Contrary to what might appear at first glance, plants move. If we look carefully, we can see that some of its parts rotate in different directions. In fact, this type of movement is not random, as plants look for light. This phenomenon is known as phototropism.
As for its etymology , this term comes from the Greek word photo, which means light and from tropes, which means whirl.
Tropism consists of changes and movements of any living organism as a result of external stimuli. When the external stimulus is light and light affects the movement of plants, it is a matter of phototropism.
Positive and negative phototropism
When there is a focus of light over a forest area, the plants move towards this focus and thus a positive phototropism occurs. On exceptional occasions, plants avoid the focus of light, producing the phenomenon of negative phototropism.
In the case of positive phototropism, ancient botanists were already trying to understand what were the internal mechanisms that explain this phenomenon. For centuries there was no satisfactory explanation, until finally a conclusion was reached : auxin is the molecule in plant cells that activates movements towards light. Auxin are plant hormones that participate in plant growth and movement.
When there is a beam of light directed at a plant, this causes the concentration of auxin to increase on the side of the plant that is away from the light. In this way, the cell walls that accumulate a greater amount of auxin stretch and the plant bends towards the light source.
Despite the advances made, it is still unknown which are the internal mechanisms that explain the concentration of auxin. However, it has been observed that blue light is the cause of the sensitivity of plants towards light. Anyway, it is known that the distribution of auxin is associated with luminosity. Phototropism
Gravitropism is associated with gravity
Tropism is a phenomenon that affects all living beings. In addition to phototropism, there is gravitropism, which is also related to plant movements. As its name implies, all these changes occur through the effect of gravity.
Thus, gravitropism explains the extension of plant roots towards the interior of the earth.
The roots of any vegetable always tend towards the force of gravity, which is known as positive gravitropism. On the other hand, the stem develops in the opposite direction to the action of gravity and this phenomenon is called negative gravitropism. Phototropism
When plant root growth is affected by the action of water, tropism is known as hydrotropism.