Electrotropism
Encyclopedia
Electrotropism is a kind of Tropism
which results in growth or migration of an organism, usually a cell
, in response to an exogenous electric field
. Several types of cells such as nerve cells
, muscle cells, fibroblasts
, epithelial cells
, green algae
, spores
, and pollen tubes
, among others, have been already reported to respond by either growing or migrating in a preferential direction when exposed to an electric field.
Electrotropism is known to play a role in the control of growth in cells and the development of tissues
. By imposing an exogenous electric field, or modifying an endogenous one, a cell or a group of cells can greatly redirect their growth. Pollen tubes, for instance, align their polar growth
with respect to an exogenous electric field. It has been observed that cells respond to electric fields as small as 0.1 mV/cell diameter (Note that the average radius of a large cell is in the order of a few micrometers). Electric fields have also been shown to act as directional signals in the repair and regeneration of wounded tissue.
and have a very dynamic cytoskeleton
that polymerizes at very high rates, providing the pollen tube with interesting growth properties. For instance, the pollen tube has an unusual kind of growth; it extends exclusively at its apex. Pollen tubes, as most biological systems, are influenced by electrical stimulus.
Under a constant electric field of 1 V/cm pollen tubes of Camellia japonica have been reported to grow towards the negative electrode
. Tomato and tobacco pollen tubes grew towards the positive electrode for constant electric fields higher than 0.2 V/cm. Agapanthus umbelatus pollen tubes grow towards the nearest electrode when a constant electric field of 7.5 V/cm is applied. Another report states that pollen tubes do not change growth direction under AC
electric fields.
Even though efforts have been made to clarify the mechanisms of intra- and extracellular electrical signaling in pollen tubes, the understanding of how pollen tubes react to electric fields and how the electric cue is related to the internal dynamics of pollen tube growth remains limited.
Tropism
A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus...
which results in growth or migration of an organism, usually a cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, in response to an exogenous electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
. Several types of cells such as nerve cells
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
, muscle cells, fibroblasts
Fibroblast
A fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework for animal tissues, and plays a critical role in wound healing...
, epithelial cells
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
, green algae
Green algae
The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
, spores
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
, and pollen tubes
Pollen tube
The pollen tubes is the male gametophyte of seed plants that acts as a conduit to transport the male sperm cells from the pollen grain, either from the stigma to the ovules at the base of the pistil, or directly through ovule tissue in some gymnosperms .After pollination, the pollen tube...
, among others, have been already reported to respond by either growing or migrating in a preferential direction when exposed to an electric field.
Electrotropism is known to play a role in the control of growth in cells and the development of tissues
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
. By imposing an exogenous electric field, or modifying an endogenous one, a cell or a group of cells can greatly redirect their growth. Pollen tubes, for instance, align their polar growth
Tip growth
Tip growth is an extreme form of polarised growth of living cells that results in an elongated cylindrical cell morphology with a rounded tip at which the growth activity takes place. Tip growth occurs in algae , fungi and plants Tip growth is an extreme form of polarised growth of living cells...
with respect to an exogenous electric field. It has been observed that cells respond to electric fields as small as 0.1 mV/cell diameter (Note that the average radius of a large cell is in the order of a few micrometers). Electric fields have also been shown to act as directional signals in the repair and regeneration of wounded tissue.
Electrotropism in pollen tubes
The pollen tube is an excellent model for the understanding of electrotropism and plant cell behavior in general. They are easily cultivated in vitroIn vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
and have a very dynamic cytoskeleton
Cytoskeleton
The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within a cell's cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton...
that polymerizes at very high rates, providing the pollen tube with interesting growth properties. For instance, the pollen tube has an unusual kind of growth; it extends exclusively at its apex. Pollen tubes, as most biological systems, are influenced by electrical stimulus.
Under a constant electric field of 1 V/cm pollen tubes of Camellia japonica have been reported to grow towards the negative electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
. Tomato and tobacco pollen tubes grew towards the positive electrode for constant electric fields higher than 0.2 V/cm. Agapanthus umbelatus pollen tubes grow towards the nearest electrode when a constant electric field of 7.5 V/cm is applied. Another report states that pollen tubes do not change growth direction under AC
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
electric fields.
Even though efforts have been made to clarify the mechanisms of intra- and extracellular electrical signaling in pollen tubes, the understanding of how pollen tubes react to electric fields and how the electric cue is related to the internal dynamics of pollen tube growth remains limited.