Auxin (plant)

An auxin is an hormone plant derived from the amino acid tryptophan. An auxin can be one of many molecules, but all auxin molecules are involved in some form of cell regulation. Auxin molecules are one of the five main types of auxins. plant hormones. The other main groups are gibberellins, cytokinins, ethylene and abscisic acid. Auxin was the first of these groups to be identified and was chemically isolated in the 1930s.

The most widespread auxin is indolacetic acidor simply IAA. IAA is an auxin that is very important in the growth and development of plant tissues. By studying auxin molecules, scientists have been able to recreate similar structures, called synthetic growth regulators. These “fake” auxins also stimulate plant growth and have been used in many agricultural and commercial applications.

Function of auxins

The auxin group of hormones has a wide range of uses in a wide range of applications. plant. Auxin molecules are found in all tissues of a plant. However, they tend to concentrate in the meristemsgrowth centres that are at the forefront of growth. These centres release auxin molecules, which are then distributed to the roots. In this way, the plant can coordinate its size and the growth and development of different tissues in function of the concentration gradient of auxins.

Auxin affects many different cellular processes. On a molecular level, auxin molecules can affect the cytoplasmic fluxthe movement of fluids within a cytoplasmic cell and even the activity of various enzymes. This gives auxin direct control over the growth, development and proliferation of individual cells within the plant. The auxin gradient directly affects processes such as flower initiation, fruit development and even tuber and bulb formation. Even on a daily basis, auxin levels affect processes such as the phototropism.This allows the plant to follow the sun and get the most energy. Auxin controls this process by concentrating on the side of the plant away from the sun. This causes changes in the cells, which bias the plant towards the light. This can be seen in the picture below.

Another important feature that auxin gradients provide for many plants is. apical dominance. Apical dominance is formed when a single meristem grows faster and more efficiently. Eventually, the auxin released from this meristem inhibits new shoots from sprouting below it. If the stem is cut, many new shoots will emerge below the stem, as the auxin gradient has been interrupted and the system must create a new main shoot. The auxin gradient, when established, determines how fast the new shoots grow. internodeswhich determines the height of the plant. When discussing the function of auxin molecules in a plant, it is almost easier to discuss the things they do not control.

Some scientists have even looked at the polar auxin transport system as a plant version of the nervous system. The way auxin molecules move from one cell to another is very similar to how a nerve signal is sent through an animal’s body. The molecule auxin molecule affects several tissues and is usually converted into another auxin. A “feedback signal” can then be generated. In this way, using the many different versions of auxin and the other plant hormones, a plant could feasibly have a robust nervous system to respond to external stimuli.

Structure of auxin

Native auxin molecules are normally derived from the amino acid tryptophan. This amino acid has a carbon ring six-sided, attached to a five-sided carbon-containing ring. This 5-sided ring has an attached group. The only difference between most auxin molecules and tryptophan is what is attached to this ring. The common auxin IAA can be seen below.

To create this molecule, two enzymes are needed to act on tryptophan. First, a aminotransferase removes a nitrogen and a hydrogen from the side chain attached to the 5-sided ring. Then, an enzyme decarboxylase removes the carboxyl groupleaving only COOH. A chloride ion attaches to the six-sided ring and IAA is born. Most auxins are a derivative of this molecule.

Synthetic auxin analogues

After studying the structure of natural auxin molecules, scientists were able to easily produce molecules similar to natural auxins. These synthetic auxin analogues have many applications. They can be used to stimulate the growth of certain plants. Treatment with synthetic auxins is used in many plant cuttings to induce rooting processes. In this way, the scientist can make clones of plants by taking cuttings and growing the cuttings into whole plants.

1-naphthaleneacetic acid (NAA) is a rooting chemical and a synthetic auxin. This fake auxin is marketed to regular gardeners. While there are some safety and handling issues, fake auxin molecules have been used since the 1940s to stimulate the growth of cuttings. The scientist also discovered that auxin molecules could also have anti-growth properties.

The synthetic auxin 2,4-D (2,4-dichlorophenoxyacetic acid) is a common herbicide. The auxin-like molecule affects only the weed species of leaf wide. This means that it can be applied around lawns, grasses and other garden plants without affecting them. However, on broad-leaved plants it causes rapid growth in all the wrong places. Plants die quickly. There are many other synthetic auxin compounds, which have a variety of marketed uses.