It is a temporary movement of certain organs of a plant in the face of an external and diffuse stimulus. It is based on the phases of growth or changes in turgor of various cell groups that change their volume by controlling the entry and exit of water.
They are active and reversible movements, they are not directed towards the stimulus so they do not act in the direction in which the plant should react. It largely affects flat organs such as petals, tender leaves and longitudinal growth organs such as branches, tendrils, among others. They are classified in:
- Photonasty: In response to light, flowers open or close their petals at dawn or dusk.
- Geonasty: It is derived by gravity and the physiological dorsiventrality of the plant organ.
- Haptonastia or tigmonastia: It is the response to contact, it occurs in the tendrils of many plants. A growth of the flank opposite to the contact is generated.
- Hydronasty: It is the response to the humidity of the environment.
- Chemonasty: It is the response to chemical agents.
- Nyctinasty: The position of the leaves changes with the day and night.
- Seismonastia: It is the response generated by a blow or shake on the plant. An example is the movement of carnivorous plants or different mimosas.
- Thermonasty: It is the response to changes in temperature.
- Traumatonastia: It is generated by a wound or as a consequence of it.
It is the movement used by plants or their organs to respond to an external stimulus. The tropism can be positive, when it accompanies the stimulus and negative, when the reaction is contrary to the stimulus. There are different types of tropisms depending on the nature of the stimulus:
- Gravitropism: It is in charge of taking the roots to the ground and that the stems unfold upwards until they come to the surface.
- Phototropism: Plants react to light, going to the area with the best lighting.
- Heliotropism: Involves the movement of the plant depending on the orientation of the sun.
- Chemotropism: It is the response to the chemical elements that a plant needs or that harm it.
- Thermotropism: They lead plants to move to a fixed temperature.
Difference Between Nasty and Tropism
- A tropism is the response of a plant or animal to a stimulus that orients them with a high intensity towards the stimulus or to flee from it.
- Nastias are rapid and reversible movements of a plant in response to an external stimulus. But they are not influenced by the direction of the stimulus.