Hydraulic and electrical transmission of wound-induced signals in Vitis vinifera

The nature and characteristics of the electrical response to wounding in the woody plant Vitis vinifera L. were examined. Following burning of a small area of a leaf, bioelectrical events spread throughout the shoot. The heat wound triggered stem deformations (widening–contraction), which preceded changes in biopotentials and that are interpreted as reflecting wound-induced hydraulic signals. It also caused marked decrease of extracellular resistance in stem tissues, starting about 15 s after stimulation, while intracellular resistance did not show any modification. Under an N2 atmosphere (hypoxic conditions), action potentials disappeared and the amplitude of variation potentials decreased approximately 50%. At saturating humidity variation potentials were completely eliminated, while action potentials were evident. Taken together, the results demonstrate that action and variation potentials differ both in their mechanism of propagation and electrogenic nature. Action potentials are ‘genuine’ self-propagating electrical signals travelling at a velocity of about 10 cm s-1, with a metabolic nature involving active components (electrogenic pumps). Variation potentials are a ‘local’ response to the passage of an hydraulic wave. Results support the hypothesis that both ion channels and pumps are involved in variation potential depolarisation.