SISMONASTIA: CHARACTERISTICS, MECHANISM OF ACTION AND EXAMPLES - BIOLOGY - 2024

The sismonastia, also called sismonastismo is a nastia or involuntary movement caused by a mechanical action as a blow or jolt. It is the movement that is perceived in the roost (mimosa pudica), which closes its leaves immediately after being touched.

In this way, the friction or touch spreads through the plant generating the closure of several leaflets. In fact, the plant perceives movement as a threat, since sismonastia is considered a defense mechanism.

Sismonastia in Mimosa pudica. Source: pixabay.com

Nastias are transitory movements in a plant in response to an external and precise stimulus. They are based on growth mechanisms or turgor changes of groups of cells that expand their water content.

The petiole of the leaves of some mimosas of the Fabaceae family has a thickened base called the pulvínulo. By variation of turgescence, this structure allows the movement of the leaves induced by external agents; in this case, a shake.

The species Dionaea muscipula (Venus flytrap) closes its mucilaginous leaves upon contact with an insect, which it uses for its nutrition. In other species, sismonastia occurs in flowers, caused by anther movements and favoring pollination.

Mechanism of action

Of the nystatic plants, the mimosa pudica is a typical example of this phenomenon produced by rapid seismonastic movements, specifically those caused by mechanical, electrical, chemical stimuli, variations in temperature, injuries or strong light intensity.

This event can occur due to natural events such as strong winds, raindrops or the intervention of insects and animals. The movement is a quick response, within 1 to 2 seconds, and returns to the starting position after 8 to 15 minutes.

Electric conductivity

The mechanism of action occurs due to the electrical conductivity that transmits the stimulus to the pulvulus, at the base of the petiole. The loss of turgor of the abaxial motor cells of the pulvulus causes a change in the disposition of the petiole.

After a few minutes, the cells regain their initial turgor and the petioles return to their original arrangement. In the case of very strong stimuli, the wave is emitted throughout the plant, which causes the total closure of the leaflets.

In some situations where the stimulus occurs continuously, the plant adapts and keeps the leaflets extended. Through this adaptation mechanism, the plant avoids the closure of the leaflets caused by wind or rain.

Chemical signal

The explanation of the mechanism of reception and radiation of the stimulus is carried out by means of a chemical signal. Substances called turgoporins - glycosylated derivatives of gallic acid, isolated from Mimosa sp species - act as a neurotransmitter.

In the same way, the concentration of calcium and potassium ions promote the exit of water from the cells. A higher concentration of ions causes the transfer of water to intercellular spaces, causing the leaflets to close or contract.

Examples

Mimosa (m

The mimosa pudica is a shrubby plant belonging to the Fabaceae family, native to the American tropics. It is characterized by seismonastic movements caused by reaction to touch as a defense mechanism against predators.

This plant has different names. The most common are sensitive mimosa, nometoques, moriviví, dormilona, ​​dormidera or poppy. It has bipinnate compound leaves, consisting of between 15 and 25 pairs of pinnae in a linear position and an obtuse angle.

Mimosa (Mimosa pudica) Source: pixabay.com

The small pinkish-hued flowers have a pedicelled head between 2 and 3 cm in diameter. It is a perennial taproot plant with numerous secondary roots, and a foliar area that reaches 80 or 100 cm in height.

The movements of the leaves composed of various leaflets are particular, which retract and close at the slightest blow. In fact, the smaller stems fold under the weight of the leaflets as a mechanism generated at the base of the pedicel.

Upon retreating, the plant reveals a weak and withered appearance as a defense mechanism against attack by predators. Likewise, it is a moisture retention mechanism on hot days or protection from strong winds.

Osmosis

This process is stimulated by osmosis. The presence of K ⁺ ions causes cells to lose water by osmotic pressure, causing turgor. The leaflets open or close according to the flexor or extensor cells where said turgor occurs.

In contrast, mimosa leaflets remain folded during the night hours, a phenomenon known as nictinastia. This is an example of the physiological processes of the plant, regulated by the incidence of solar radiation.

Dionaea muscipula

The Venus flytrap is a carnivorous plant of the Droseraceae family capable of trapping live insects with its leaves. Its very short stems - barely between 4 and 8 cm long - support the longer and more robust leaves that form a trap.

Each plant has a colony of between 4 and 8 leaves that develop from the underground rhizome. The specialized leaves present two differentiated regions; the petiole area is flattened and heart-shaped where the photosynthetic process occurs.

Dionaea muscipula (venus flytrap) Source: pixabay.com

The true leaf is made up of two lobes attached to a central vein, forming a kind of trap. The inner surface of each lobe contains three trichomes with anthocyanin pigments and hairs or cilia on the edges.

The closure mechanism is activated when the prey makes contact with the sensory trichomes located in the bundle of each lobe. In addition, each lobe features scalloped edges by interlocking cilia-like structures that prevent prey from escaping.

How active?

The explanation of the mechanism by which the trap closes rapidly includes a continuous interaction of turgor and elasticity.

The plant perceives the prey through the sensory trichomes located on the inner surface of the leaves. At the first contact, a variation in the electrical potential of the cells is created, similar to the reactions that occur in neurons; in this way the seismonastic movement is activated, but it is only closed if the insect remains in motion.

The double contact of the prey on the sensory fibers is a safety system that prevents the expenditure of energy; in this way the plant guarantees that the prey is alive and provides it with food.

References

1. Diaz Pedroche Elena (2015) The Plant Relationship Process. Department of Biology-Geology. 12 p.
2. Dionaea muscipula (2019). Wikipedia, The Free Encyclopedia. Recovered at: wikipedia.org
3. Mimosa pudica (2018) Wikipedia, The Free Encyclopedia. Recovered at: wikipedia.org
4. Sismonastia (2016) Wikipédia, a encyclopedia livre. Recovered at: wikipedia.org
5. Sotelo, Ailin A. (2015) The Movement of Plants: Tropism and Nastias. Plant Physiology- FaCENA -UNNE. 11 p.