Repetitive action potentials induced in Arabidopsis thaliana leaves by wounding and potassium chloride application

A procedure (named prick-and-drop treatment) generating action potentials in the plant model Arabidopsis thaliana is described here, opening new possibilities for the analysis and understanding of the genuine nature of this phenomenon. Bioelectrical measurements were made on the petiole of the C24 ecotype with extracellular electrodes. The stimulating method includes wounding of a small area of the distal part of the leaf and subsequent addition of a drop of different kinds of solutions. The treatment inducing action potentials (APs) consists in a drop of KCl (> 0.25 M) applied on a wound, moreover the frequency of APs increased with the augmentation of the KCl concentration. Two molar sorbitol solutions were ineffective in causing APs, indicating that the effect of KCl solution is not due to the osmotic effect. Neither pricking nor addition of KCl alone caused repetitive APs (RAP), suggesting that the diffusion of the KCl solution into the apoplastic space througb the wounding area is essential. The bioelectrical responses induced with 1 M KCl consisted of 35 % of ultra-rapid APs (propagation rates > 4 mm•s-1 ). The other APs propagated at 1.7 ± 0.9 mm•s-1. Variation potentials (VPs) were also observed, and were characterised by a larger wave (longer event duration) with a slower propagation velocity (0.3 ± 0.1 mm•s-1) than the APs. A dark phase inserted during the light period led to a decrease of the amplitudes and the frequency of appearance of APs, but their velocity stayed unchanged. Our experiments demonstrate the efficiency of our method (> 90 %) to in duce spontaneous APs in A. thaliana for more than 2 h