Tropism is generally an organism's directional response to a stimulus. Photomodulation is the movement of parts of a plant, during its growth, in the direction of light stimulation. This movement, caused by the uneven growth of the plant, is mainly due to the difference in the auxin density of the plant. At the point where it is less illuminated, there is a greater amount of auxin and this results in the plant growing more there and thus the shoot tilting towards the light. When the source of light is the sun, the phenomenon is called sunbathing.
Sunflower is the property that plants have to turn to sunlight. It can be positive or negative. A positive sunrise is the movement in the direction of the sun, while a negative sunrise is the movement away from the direction of the sun.
Historical data
The habit of some plants to move in the direction of the sun was already known by the Ancient Greeks. In the 19th century, botanists discovered that plant growth processes were involved and performed increasingly clever experiments. The term sunflower was first used in 1832 by AP de Candolle, a Swiss botanist, to refer to the phenomenon in any plant.
Flower sunflower
The most typical example is the sunflower. We have all seen a field full of sunflowers facing the sun. The movement is performed by motor cells in a flexible part just below the flower. The motor cells specialize in pumping potassium ions to nearby tissues, changing their vortex pressure.
Sunflower leaves
It is the solar monitoring behavior of the leaves. Alfalfa, cotton, soybeans, beans and some wild species of the mallow family (Malvaceae) are plant species that show sun exposure. The leaves watch the sun only on clear days. They stop when the clouds block the sun.
Negative roots sunflower
Unlike shoots, the roots of the plant are characterized as "negatively sunny", ie they grow away from light stimuli.
