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The notion of tropism it is used in the biology to name the displacement who do the plants or certain organs of them to respond to a stimulus It comes from outside.

There are different kinds of tropisms according to the nature of the stimulus. When the reaction of the plant is caused by the force of gravity and its acceleration, we talk about gravitropism . The roots, in this case, grow towards the ground while the stems develop upwards until they surface. It is said that the root tropism is positive (accompanies the force of gravity), while the tropism of the stems is negative (opposite to the mentioned force).

Due to the phototropism , the plants react to the light , which allows the development of the photosynthesis . Unlike what happens with gravitropism, in this case the roots exhibit a negative phototropism and the stems have a positive phototropism. Within the phototropisms, the heliotropism : the tropism that implies a movement of the plant according to the orientation of the Sun .

Other kinds of tropisms are those recognized as part of the chemotropisms , which are linked to plant responses to chemical elements. When these elements are beneficial to the plant organism, the motorcycling (the stems are oriented to the aerated regions of the surface) or the hydrotropism (They go to the water).

When contacting a solid Finally, plants can develop the tigmotropism , a reaction that produces a modification in its growth. This type of tropism is the one made by climbing vegetables.

Tissue tropism

In virology, the branch of microbiology that studies virus , talk about tissue tropism to refer to the affinity that a given virus has with one or more tissues of its host (also called host). Some of the factors that influence its distribution are the following: how susceptible the host is; that there are recipients of the virus in question in the host organism; the virus reproduction rate (this cycle is also known as viral replication).

Tissue tropism can also occur or increase due to the presence of soluble proteins or cytokines (also known as cytokines, are proteins that are responsible for regulating the functioning of certain cells and their communication, among other tasks) that counteract the action of the host. It is worth mentioning that this phenomenon can also favor developing of bacteria, and that the affinity can be to a particular tissue or to a large number of different tissues and cells.

A clear example of tissue tropism occurs in porcine adenovirus type 3, which is similar to columnar epithelial cells. Similarly, bovine adenovirus is attracted to capillary endothelial type cells. The rabies virus, meanwhile, has an almost exclusive affinity to tissue neuronal

Cellular receptors are known to proteins found in cells and they have the power to allow fusion with a virus cell. Through the process of tissue tropism, the form that these proteins acquire is comparable to that shown during an infection.

Some of the stages that are identified throughout tissue tropism are the following:

* the virus enters the organism ;
* their cells fuse with others;
* a process known with the name of reverse transcription, which consists in generating double stranded DNA from a single stranded RNA;
* virus particles sprout and acquire the necessary tissue to continue tropism.

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