Thigmotropism is a plant response to a physical stimulus.
Thigmotropism is the response of a plant to the physical contact it makes with a solid element . Due to thigmotropism, the plant adopts a certain orientation by growing on a wall or by attaching itself to a stick or rod. Even certain species have managed to develop special organs to attach themselves to the support .
Tropism is the movement that a plant makes to respond to a certain stimulus , modifying its position or orientation . According to the characteristics of the stimulus, there are different types of tropism: geotropism (caused by the force of gravity), phototropism (originating in light), hydrotropism (linked to water), etc. Thigmotropism is another of these movements.
Types of thigmotropism
It is possible to differentiate between positive thigmotropism and negative thigmotropism . Positive thigmotropism occurs when the plant in question grows around the support. Negative thigmotropism, for its part, leads the plant to avoid the solid obstacles it encounters. In the same plant, the stem can have positive thigmotropism (curling around the support) and the roots, negative thigmotropism (dodging stones).
Due to thigmotropism, the plant can adapt to the environment in different ways, altering its morphology or even modifying its growth rate. This allows it to take advantage of the structures to grow, avoid obstacles and optimize pollination, among other issues.
Tendrils are key to thigmotropism.
The tendrils
Vitis vinifera , colloquially known as vine , is a plant that has thigmotropism. This species - whose fruit is the grape - has tendrils that, when coming into contact with a support, become harder and curl, modifying the growth of the plant.
Within the field of botany , the petiole, leaf or stem that specializes in attaching one plant to another or to a specific surface is known as a tendril . Although there is a wide variety of tendrils, the most relevant are the foliar type (which are derived from leaves) and cauline (they are very thin stems that no longer have the capacity to generate flowers and leaves, since they must allow the plant to crawling or climbing).
At first glance, a tendril may look like a long vegetal-type spiral, and the direction of its rotation gives rise to the following classification: they are right-handed if they go clockwise, and left-handed if they rotate in the opposite direction. Already in the middle of the 19th century , Charles Darwin carried out an extensive study about these peculiar elements of thigmotropism, in his work entitled " On the movements and habits of climbing plants " , where he also coined the word nutation to refer to the movement of tendrils and stems when trying to find support.
Thigmotropism, a response to a stimulus
It is important to note that thigmotropism is an ability that all plants possess, although not all develop it at the same level. Climbers, for example, have specialized in it, and that is why they have achieved greater adaptation . Compared to animals, plants have a much higher sensitivity: while we can only perceive up to 0.002 mg of weight, plants can sense up to 0.0008 mg.
Within this form of response to a mechanical stimulus , we can establish groups of species according to the speed with which they react to it, and also take into account the duration of the reaction. Thigmotropism belongs to the group of plants that give a slow but lasting response when encountering another body. In climbing plants, this is easy to see, since they do not catch on from one second to the next, but once they do, they continue like this throughout their development.
The slow and short-lasting reaction is called thigmonasty , and is typical of carnivorous plants (which move as soon as an insect lands on them) and Mimosa (which folds its leaves and stems as soon as it detects a stimulus ).