PLANT PHYSIOLOGY , Vol 115, Issue 3 1083-1088, Copyright © 1997 by American Society of Plant Biologists
|
WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Characterization of the Variation Potential in Sunflower
B. Stankovic, T. Zawadzki and E. Davies
School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588 (B.S., E.D.)
A major candidate for intercellular signaling in higher plants is the
stimulus-induced systemic change in membrane potential known as variation
potential (VP). We investigated the mechanism of occurrence and
long-distance propagation of VP in sunflower (Helianthus annuus L.) plants.
Here we present evidence of the relationship among injury-induced changes
in xylem tension, turgor pressure, and electrical potential. Although
locally applied wounding did trigger a change in membrane potential, it
evoked even faster changes in tissue deformation, apparently resulting from
pressure surges rapidly transmitted through the xylem and experienced
throughout the plant. Externally applied pressure mimicked flame wounding
by triggering an electrical response resembling VP. Our findings suggest
that VP in sunflower is not a propagating change in electrical potential
and not the consequence of chemicals transmitted via the xylem, affecting
ligand-modulated ion channels. Instead, VP appears to result from the surge
in pressure in the xylem causing a change in activity of mechanosensitive,
stretch-responsive ion channels or pumps in adjacent, living cells. The
ensuing ion flux evokes local plasma membrane depolarization, which is
monitored extracellularly as VP.
