Characterization of the Variation Potential in Sunflower

Abstract

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 1.) 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.

Variation potential in higher plants: Mechanisms of generation and propagation

“…First, it was shown in several studies that local damage induced changes in stem or leaf thickness that reflected hydraulic wave propagation through the plant. 4,47,53,60,61 Changes in thickness started before the electrical reaction was initiated 4,40,47,51 thus supporting their key role in VP induction. Additionally, artificially increasing xylem hydraulic pressure in the positive direction 7,49,53 induces electrical reactions that are similar to VP.…”

“…used stressor for inducing VP in a wide variety of plants, including barley, 37 faba bean, 37 soybean, 38 tobacco, 39 sunflower, 40 mimosa, 11,41,42 tomato, 6,43 Bidens pilosa, 44,45 pumpkin, 11,46 wheat, 47 and pea. 26,30,31 Mechanical injury also can induce VP.…”

Shade-Induced Action Potentials inHelianthus annuusL. Originate Primarily from the Epicotyl

“…This applies especially to signals that were induced by leaf burning. 11,[20][21][22] The easy induction of propagating electrical signals by such intrusive methods somewhat forced the conclusion that they must be "wound signals". Biochemical and molecular data seem to confirm such a view by showing that the propagation of these APs and SWPs precedes an increased production of insect-deterring proteinase inhibitors in tomato plants (e.g., refs.…”

Evaluation of the open time of calcium channels at variation potential generation in wheat leaf cells

“…The electrophysiological system plays a leading role in the coordination of wound reactions; however, little is known about its functioning. In particular, the process of variation potential generation (VP), defined as slow transitional depolarization of cell membranes extending out to the zone of local damaging irritation [1][2][3] , is poorly understood. According to the literature, variation potential is not a self-propagating signal, rather it is a local electrical reaction, induced by signal transmission from the wounded area 1 .…”

“…In particular, the process of variation potential generation (VP), defined as slow transitional depolarization of cell membranes extending out to the zone of local damaging irritation [1][2][3] , is poorly understood. According to the literature, variation potential is not a self-propagating signal, rather it is a local electrical reaction, induced by signal transmission from the wounded area 1 . The signal can be either a hydraulic wave or a chemical agent [4][5][6][7] .…”