Characteristics of Action Potentials in Willow (Salix viminalis L.)

After application of electric stimuli (square DC pulses) extra-andintracellular potentials were recorded on willow shoots. Theall-or-nothing law, strength-duration relation, and generalcharacteristics of the action potential were investigated. Byusing inhibitors of ionic channels (tetraethylammonium, MnCl₂,LaCl₃), the excitability of willow could be completely blocked.Treatment with the phosphorylation uncoupler dinitrophenol induceda depolarization and disappearance of excitability, indicatingthe participation of a metabolic component of the membrane potential.By using energy-dispersive X-ray microanalysis, the distributionof chloride, potassium and calcium was measured in differenttissues of non-stimulated and stimulated willow shoots. It was shown that stimulation of the plant was followed by ionshifts which were most striking in the phloem cells. While theircontent of potassium and chloride was diminished after stimulation,the amount of cytoplasmic calcium increased slightly. Thesedisplacements lead to the conclusion that Ca²⁺ influx as wellas K⁺ and Cl^– efflux are involved in the propagation ofaction potentials. Key words: Action potential, electrical stimuli, energy-dispersive X-ray microanalysis, ion shifts, Salix viminalis