Characteristics of Action Potentials in Willow (Salix viminalisL.)

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Abstract
After application of electric stimuli (square DC pulses) extra-and intracellular potentials were recorded on willow shoots. The all-or-nothing law, strength-duration relation, and general characteristics of the action potential were investigated. By using inhibitors of ionic channels (tetraethylammonium, MnCl2, LaCl3), the excitability of willow could be completely blocked. Treatment with the phosphorylation uncoupler dinitrophenol induced a depolarization and disappearance of excitability, indicating the participation of a metabolic component of the membrane potential. By using energy-dispersive X-ray microanalysis, the distribution of chloride, potassium and calcium was measured in different tissues of non-stimulated and stimulated willow shoots. It was shown that stimulation of the plant was followed by ion shifts which were most striking in the phloem cells. While their content of potassium and chloride was diminished after stimulation, the amount of cytoplasmic calcium increased slightly. These displacements lead to the conclusion that Ca2+ influx as well as K+ and Cl− efflux are involved in the propagation of action potentials.

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