Tropisms are plant growth movements in response to an external stimulus.
Plant growth can be either stimulus-driven or contrary to it. When growth occurs towards the stimulus, it is called positive tropism. When it occurs in the opposite direction, it is considered as tropism negative.
Tropism is controlled by auxins, plant hormones. Auxin stimulates cell elongation, controlling the direction of growth.
Types of Tropism
The types of tropisms are determined by the nature of the stimulus. The main ones are phototropism and gravitropism.
O phototropism it is growth in response to the direction of light. The stems show positive phototropism as they grow towards the light source. While the roots show negative phototropism, growing in the opposite direction to the light source.
Phototropism. Growth towards the light source.
Positive phototropism results from the direct action of auxins on cell elongation. When a plant is exposed to a light source, the auxina migrates to the dark side of the stem. This is because the light directs the auxina to the darker side. As a result, the cells on the dark side of the stem elongate more than those on the light side, so the stem bends.
Learn more about plant hormones.
O gravitropism, also called geotropism, corresponds to gravity-driven plant growth. The stem presents negative geotropism, against the sense of gravity. At its roots, geotropism is positive.
Another type of tropism is the tigmotropism. In this case, the stimulus to growth occurs when coming into contact with an object. One example is tendrils, which curl up on physical supports.
vegetable movements
At this point, you might be asking yourself: do plants move? The answer is yes. Although the movements are not compared to those of animals, plants also move, but in a slower and less dynamic way.
Plants can have three types of movements: tropisms, tactical and nastisms.
As we have already seen, tropism is related to growth movements in response to a stimulus.
Tactism involves moving cells towards a stimulus. Like tropisms, they can be positive or negative.
Nasism corresponds to movements related to relatively rapid changes in the turgor of certain cells. Unlike tropism, nastism does not involve growth and are reversible movements.
An example of nastism occurs with the poppy plant (modest mimosa). When touched, it closes its leaves in response to an external stimulus.
