Mechanisms of Plant Electrophysiology - Electro-Horticulture - page 78

voltage-gated channels (VGCs) , can be electrically controlled; therefore, they can be
programmed to open and close in response to changes in voltage, similar to the way an
electromechanical relay works like the one in your car door (controlling the door locks).
A small amount of control voltage (e.g. from the switch) is used to control the flow of a
larger amount of current (e.g. the current needed to move the door locks). When the ionic
charge levels meet a certain threshold voltage, also known as an amplitude window 20 , they
cause the various VGCs to change state. The reason the term amplitude window is used is
because it represents a range of amplitudes, or voltage levels that may be what's needed to
open the ion channels, all depending upon the type of ion channel, the tissue type and the
plant species.
Once the receptors are sufficiently stimulated, they cause the channel proteins to open up,
lettingcalciumionsinfromthecell'sextracellularfluid.Sincecellsarenormallyoperating
in a negative charge environment, when the gates open, a flood of positive ions enters the
cell's interior - not only because there is a buildup of charge concentration on the outside
near the gate, but also because like-charges repel each other. These repelling charges then
push each other away, into the channel protein, and out of the other side, into the cell.
So, when these charges flood into the cell, it changes the amount of calcium concentration
within the cell. The amount of change, as well it's location within the cell, has an effect
on the response 21 . Differences in calcium levels are called calcium signatures 22 and play a
part in the physiological response mechanism of the plant.
Schematic Illustration of an Action Potential
Source: Wikipedia
Once inside, this mass of positive charge spreads abou t 23 and causes what's called cellular
depolarization , or a reversal of the polarity within the cell. At first the cell's interior was