the petiole, near thecentral axis of the rosette (e2). A typical hyperbolic V–t relationship wasobtained. The most excitable plants did have a chronaxy of 0.1 s anda rheobase of 2 V. Although the amplitude of the APs was highly variable (range10–80 mV), it was related neither to the intensity nor to the duration of thestimulation pulse: the phenomenon is a typical all-or-none response. The APswere moving away from the excitation zone and could successively bedetected ate1 andthenat e2:their propagationspeed was 1.15 ± 0.26 mm s21.The absolute refractory period was approximately 20 min and the relative oneapproximately 80 min. The reproducibility of the voltage elicitation was inA. thaliana col ecotype 91%, with 83% of the APs propagating from the leaf tothe petiole. In the Wassilewskija ecotype, 45% of the plants were responsive,with 78% of APs transmitted (propagation speed was 0.76 ± 0.17 mm s21),whereas in the Lansberg erecta ecotype none of the plant tested eliciteda voltage-dependent AP.