PLANT PHYSIOLOGY , Vol 113, Issue 1 209-217, Copyright © 1997 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
The Propagation of Slow Wave Potentials in Pea Epicotyls
R. Stahlberg and D. J. Cosgrove
Department of Biology, The Pennsylvania State University, 208 Mueller Laboratory, University Park, Pennsylvania 16802
Slow wave potentials are considered to be electric long-distance signals
specific for plants, although there are conflicting ideas about a chemical,
electrical, or hydraulic mode of propagation. These ideas were tested by
comparing the propagation of hydraulic and electric signals in epicotyls of
pea (Pisum sativum L). A hydraulic signal in the form of a defined step
increase in xylem pressure (Px) was applied to the root of intact seedlings
and propagated nearly instantly through the epicotyl axis while its
amplitude decreased with distance from the pressure chamber. This
decremental propagation was caused by a leaky xylem and created an axial Px
gradient in the epicotyl. Simultaneously along the epicotyl surface,
depolarizations appeared with lag times that increased acropetally with
distance from the pressure chamber from 5 s to 3 min. When measured at a
constant distance, the lag times increased as the size of the applied
pressure steps decreased. We conclude that the Px gradient in the epicotyl
caused local depolarizations with acropetally increasing lag times, which
have the appearance of an electric signal propagating with a rate of 20 to
30 mm min-1. This static description of the slow wave potentials challenges
its traditional classification as a propagating electric signal.
