Some plants close up when touched due to a phenomenon called thigmomorphogenesis, an adaptive response that allows the plant to protect itself from predators or unfavorable environmental conditions.
When certain sensitive plants like Mimosa pudica are touched, a small electrical signal is triggered. This signal spreads very quickly through the leaves. This impulse causes a cascade of internal movements, leading to the rapid release of water from the cells. The result? The cells lose part of their internal pressure, called turgor pressure. Without this pressure, the leaves immediately fold in on themselves. It's a bit like a balloon deflating when it's pierced. In just a few seconds, the leaves are closed and appear dead; yet everything is fine, it's simply a reversible strategy controlled by the plant itself.
Plants do not have muscles or nerves like animals, but they still respond to touch through a phenomenon called thigmonasty. This phenomenon generally relies on a rapid change in water pressure within specialized cells located at the base of leaves or leaflets. When the plant feels physical contact, these cells quickly lose their water, relax, and cause a closing movement. This very rapid response allows plants to protect themselves against predators or certain physical damage. Touch generates a kind of electrical signal in plant tissues, similar to a small temporary electric current observed in animals. This triggers a whole series of chemical reactions leading to the rapid movement of the leaves.
The most famous plant for this kind of behavior is surely the Sensitive (Mimosa pudica). You barely touch it with your fingertips, and bam, the leaves instantly fold up. Another cool plant is the Venus flytrap (Dionaea muscipula): when an insect brushes against its tiny hairs, its trap leaves snap shut in a flash to capture their snack. Carnivorous plants of the genus Drosera, known as sundews, are also reactive: their leaves covered in sticky hairs move slowly to trap the insect that comes to stick to them. Finally, some aquatic plants, like Utricularia, use ultra-fast suction traps—they open and suck in small creatures in a split second.
This ability allows plants to quickly defend themselves against potential herbivorous predators. A leaf that suddenly closes can surprise an insect or an animal that wants to chew it, thereby limiting damage. This mechanism also prevents the plant from losing too much water during hot or windy periods by closing just a few leaves instead of the entire structure. It is also useful for avoiding injury during severe weather or protecting the delicate parts of the leaves from heavy rain. In short, it is a kind of survival insurance in harsh environments.
Studying these sensitive plants allows researchers to better understand how plants perceive their environment. This knowledge can then inspire innovations in robotics, particularly by creating robots capable of intelligently interacting with their surroundings through sensors inspired by these plants. It also generates ideas in the field of smart materials, which can quickly change shape or properties in response to specific stimuli. Furthermore, a precise understanding of these plant mechanisms opens promising avenues in sustainable agriculture, by developing species that can perform better on stressed soil or respond effectively to pests. In short, these amusing plants that close up still have a lot to teach us.
Researchers are currently working on using the reactive mechanisms of plants to develop bio-inspired materials that can fold or change shape in response to their environment.
Some carnivorous plants, like the Venus flytrap, count the number of touches before closing their traps to ensure that the energy expended is worth the effort!
The rapid closing movement in some plants is caused by the rapid movement of water out of the cells, resulting in a change in internal pressure known as turgor pressure.
Charles Darwin was one of the first to scientifically study the movements of sensitive plants and to suggest that these rapid reactions were useful adaptations for their survival.
Yes, plants like Mimosa pudica or the Venus flytrap (carnivorous plant) can be grown at home. However, they require a warm, humid environment and special attention to their water and light needs.
Generally, a responsive plant like Mimosa pudica will take between 10 and 30 minutes to completely reopen its leaves. This duration varies depending on the intensity of the stimulus and environmental conditions.
No, some plants can also react to other stimuli such as light, temperature, or even the presence of certain insects. For example, sunflowers follow the path of the sun thanks to a phenomenon called heliotropism.
When a reactive leaf is touched, electrical signals propagate through the cells. In response, the cells located at the base of the leaves or leaflets quickly expel water, resulting in a sudden loss of internal pressure and thereby causing closure.
Frequently touching a plant like Mimosa pudica can indeed stress it and waste its energy. Each closure consumes energy resources, which can ultimately weaken the plant if it is constantly disturbed.
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