Action and resting potentials were measured in potato plants (Solanum
tuberosum L.) under different physiological conditions. External stimu
li (e.g., raising the temperature, mechanical wounding, exposing plant
leaves or soil to certain chemical compounds) caused action potential
generation and lead to shifting the resting potential from its origin
al steady-state level. The amplitude, polarity, and propagation veloci
ty of action potentials depended on the type of external stimulus or s
tress. The kinetics and amplitude of resting potential changes also de
pended on the nature of external stimuli. In plants invested with leaf
-feeding larvae of the Colorado potato beetle (Leptinotarsa decemlinea
ta), the insect-induced action potentials moved downward along the ste
m with a velocity of about 0.05 cm/s. The action potentials propagated
downwards from the damaged leaf to the roots. When the upper leaves o
f potato plants were sprayed with 0.3 ml of 1 mM pentachlorophenol aqu
eous solution, the effect was nearly identical to that induced by Colo
rado potato beetles.