Transmission route for action potentials and variation potentials in Helianthus annuus L.

Helianthus annuus generates two types of electrical responses to different kinds of stimuli. Non-damaging electrical stimulation evokes action potentials. Damaging, thermal stimuli trigger complex responses: long lasting variation potentials with superimposed action potentials. Electrically evoked action potentials are transmitted along the stem both acro- and basipetally, and on its way, excitation covers nearly all living tissues. Action potentials usually do not enter leaves and cease in petioles. Variation potentials appearing in response to thermal stimulation of one leaf spread preferentially down the leaf trace, probably along conducting bundles. Electrodes inserted into the vicinity of conducting bundles coming from the stimulated leaf register variation potentials, while those inserted on the opposite side of the stem register no change or responses of strongly reduced amplitudes. We point out that electrode arrangement during the monitoring of the transmission of electrical signals in plants is of great importance when physiological responses of excited cells are simultaneously investigated.