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. Nondamaging electrical stimulation evokes action potentia ls. Damaging, thermal stimuli trigger complex responses: long lasting varia tion potentials with superimposed action potentials. Electrically evoked ac tion potentials are transmitted along the stem both acro- and basipetally, and on Its way, excitation covers nearly all living tissues. Action potenti als usually do not enter leaves and cease in petioles. Variation potentials appearing in response to thermal stimulation of one leaf spread preferenti ally down the leaf trace, probably along conducting bundles. Electrodes Ins erted into the vicinity of conducting bundles coming from the stimulated le af 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 tran smission of electrical signals in plants is of great importance when physio logical responses of excited cells are simultaneously investigated.