User:Rabia1995

Electrical signalling in plants is a plant signalling system that help them integrating internally and with the environment to coordinate molecular processes related to early development and the physiology of the adult plant.

Plants can generate different types of responses to different stimuli such as light, salt concentration, gravitropic stimulation, wounding, temperature changes. These responses are categorized as long-range electrical signals.

Researchers have been working since a very long time to understand the electrical signalling in plants and a significant progress has been made in the understanding of the basic properties of plant electrical signalling.

Types of electrical signals in plants
The different types of electrical signalling include local electrical potential (LEP), action potential (AP), variation potential/slow-wave potential, system potential (SP).

Local electrical potential
Local electrical potential is a sub-threshold response without refractory period that is induced by change in the environment. The putative ion mechanism of LEP varies from cell to cell, for example LEP in mesophyll cells during moderate light stimulation is associated with calcium influx while LEP of guard cells is mainly associated with the hydrogen, chlorine efflux and potassium influx. This signal type is local and does not propagate to other parts of the plant.

Action potential
Action potential is a short period absolute/relative refractory period electrical spike that is induced by a non-damaging stimulus. The magnitude of AP is independent of the intensity of the stimulus. The pathway of this signal is after AP is stimulated, cytosolic calcium concentration is increased leading to formation of depolarization phase and voltage gated potassium channels and anion are activated. The cytosolic potassium concentration decreases, and repolarization phase appears. Followed by decrease of cytosolic calcium concentration. Gradually, the plasma membrane returns to resting potential.

Variation potential
Variation potential/slow-wave potential is a long-term potential wave that is induced by damaging stimuli. In this type of signalling, the amplitude and duration of the potential are correlated with the intensity of the stimulus. VP can propagate over a long distance.

The ion mechanism of VP is, once the damaging stimulus is induced, mechanically sensitive/ligand dependent cation channels are activated. This makes the concentration of calcium in the cytosol to increase, and depolarization phase appears. This activates calcium dependent anion channels which leads to a decrease in the cytosolic chlorine concentration and depolarization phase is formed. Voltage-gated potassium channels are activated, and longtime repolarization phase starts. The plasma membrane gradually comes back to resting potential.

System potential
System potential is induced by a damaging stimulus like injured leaves with inorganic cation (sodium, magnesium, potassium, calcium) or glutamic acid solution. The amplitude and duration of the potential is related to the intensity of the stimulus which decreases over time. This type of signalling can propagate over long distances. The putative ion mechanism in SP is related to the activation and inactivation of the plasma membrane proton pump. The potential change is a process of hyperpolarization and then de-hyperpolarization of the plasma membrane by hydrogen ion mass efflux.

Technologies for plant electrical signal measurement
Generally, two different methods are used for measuring electric potentials in plants, extracellular and intracellular recording.

Extracellular potential measurement can be used to measure electrical potential differences over long periods of time such as several days. In higher plants, there are two types of extracellular potentials measurements, surface recording and surface measurement. Wound reaction is the basic principle used in the latter method. Upon insertion of the electrode the disruption causes the reaction that is measured in surface recordings. In case of surface measurement, this type is best used for the non-invasive and physically stable measurements.

Intracellular recording are more precise due to membrane potentials and electrical signals are likely to be deduced from specific cells. Intracellular measurements of the membrane potentials and electrical signals is mostly performed with glass microelectrodes with tip diameters of less than 1 micrometer. These electrodes are connected to a high-input impedance amplifier.