Mechanisms of Plant Electrophysiology - Electro-Horticulture - page 74

Source: Based on (Taiz, 2002)
Passive Transport
Passivetransport , orthetransportofmaterialsacrossthecellboundaryfromanareaofhigh
concentration to an area of low concentration, can be accomplished via simple diffusion
(described above), or using a method called facilitated diffusion that occurs via transport
proteins embedded within the cell membrane.
In facilitated-diffusion, protein structures called channel or carrier proteins are used to
facilitate transport across the membrane. These proteins, also called voltage-gated
channels , can handle not only individual ions, but larger molecules as well. Furthermore,
they act as voltage sensors in that they change shape is response to electrical signals. This
change in shape is what enables the passage of complex molecules to flow through them.
In fact, I would say that it's this one particular physiological organ, the voltage-gated
channel, that is the reason why electroculture works. It is the enabling response that
ultimately leads to chain reactions that bring about beneficial changes throughout the
plant.
Note that portions of the membrane are permeable to only a subset of all of the possible
ions that may be available in its environment, e.g. potassium ions or chloride ions. The
cell membrane acts as a gatekeeper. These channel proteins are capable of selectively
allowing(viasubstance-leveldetectorsorvoltage-controlsignals)somesubstancestoenter
whilesimultaneouslyexcludingothers.Theyrespondnotonlytochemicalsignals,butalso
electrical ones as well that specify which ions are allowed to pass. Once the protein is told
to pass a certain type of substance, it can allow a very large volume of it to pass through.
Cell membranes can have varying degrees of electric potential between their internal and
external portions. Whenever there is a membrane potential, which in this case occurs from
a buildup of similarly charged atoms and molecules on one side or the other, the result is
a flow of electric charge if the barriers are open. So, when electrical current is blocked
in some way, a voltage (also known as potential difference) builds up across the blocking
element and the relative portions of the cell wall.
Similar to the voltage difference that can be measured across two different parts of a circuit, in biology,
the differences in charge across the cell boundary can be measured as an electric potential difference.