Agriculture Reference
In-Depth Information
In essence, APs are a form of electrical signaling that takes place in cells that are capable
of being excited. Note that some cells are excitable and others are not. The cells that are
excitable can produce an AP signal only if certain electrochemical conditions are met. The
emitted signal itself is a high voltage pulse, or firing that is capable of spreading far and
wide throughout the plant. They are often found to be one of the main mechanisms behind
the way plants react to various forms of stimuli including:
• Touch response, e.g. Venus Fly Trap ( Dionaea muscipula )
• Reacting to chemical compound in the soil, e.g. root exudates of nearby plants
• Insect infestation, e.g. aphids
• Phototropism, i.e. light stimulus
• Pollination events
AP Generation
Compressing the Spring 17
Under normal circumstances, the flow of ions into and out of a cell are generally equal.
This means that for all of the inflows of nutrients, there are equal outflows of waste or
reaction products that go back into the extracellular fluid surrounding the cells.
The chemical concentrations on both sides of the cell tend to be in equilibrium over time.
Electrically, due to the normal operational nature of the active transport proteins, cells tend
to favor an electronegative state. What this means is that these ion pumps often push a
larger number of positive charges (like calcium, Ca 2+ ) outside of the cell compared to the
ones that they take in, thus keeping the cell slightly more negatively charged. The effect
of this is that it's like compressing a spring, causing its potential energy to build up over
time. As larger amounts of positive charges build up around the cell wall, negative charges
accumulate on the inside of the cell walls. At this point, the cell is said to be in a state
called the negative membrane resting potential , and is measured from the inside of the cell
to the outside 18 . This build up of membrane potential (typically about -70 milliVolts) is
what's needed to prepare the cell for the creation of a signaling event known as an action
potential 19 .
Releasing the Spring
When some form of stimuli is sensed, usually by sensitive receptors that are located
throughout the outward-facing surface of the cell membrane, they create a change in
the voltage on some of the transport proteins. These transport proteins, also known as
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