An example of negative thigmotropism is the growth of roots underneath the soil. When an elongating root comes into contact with an object, e.g., a rock, it grows away from the object. The drooping of leaflets of Mimosa pudica when touched is not considered thigmotropism but a nastic movement. Thigmotropic growth is usually limited to soil or other substrates that do not support normal plant growth.
Thigmotropy is the tendency of some organisms to grow toward moist or juicy tissues. Thigmotrophic fungi and bacteria live in or on dead organic matter such as wood or manure and use its moisture content for growth and reproduction. Without such material to feed on, they would die after a few days or weeks. Some species of algae are also thigmotropic. In this case, the term is used to describe their preference for growing in shallow waters near shoreline vegetation where there is sufficient light for photosynthesis but not so much water that it is life-threatening if they lose control of their position by floating away.
Thigmotropism is the opposite of hydrotropism, which is the tendency of plants to grow toward moisture. Thigmotrophic fungi and bacteria lack the hydro signals that allow most plants to grow toward water. Instead, they find their way to moisture by feel alone because there are no physical cues available to guide them.
Thigmotrophy is the only method that certain organisms use to obtain nutrients from their surroundings.
Positive thigmotropism may be seen in the development of ivy on walls when it comes into touch with walls and the curling of vines or twins when they come into contact with things for support. The subterranean development of roots is an example of negative thigmotropism. Roots will not grow in loose soil, but must find something solid to anchor themselves to. They do this by growing inward toward a source of water such as a well or stream.
Thigmotropic organisms have evolved strategies to find or make their way using only their senses of touch and smell because exploration through vision or hearing would be too dangerous or costly. Thigmotrophy is a common trait among fungi, algae, some bacteria, and some plants. Fungi use their tendrils to search for food or mates, while algae and some bacteria migrate toward light or nutrients by extending filaments that respond to these stimuli.
Some plants exhibit thigmotropy, especially grasses. When young shoots reach the surface of the ground, they send out long tendrils that can attach themselves to objects such as an animal's fur or clothing. Once attached, the shoot grows upward toward sunlight so that more photosynthetic activity can occur. This is why uncultivated land often has a patchy appearance: Some areas are covered in grass, while others aren't and remain bare because the grass finds it difficult to grow there due to the lack of sunlight.
A positive thigmotropism is a reaction to the touch stimulus, whereas a negative thigmotropism is a reaction to the opposite stimulus. The proliferation of roots under the earth is an example of negative thigmotropism. The development of branches on trees is an example of positive thigmotropism.
Thigmotropic organisms have evolved mechanisms to detect when they come in contact with their environment, which includes members of their own species as well as other objects in their surroundings. This initial sensory detection event leads to changes inside the organism that prepare it for further interaction with its environment. These changes can include alterations in gene expression, cell division, or tissue growth/remodeling. For example, when plants feel the touch of water, the perception of moisture leads to changes in gene expression that help the plant grow deeper roots. Roots growing closer to the surface would be at a disadvantage because they would be more likely to encounter drying out again before they could absorb enough water from their environment to survive.
How do plants know how to react to a touch stimulus? During evolution, plants who grew their roots closer to the surface than their competitors were likely to find food and water, which allowed them to proliferate and pass their genes along more often. As a result, plants with shallow roots did not have an advantage over those with deep ones.
The coiling movement of tendrils in the direction of an item that they contact is an example of thigmotropism. The folding action of the Mimosa pudica leaflets, on the other hand, is an example of thigmonastism. Leaves of this plant roll up when disturbed.
Thigmotropic organisms have organs that will bend toward something that contacts them. Thigmotropic plants usually have sticky hairs or bristles that help them attach to surfaces. Thigmotropic animals often have tentacles or feelers that can be used to detect heat, moisture, or chemical signals in the environment. They may also have limbs that can be used for exploring their surroundings. Plants and animals, respectively, that exhibit thigmotropic growth are called thigmotactic.
In physics, stress is the force per unit area acting on a body to cause it to change shape. If the force is applied uniformly throughout the body, then the term uniform stress is used. Stress can be divided into two types: mechanical and non-mechanical. Mechanical stress results from applying forces directly by hand. Non-mechanical stress results from interactions with other objects or substances; for example, water exerts pressure on the surface of a glass bottle, causing it to deform. Mechanical stresses decay over time while non-mechanical stresses remain constant until some external factor intervenes.
Roots, in general, have a negative touch reaction, which means that when they contact an item, they will grow away from it. This permits the roots to go through the soil with as little resistance as possible. Roots are believed to be negatively thigmotropic as a result of this activity. That is, roots will move away from any object that is touching or near touching them.
Thigmotropism is different from nastiness because roots will not only move away from objects that are touching or near touching them, but they will also grow toward moist or dry areas of the soil. Thus, thigmotropism is a natural response by roots to try and find the best position in which to grow into the earth. Without thigmotropism, roots would be forced to stay in one place, which could cause problems for the plant if environmental conditions change over time.
Thigmotropy is different from neophobia (fear of novelty) because plants do not fear certain stimuli such as water or heat. They may avoid some situations because it is safer to do so, but this does not mean that they are afraid of those things. For example, if a plant is growing in water, it is still able to sense light changes and other sensations from the environment without being affected by them.
Plants show thigmotropy towards textures that are smooth, soft, or slightly elastic.
Positive thigmotropism includes the growth of ivy on walls in response to touch with walls and the coiling of tendrils or twiners in response to contact with objects for support. The term "thigmotropic" means "caused by touch." This phenomenon is common among plants and can be beneficial or detrimental depending on the plant species involved.
For example, when an infant is exposed to the smoke from burning incense, it will likely suffer from bronchitis as well as asthma. The reason is that the smoke causes its lungs to react with thigmotropism, i.e., it lunges toward air flow like vines do when touched. This behavior is natural and necessary to prevent the child from breathing in more smoke. But because of this habit, the baby's lungs are weakened and become dependent on air flow for oxygenation which makes them vulnerable to further damage caused by smoke.
Plants exhibit thigmotropism too. When a seedling first emerges from the soil, it is fragile and needs all its resources for growth so it reacts negatively to physical contact. If it is grasped by another plant or something else falls on it, this will most likely cause death since the seedling cannot allocate its resources to growing roots if they are already used up through active defense mechanisms.