Functions of Auxin

Auxin is an essential element in plant growth and development, instigating cell division, elongation, and segmentation.

Discovery of Auxin

A Dutch graduate student named Frits Went first described auxins in 1926 and chose the name auxin from the Greek word ‘auxien,’ which means ‘to grow.’ Went isolated the plant hormone auxin as indole-3-acetic acid (IAA). Subsequently, during the first half of the 20th century, four other phyto-hormones, including cytokinins, abscisic acid, ethylene, and gibberellins, were discovered. Auxin functions regulate various aspects related to plant development, such as cell division, differentiation, embryonic development, elongation, apical dominance, stem and root tropism, and flower formation.

Structure of Auxin

Native auxin molecules are obtained from the amino acid tryptophan.

This particular amino acid has a carbon ring which is six-sided and attached to a five-sided carbon ring.

A group is attached to this 5-sided ring.

Two enzymes that act on tryptophan are required to create this molecule.

First, an amino-transferase removes nitrogen and hydrogen from the 5-sided ring’s side chain.

The carboxyl group is then removed by a decarboxylase enzyme, leaving only COOH. IAA is formed when a chloride ion attaches to the six-sided ring.

The majority of auxins are derived from this molecule in some way.

Function of Auxin

ß-indoleacetic acid is formed from amino acid tryptophan or from the breakdown of carbohydrates, which are called glycosides.

This hormone is known to affect plants by acting on the chemical bonds of the carbohydrates that make up plant cell walls. The process causes irreversible changes in the cells and is accompanied by the entry of water and the synthesis of new cell wall material.

In addition to promoting normal plant length growth, IAA and other auxins influence stem growth toward the light (phototropism) and against gravity (geotropism).

The phototropic response occurs because more auxin is distributed away from the light than toward it, causing the shaded side to elongate more strongly and thus curve the stem toward the light.

Similarly, the geotropic response occurs when more auxin accumulates on the lower side of the growing stem than on the upper side, resulting in an upward curvature.

A greater amount of auxin in the lower halves of roots is also associated with downward growth.

Functions of Auxin in the Human Body

The investigation of the effects of auxin on mammalian cell proliferation stated that though it is a plant growth hormone, it is also found in humans.

IAA is produced in the human body due to a metabolic process. It is produced by the breakdown of serotonin, primarily in the liver, and is excreted in the urine.

Serotonin is a neurotransmitter synthesised from tryptophan in the same way that auxin is synthesised in plants.

Auxin also helps to maintain apical dominance.

Most plants have lateral buds at nodes. Buds are embryonic meristems that are kept dormant. Auxin maintains this dormancy.

The lateral buds remain dormant as long as the apical meristem produces enough auxin.

How do Auxins and Cytokinins Work Together?

Auxin and cytokinin, plant hormones, interact in a complex way to control many aspects of growth and differentiation. Auxin promotes cell elongation, but it is not sufficient on its own. Auxin’s accomplice is a group of hormones known as cytokinins. Cytokinesis is the process of cell division. Cytokinins are found in areas of actively growing tissues like roots, embryos, and fruits. Cytokinins, on the other hand, require auxin to induce cell division. The cytokinin-to-auxin ratio determines where cells develop. Shoots form when cytokinin levels rise; roots form when auxin levels rise. Cytokinins do not initiate the formation of new tissues on their own. Cytokinins also help delay ageing in plants by increasing the amount of new protein produced and decreasing the amount of old protein demolished. Cytokinins are thus sprayed in flower shops to keep leaves green and cut flowers fresh.

Analogues of Synthetic Auxins

After studying the structure of natural auxin molecules, scientists could quickly produce molecules that were similar to them.

These synthetic auxin analogues are helpful in various situations. They can be used to promote the growth of specific plants.

Many plant cuttings are treated with synthetic auxin to stimulate rooting.

Plant clones can be created by taking cuttings and growing them into entire plants.

Many other naturally produced and synthetic compounds known as auxins have growth-promoting properties, but they are not always as active as IAA. Some of these compounds resist the enzymatic destruction that is the normal fate of IAA within the plant; this property is extremely useful in research and horticulture because auxin action can be prolonged.

Auxin promotes stem elongation while inhibiting lateral bud growth (maintains apical dominance). Auxin forms in the buds, root tips and stem. Promotion of cell elongation is done by auxin, which is produced at the tip of the stem. Auxin migrates to the darker side of the plant, causing the cells there to grow larger than the corresponding cells on the lighter side. This causes the plant stem tip to curve toward the light, a plant movement known as phototropism.

Conclusion

Auxin is an essential component in the regulation of plant growth. It can aid in the extension of root and stem cells. It aids in the prevention of premature fruit, flower, and leaf fall. It is hugely beneficial in terms of apical dominance. Auxin also contributes to the plasticity of plant walls, allowing the plant to grow upwards. Plant development regulates cell proliferation as well. This action causes the cells to grow even more. Another property of auxin is the formation of rooting. Auxin, which helps initiate cell patterning, also promotes cell division and meristem maintenance.