Spontaneous electrical activity in shoots of Ipomoea, Pisum and Xanthium

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Abstract
Extracellular recordings from light-grown shoots of Ipomoea and Xanthium contain trains of spontaneous fluctuations which resemble action potentials. The rise time of the putative action potentials is usually in the range from 1 to 50 ms. Their duration is most frequently between 100 and 400 ms, but they may be either briefer or, in the presence of unusual shoulders, much longer. Their separation interval is typically between 0.1 and 10 s. The trains may last from 1 s to over 2 h. Spontaneous fluctuations also occur individually in shoots of Ipomoea, Xanthium, and Pisum. Although the shapes, rise times, and durations of the individual fluctuations fall within the same range as do those of repetitive fluctuations, a greater number of the individual spikes have a relatively slow time course and a higher apparent amplitude. At times, recordings have periods of activity which appear to result from the superposition of numerous individual fluctuations. There is no evidence that any of the fluctuations propagate, but propagation cannot be excluded on the basis of the extracellular recordings. The fluctuations occur in both dark and light. There is no strong evidence for the occurrence of spontaneous fluctuations in roots.