Auxin is a plant hormone derived from the amino acid tryptophan. An auxin may be one of several molecules, but all auxin molecules are involved in some type of cellular regulation.
Auxin molecules are one of the five major types of plant hormones. Other major groups are gibberellin, cytokinin, ethylene, and abscisic acid. Auxin was the first of these groups to be identified and chemically distinct in the 1930s.
The most widespread auxin is indoleacetic acid, or simply IAA. IAA is an auxin that is very important in the growth and development of plant tissue. In studying auxin molecules, scientists have been able to recreate similar structures called synthetic structure regulators. These “fake” auxins also encourage plant growth and have been used in many agricultural and commercial applications.
The auxin group of hormones has a wide range of uses in a plant. Auxin molecules are found in all tissues in a plant. However, they are concentrated in development centers, which are at the forefront of development. These centers release auxin molecules, which are then distributed towards the roots. In this way, the plant can coordinate its size and the growth and development of different tissues based on the gradient of auxin concentration.
Auxin affects many different cellular processes. At the molecular level, auxin molecules can affect cytoplasmic streaming, the movement of fluids within a cell, and even the activity of various enzymes. It gives direct control of auxin on plant growth, development, and proliferation of individual cells. The Auxin gradient directly affects processes such as flower initiation, fruit development, and even tuber and bulb making. Even daily, auxin levels affect processes such as phototropism, which allow the plant to follow the sun and receive the most energy. Auxin regulates this process by concentrating the plant away from the sun. This causes changes in cells, which tilts the plant towards light.
Another important feature that auxin gradients confer to many plants is a fundamental dominance. Apical dominance is formed when a single trait is growing faster and more efficiently. Eventually, the auxin released from this meristem prevents any new shoots from closing at the bottom. If the stem is cut off, many new sprouts will burst under the stem, as the auxin gradient is disrupted and the system will have to form a new leading shoot. The auxin gradient, when established, determines how fast the internode grows, which determines plant height. When discussing the function of auxin molecules in a plant, it is almost easy to discuss things they do not control.
Some scientists have also discussed the plant-like polar-auxin transport system, which is based on a nervous system. The way auxin molecules move from cell to cell is very similar to sending nerve signals to an animal’s body. The auxin molecule affects various tissues and is usually converted into another auxin. A “return signal” can then be generated. In this way, a plant may have a strong nervous system to respond to external stimuli, using many different versions of auxin and other plant hormones.
The native auxin molecules are usually derived from the amino acid tryptophan. This amino acid consists of a six-sided carbon ring, which is attached to a 5-side ring containing carbon. In this 5-sided ring, a group is connected. The only difference between most auxin molecules and tryptophan is that associated with this ring.
To make this molecule, two enzymes are required to act on tryptophan. First, an amino-transferase removes nitrogen and hydrogen from the side-chain attached to a 5-side ring. Then, a decarboxylase enzyme removes the carboxyl group, leaving only SiOH. A chloride ion attaches to a six-sided ring, and an IAA is produced. Most auxins are some derivative of this molecule.
Synthetic Auxin Analogs
After studying the structure of natural auxin molecules, the scientist was able to easily produce molecules that were similar to natural auxin. These synthetic auxin analogs have many applications. They can be used to stimulate growth in some plants. To induce routine processes, synthetic auxin treatments are used on many plant cuttings. In this way, scientists can make plant clones by cutting the plants and growing the cut in whole plants.
1-Naphthaleneacetic acid (NAA) is an incoming chemical and synthetic auxin. This fake auxin is marketed to regular gardeners. While there are some safety and handling concerns, simulated auxin molecules have been used since the 1940s to stimulate the development of cuttings. Scientists also found that auxin molecules may also have anti-growth properties.
Synthetic auxin 2,4-D (2,4-Dichlorophenoxyacetic acid), is a common weed destroyer. The auxin-like molecule affects only wide-ranging weed species. This means that it can be planted around lawns, grasslands, and other landscape plants without affecting it. However, in wide plants, it causes rapid growth in all the wrong places. Plants die quickly. There are many other synthetic auxin compounds, which have a wide variety of marketing uses.
Auxin Definition, function, Structure and Synthetic Auxin Analogs