A biological phenomenon that indicates growth or turning movements in plants due to the influence of the environment is termed tropic movement in plants or tropism in plants.
In English, the word tropism means an action done in a very unthoughtful manner. But here tropism is a very directional process. In general, tropism is described as 3 step process which includes
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sensation to a stimulus, as a living being, it becomes a beneficiary factor for the plants.
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Signal transduction occurs( in simple words, the environment reaction towards the plant)
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And finally, the directional growth response takes place.
These are the following steps that give rise to tropism or what we call “tropic movements in plants”.
Tropism is seen not only in plants but also in viruses, pathogens and other biological organisms also. This phenomenon is direction-dependent and reacts according to the direction of the stimulus. Other types of tropism in different organisms are also called host tropism, tissue tropism or cell tropism.
Types of Movements in Plants
In plants, there are five types of tropic movements. These tropic movements can be explained as described below:
Phototropism
sunlight is a major source that helps plants to sustain life. This type of tropism in plants occurs due to the response to lights. In general, the plants will grow in the direction of light. It can be positive if the reaction is towards the light and it can be negative if the reaction is away from light.
Geotropism
When plants show movement in the direction of gravity the roots will grow downwards and hence shows positive geotropism. Similarly, if its shoots will grow upwards, then the process can be defined as negative geotropism.
Chemotropism
Apart from the environmental factors, there are some chemical factors also which involve the tropic movements. The movement in seed plants while transferring pollen grains to the female gamete releases some chemicals; this process leads to positive chemotropism.
Hydrotropism
When the movement of plants occurs due to the stimulus of water then the phenomenon is termed hydrotropism. This process leads to roots growing towards the area where water is present.
Thigmotropism
The movement of reflex of a plant takes place in response to touch gives rise to thigmotropism. A very common example of this kind of tropism occurs in the touch me not plant. As soon as one touches the leaves of this particular plant they droop.
In the case of phototropism or geotropism (also known as gravitropism), directional growth occurs due to the asymmetric distribution of the chemical substance known as “Auxin”.
Tropism in plants is a process of growth of the plant shoots and roots in accordance with the natural environment surrounding it.