It is plant, it is painful

2010/11/01 Roa Zubia, Guillermo - Elhuyar Zientzia Iturria: Elhuyar aldizkaria

• Biologia
• Botanika
• Anatomia/Fisiologia

Someone said plants have no brain because they don't want to get bored. It was a joke, but apart from the joke, it is an interesting phrase; in order to get bored they would need a nervous system, including the brain, and plants do not have nervous system. However, some plants act as if they have nervous system.

One of the most surprising is a mimosa. Mimosa pudica is the scientific name, Latin pudica means shy. The plant has similar names in several languages. Sensitive and sleepy in Spanish, honteuse in French, schamhaft in German and many other words appear in the common names of the plant, and in all cases means sensitive or shy. The name in Basque is also representative: minbera.

These names are because the plant wraps leaves when in contact with the wind or other things or when it is hot. Perceive physical contact: touch.

It is not like the animal, it is not a sense of the nervous system. But the answer is very fast; in less than a second it collects the leaves. It also has the ability to bend a branch that holds the leaves. Apparently he is shy of physical contact.

Of course, it has nothing to do with emotions, it is a defense mechanism to protect yourself from herbivores, among others. With the leaves and twigs wrapped, the plant adopts a withered form. In addition, leaf collection is a good defense against other dangers; heat, change of brightness and the wind itself can also cause the "shrinkage" of the leaves.

Given the speed of this response, scientists postulated that it had a muscular and nervous system. But it is a plant that does not have.

Pumping water

The ability to move quickly should be sought in special cells. Plant cells are rigid, as they are full of water, as the air is in an inflated tire. The membrane collects the leaves extracting water from cells located in a strategic place.

These cells are found in the leaf tap, in a small esplanade. And by removing water from the lower cells of this esplanade – not from the upper ones – the leaf falls. Folding. Very quickly, the membranes of these cells become very porous, the water comes out and the cells lose stiffness. The structure that holds the blade suddenly does not hold it and it is rolled up.

The mechanism of instant porosity is not fully studied. These cells contain aquaporins in the membrane, that is, the water channels, like all the cells that must evacuate water quickly (for example, our kidney cells). And it is clear that the process involves concentrations of some ions, especially calcium. But the concrete mechanism is not known.

However, it is known that the functioning of the traps of some carnivorous plants is similar. Dionea (plant of the genus Dionaea) has a toothed leaf in the form of a mouth and when an insect remains on it, the plant closes the leaf and catches the insect. This movement is rapid and occurs by removing water from some cells, as in the case of the tongue.

However, the movement of these leaves in the mouth of Dionea is very limited. They can rarely make movement throughout life. The mechanism is not permanent opening and closing. It is clear that it is not a movement of a muscle.

No neurons

The greatest doubt has been about the nervous system of pain and Dionea. In the case of pain, the stimulus travels from one side to the other of the plant. Sometimes the membrane flexes the branches as in a chain reaction. Once the affected branch is collected, one is collected next to it, and then another, until the effect extends to the entire plant. In the case of the Dionea carnivorous plant, there are sensitive hairs that send an electrical signal to close the blade.

A substance must expand the stimulus, a hormone, but scientists have not yet identified it. However, the diffusion of this substance has nothing to do with a nervous system. Having a nervous system means at least being neurons.

Plant cells, of course, use electrical signals to communicate, for example. But neurons take a step further, their entire membrane responds to electricity and transmit the signal as if they were part of a cable. Plant cells do not.

However, not all scientists agree with it. A Neurobiological Plant Association was created by some who disagree. They argue that plants have an analogous animal nervous system. But most biologists say no, that plants have mechanisms that have the same function but do not have an alternative nervous system. Most agree with the joke: plants have no capacity to get bored.