WHAT IS PHOTONASTIA? - BIOLOGY - 2024

The fotonastia is the time response of a plant to a light stimulus. Plants are living beings capable of reacting to the presence of external stimuli. In the case of photonastia, these stimuli come only from external contact with a light source.

According to botany, the nastia is defined as the temporary movement of a plant, where certain organs of the plant react to the presence of an external agent. It is said that it is a temporary movement, since the plant recovers its state once it loses contact with the external stimulus.

In the specific case of photonastia, there are two different groups of plants that react before light stimuli. Some react during dawn or in the middle of the day, and others only react with late afternoon or early night.

Those plants whose life cycle depends on photonastia tend to alter their biological clock by being placed in a dark place.

This is because plants have their cycle regulated according to the amount of light hours they receive. When they stop receiving these hours of light, they change the frequency with which they open and close their petals.

Characteristics of photonastia

Photonastia is a type of nastia that occurs in certain plants against changes in light. This phenomenon can occur both during the day and at night, depending on the type of plant that responds to the stimulus.

Some flowers close their petals when sunlight falls and keep them open during the day.

Photonastia is similar to the phenomenon of phototropism, since the flat organs of certain plants respond to light stimuli.

However, photonastia appears as a temporary or temporary reaction, while phototropism is a permanent state change, once the stimulus is applied.

The changes produced by photonastia are reversible and temporary. Its strength varies according to the intensity of the light stimulus applied.

In some cases the presence of light produces the opening of the plants and the lack of said stimulus produces their closure. However, this phenomenon can occur in the opposite way. In this way, you can see how some flowers that must open during the day, remain closed when the sky is gray or cloudy.

Also, if one of these plants were put inside a dark room, its biological clock would be greatly affected and the opening and closing cycle of its petals would gradually change as the days go by.

In the following video you can see the photonstic movement of a flower:

What is the nastia?

The nastia is a movement that lacks direction and takes place temporarily. It happens when an external and imprecise stimulus is applied to certain plant organs of some types of plants.

Nastia takes place in plants depending on their growth stage and the change in the meatiness of the cells that make them up.

Meatiness is the variation in the volume of water that enters and leaves each cell of a plant, and that is not influenced by the presence of any external stimulus.

Another way of defining nastia is as the succession of movements that take place in an active and reversible way, produced by the application of a non-focused external stimulus.

This means that the stimuli are not produced with the intention of generating a reaction on the plant, therefore, they can come from any direction.

The nastia mainly affects the flat organs of the plants, such as the young leaves, the petals and some organs that influence the longitudinal growth of the plant.

These longitudinal organs include the leaves, joints, branches, and tendrils, among others. They are characterized because they can only be bent in one direction.

There are different types of nastias, each of them is classified according to the type of stimulus and reaction that is generated. On the other hand, the variation in the intensity of the stimulus will also affect the type of nastic response.

Difference between photonastia and phototropism

Nastias and tropisms are movement phenomena that take place in plants in the presence of an external stimulus. However, these two phenomena differ from each other mainly by the duration of the movement after the stimulus is applied.

In the case of tropisms, the response of the plant to the stimulus is irreversible and permanent. On the other hand, in the case of nastias, the movement takes place each time the stimulus is presented, this response being completely reversible.

In this way, photonastia can be differentiated from phototropism, both phenomena being related to the presence of an external light stimulus.

Photonastia responses can last a few hours or minutes, while phototropism responses are permanent.

On the other hand, the movements produced by photonastia do not have a definite direction, while the movements of phototropism have a definite direction.

An example of phototropism can be the growth of a flower stem, which requires the incidence of sunlight to fully develop, but once it occurs, it cannot be undone.

Another difference between these two phenomena is the speed with which they happen. Tropisms are usually slow, while nastias can occur in seconds.

Examples of photonastia

Sunflower

The sunflower is a good example of photonastia, as the orientation of the flower will change depending on where the light comes from. This type of flower will always seek to position itself in such a way that it can receive greater exposure to sunlight.

For this reason, the sunflower is said to sleep at night, as it drops its petals downward in the absence of sunlight. When the flower opens or moves during the day, it speaks of a positive photonastia.

Dondiego at night

Contrary to the sunflower, the morning glory presents a negative photonastia, since its movement takes place in the absence of sunlight.

In this way, the flower will open its petals once dusk arrives or night falls.

References

1. (2017). BioDic. Obtained from Fotonastia: biodic.net.
2. Chuletas, P. (October 26, 2011). Xuletas. Obtained from Phototropism and nastias of plants: xuletas.es.
3. Miguel, J. (June 7, 2017). com. Obtained from Description of tropisms and nastias with examples: elblogverde.com.
4. NOTARY, J. (June 27, 2013). A site for science. Obtained from TROPISMO Y NASTÍA: unsitioparalasciencias.overblog.com.
5. SINGH, K. (2012). com. Obtained from Different types of nastic movements Movement (Plants): preservearticles.com.