Plant hormones: what are they and what are their functions?

Pflanzenhormone: Welche gibt es und was sind ihre Funktionen? - FARBIO® - Nachhaltige Bio-Flüssigdünger aus Hamburg

The hormones in plants are also called phytohormones. They are plant-specific chemical compounds that control important processes within the plant. Phytohormones are messenger substances that transmit important information and growth regulators. Many different hormones interact, which is why it is not only relevant whether a hormone is present, but also in what concentration.

What are gibberellins?

The gibberellins are the hormones of a plant that are responsible for the germination of seeds and buds. They also encourage flowering in a plant. Gibberellins give plants the impetus for shoot elongation, especially in young plants. They are mainly formed in growing parts of plants. The hormone is involved in the process that makes a plant grow towards the sun.

And auxins?

Auxins, other phytohormones, migrate to the shady side of the shoot axis, where the gibberellins are activated there and ensure growth in length. This is how the plant bends towards the sun.

Auxins are among the first discovered hormones in plants. They are synthesized in the shoot tip, which is why plants can no longer continue to grow without them. Because auxins are also involved in the growth of a plant by promoting the expansion of cells and thus the growth in length of the shoot axis and roots. The growth of flowers and fruits is also influenced by the presence of auxins. 

How are cytokinins related to auxins?

Cytokinins are the hormones in a plant that ensure the balance between roots and shoots. In this context, cytokinins work in tandem with auxins because by balancing the levels of the two, a plant can determine whether it needs to develop more roots or shoots. Since cytokinins are formed in the roots, an excess gives the plant the signal to develop more shoots. If more auxins are present, which are formed in the shoot tips, root growth is stimulated. The phytohormone particularly promotes the growth of the lateral shoots of a plant. Cytokinins also ensure that the aging process of a plant is slowed down.

What is the role of ethylene?

Ethylene is not only active within a plant, but also serves as a messenger between plants. It is produced from the amino acid methionine within the plant. Fruits ripen through the stimulation of ethylene, which is responsible for breaking down cell walls. This makes fruits softer and increases the sugar content. It causes the aging of leaves and flower organs and eventually promotes leaf fall. Ethylene is also important for germination and growth of sprouts. It causes the sprouts to thicken, shorten and curve.

What is abscisic acid?

The phytohormone abscisic acid is produced in the chloroplasts in response to stress, such as drought or cold. Abscisic acid helps the plant to regulate its water balance. Thus, stomata, the stomata of a leaf, are closed as soon as the plant does not get enough water. This counteracts water loss through transpiration. In response to low temperatures, the hormone ensures that buds and seeds do not germinate in winter. This is the initiation of dormancy, known as seed dormancy.

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