Why is the mimosa shy?

Why is the mimosa shy? Because plants are different from animals in that they have no nervous system and no muscles, they will not sense external stimuli, while mimosa is different from other plants. When touched by the outside world, the petiole is drooping and the small leaves are closed. This action is understood as "shy", so it is called mimosa, mimosa, and ugly grass.

Mimosa cells are supported by tiny reticular protein actin (leaf occipital sensitive constrictor). When there is a closed movement, the phosphate of actin will fall off, as long as the mimosa absorbs the compound that does not let the phosphate fall off, it will not change after touching. Professor Takeshi pointed out that when the actin bundle is dispersed, the cells are destroyed, resulting in water running out, resulting in closed movement. Actin is commonly found in animal muscle fibers and is related to muscle stretching. Unexpectedly, it also exists in mimosa, which can be said to be quite rare.

The movement of plants is usually caused by changes in intracellular turgor. Most mature plant cells have a large vacuole. When the vacuole is filled with water, it presses the surrounding cytoplasm so that it clings to the cell wall, putting pressure on the cell wall and causing the cell to swell like a balloon full of air. The concentration of organic and inorganic substances in the vacuole determines the osmotic pressure, and the osmotic pressure can determine the direction of water diffusion. When the concentration of vacuole increases, the osmotic pressure increases, water spreads from extracellular to intracellular and enters the vacuole, which increases the swelling pressure of the cell and makes the cell bulge; on the contrary, the cell shrinks. This process can only lead to slow movement, such as the opening and closing of stomata.

If the leaves of mimosa are touched, they will close immediately. The more powerful they are, the faster they close, and the whole leaves will hang down as if they are weak, and the whole action will be completed in a few seconds. The leaves and petioles of mimosa have a special structure. At the base of the petiole and at the base of the leaflet of the compound leaf, there is a relatively inflated part called the leaf pillow. The leaf pillow is the most sensitive to stimuli. As soon as it touches the leaf, the stimulus immediately spreads to the pillow at the base of the petiole, causing the two small leaves to close, with a greater kinetic force, not only to the pillow of the leaflet, but also quickly to the pillow at the base of the petiole, and the whole petiole droops. What causes it? This is because there is a large vascular bundle in the center of the leaf occipital, which is surrounded by parenchyma with many intercellular spaces. When the vibration reaches the leaf pillow, the cell fluid from the parenchyma cells in the upper half of the leaf pillow is discharged into the intercellular space, which reduces the turgor pressure of the cells in the upper part of the leaf pillow, while the parenchyma cell space in the lower part still maintains the original turgor pressure. as a result, the leaflets stand upright and the two leaflets close, even the whole leaf hangs down. It has been studied that mimosa leaves close within 0.08 seconds after being stimulated. After being stimulated, the conduction speed is also very fast, with a maximum speed of 10 centimeters per second. After the stimulation, after a short period of time, everything slowly returned to normal, the lobules spread out again, and the petiole stood up. The recovery time is usually 5-10 minutes. However, if we continue to tease and stimulate its leaves one after another, it will feel "bored" and will no longer react. This is because continuous stimulation causes the loss of cellular fluid in the leaf occipital cells and can not be replenished in time.

The special ability of mimosa has its historical roots. Its hometown is in Brazil in tropical South America, where there are often strong winds and heavy rain. Whenever the first drop of rain hits the leaf, the leaf immediately closes and the petiole droops to avoid the damage caused by the storm. This is a kind of adaptation to the change of external environmental conditions. In addition, the exercise of mimosa can also be seen as a way of self-defense. When an animal touches it, it closes its leaves, and animals dare not eat it any more.

There is a larger part at the base of both the petiole and the petiolule, called the leaf mattress. The leaf mattress is very sensitive to stimuli, and there are many parenchyma cells in its center. When at rest, these cells transport negatively charged chloride ions into the cells and oxygen ions outside the cells, maintaining a certain potential difference between the cell membrane and the surrounding area, called the resting potential. When the external stimulation exceeds a certain limit, the permeability of this difference will suddenly change, and a large number of positively charged calcium ions will pour into the cell, while potassium ions will proceed in the opposite direction, increasing the potential in the membrane, or even becoming a positive potential, resulting in an action potential, a phenomenon called depolarization. The action potential will be transmitted, and when the cell reaches the action potential, that is, when the depolarization occurs, the differential permeability of the cell membrane will disappear, so that the water originally stored in the vacuole will be discharged in an instant, causing the cell to lose turgor and become paralyzed. Therefore, when stimulating the leaf mattress at the base of the petiolule, the swelling and pressure of the parenchyma cells in the upper half of the leaf mattress decreased, while the parenchyma cells in the lower half remained the original pressure, causing the leaflets to stand upright along the petiole direction. On the other hand, the vascular bundle in the petiole synthesizes a large pipe in the leaf mattress to hold the water discharged from the leaf mattress.

The research team led by the reason for the "shyness" of mimosa has solved the mystery of the closed movement of mimosa: mimosa cells are supported by tiny, reticulate protein "femoral eggs" (leaf pillow sensitive contraction). When there is a closed movement, the phosphoric acid of actin will fall off, as long as the phosphate does not fall off, it will not change after touching. Professor Takeshi pointed out that when the thigh actin bundle is dispersed, the cells are destroyed, resulting in water running out, resulting in closed movement. Actin is commonly found in the muscle fibers of animals and is related to muscle stretching. Unexpectedly, it also exists in mimosa, which can be said to be quite rare.