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Gibberellins

They are preset in all plants and can also be found in fungi, bacteria and algae. Its content can vary depending on the phenological status of the plant and can be found mainly in the reproductive tissues, but also in stems, roots, leaves, flowers, fruits and seeds.

The biosynthesis of gibberellin starts at the beginning stages of terpenoid compound synthesis route, up to synthesis of geranyl-geranyl pyrophosphate, the precursor of diterpenes which by cyclization produce the ent-kaurene molecule from which all gibberellins are derived. The synthesis takes place within the plant’s stems apices and roots, expanding leaves, fruits, as well as in developing seeds. Gibberellins can travel through the plant mainly through the phloem, but unlike auxins, they lack polar transport.

The mode action of gibberellins depends on their binding to transport proteins, first by allowing their inclusion into the cell, and subsequently by binding to a specific receptor, thus entering into the cell’s nucleus and altering the synthesis of the genetic material (RNA).

Gibberellins are mainly involved in stem growth stimulation by activating cell division and modifying the cell wall’s expandability. They also play an important role in controlling flowering induction, growth and production and fruit maturation, as well as the development and maturation of the fruits, and the germination of the seeds. As an example, we have the action of gibberellins during the germination process. In the seed, gibberellins act on the expression of the genes for α-amylase, an enzyme responsible for the hydrolysis of starch to produce simple sugars that will be the source of energy for the seedling during germination, until it can perform its own photosynthesis. Likewise, the gibberellins produced in the seeds regulate the fruit’s growth, in fact in some plant species it has been seen that in non-pollinated fruits, the application of gibberellins substitutes the effect of pollination, developing the fruit.

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