The geotropism it’s a kind of tropism: an orientation shift or tilt performed by a sessile organism (which is fixed in the substrate) to respond to a stimulus. In this case, the tropism in question is produced by the force of gravity.
The gravity is a force exerted by the planet Land on the totality of the bodies that are on its surface. The earthly center attracts all objects with mass, which are acted upon by this force. Plants, in this framework, respond to gravity through geotropism.
Also called gravitropism, geotropism is a reaction to the intensity of the gravitational field. The roots of the plants, to be able to fulfill their functions, grow towards the interior of the Land, sinking into the substrate; the stems, on the other hand, develop their growth upwards, spreading on the surface.
The different concentrations of auxin allow the plants develop geotropism. This plant hormone or phytohormone is responsible for regulating the growth of the plant, promoting cell development. Depending on how the auxin is concentrated, the specimen grows in one way or another.
When geotropism accompanies the force of gravity, there is talk of positive geotropism (the roots). On the other hand, if geotropism is the opposite of gravity, it is a negative geotropism (the stems).
Geotropism, in short, allows plants to develop, subsist and reproduce. With negative geotropism, the stems and leaves develop in the aerial environment and can carry out the photosynthesis thanks to sunlight; With positive geotropism, the roots move in the same direction as gravity to access the nutrients and water they need.
Returning to the concept of auxin, we can say that it is a set of phytohormones, which are also known as hormones vegetables, and are the substances that plant cells produce. They are generally found in leaves and their action on other types of cells is equivalent to that of a chemical messenger.
The main role of auxin in the regulation of the developing It is the elongation of the plant cells. The synthesis of these hormones takes place in the stem apical meristem, a meristematic tissue (that is, it is responsible for growth) that is located at the tip of the plant, in particular in the area of division and expansion of cells, and gives rise to the stems, leaves and flowers.
Precisely, at the core of the definition of geotropism is this group of plant hormones, which reaches its maximum level in the apex and it descends as it moves away from it.
In the geotropism of hypocotyls (the germinating part of the seed) of soybeans, it has been found that some Messenger RNA small (the ribonucleic acid that carries the genetic code from the DNA of the cell nucleus to some ribosome located in the cytoplasm), which are known by the name SAURs. The synthesis of SAURs requires the addition of auxins for their stimulation.
The expression of SAURs in soybean sprouts growing in a vertical direction is symmetrical, while for those with horizontal growth the expression is modulated so that they accumulate especially in the basal half of the hypocotyl. In this way, the response that gives rise to the curvature of the organ and the increase in verticality of the plant begins. This is just one example of geotropism that demonstrates the complexity of the processes that take place in living things, no matter how small.