Geotropism is a tropism produced by the force of gravity.
Geotropism is a type of tropism : a displacement or inclination of orientation made by a sessile organism (which is fixed on the substrate) to respond to a stimulus. In this case, the tropism in question is produced by the force of gravity.
Gravity is a force that planet Earth exerts on all the bodies that are on its surface. The Earth's center attracts all objects with mass, which receive the action of this force. Plants, in this framework, respond to gravity through geotropism.
What is geotropism
Also called gravitropism , geotropism is a reaction to the intensity of the gravitational field . The roots of plants, in order to fulfill their functions, grow towards the interior of the Earth , sinking into the substrate; The stems, on the other hand, develop their growth upwards, extending over the surface.
Different concentrations of auxin allow plants to develop geotropism. This plant hormone or phytohormone is responsible for regulating plant growth, promoting cell development. Depending on how the auxin is concentrated, the specimen grows in one way or another.
The downward growth of the roots shows positive geotropism.
Classification according to type
When geotropism accompanies the force of gravity , we speak of positive geotropism (the roots). On the other hand, if geotropism is opposite to gravity, it is a negative geotropism (the stems).
Geotropism, in short, allows plants to develop, survive and reproduce. With negative geotropism, the stems and leaves develop in the aerial environment and can carry out photosynthesis thanks to sunlight; With positive geotropism, roots move in the same direction as gravity to access the nutrients and water they need.
Geotropism and auxin
Returning to the concept of auxin , we can say that it is a set of phytohormones , which are also known as plant hormones , and are the substances produced by plant cells. They are usually found in leaves and their action on other types of cells is equivalent to that of a chemical messenger.
The main function of auxin in the regulation of development is the elongation of plant cells. The synthesis of these hormones takes place in the apical meristem of the stem , a meristematic tissue (that is, responsible for growth) that is located at the tip of the plant, particularly in the area of cell division and expansion, and It gives rise to stems, leaves and flowers.
Precisely, at the core of the definition of geotropism is this group of plant hormones, which reaches its maximum level at the apex and decreases as it moves away from it.
The SAURs
In the geotropism of the hypocotyls (the germinating part of the seed ) of soybean, it has been proven that small messenger RNAs are involved (the ribonucleic acid that carries the genetic code from the DNA of the nucleus of the cell to a ribosome located in the cytoplasm), which are known as SAURs . The synthesis of SAURs requires the addition of auxins for stimulation.
The expression of SAURs in soybean sprouts that grow vertically is symmetrical , while for those that grow horizontally the expression is modulated so that they accumulate especially in the basal half of the hypocotyl. In this way, the response begins that gives rise to the curvature of the organ and the increase in verticality of the plant. This is just one example of geotropism that demonstrates the complexity of the processes that take place in living beings, no matter how small they may be.