What is Auxin | Auxin Functions, Regulation, & Interaction
Definition of Auxin
Auxin Definition: Auxin is a plant hormone that plays a role in many aspects of plant growth and development. It was the first plant hormone discovered, and its structure was determined in the early 1900s. It synthesized auxin in plant cells, usually near the tips of roots and shoots. It regulates growth by stimulating cells to elongate on one side of the auxin maximum (the point at which auxin activity is highest). This causes them to change directionality. Auxin also plays a role in developing other plant structures, such as leaves, flowers, and fruit. The name auxin comes from the word “activity.” Auxin functions are described below:
Auxin is a plant hormone that Adolf Fick and Carl Nageli first discovered. Auxin regulates many plant growth and development aspects, including lateral root formation and plant differentiation. It is synthesized in cells near the tip of a shoot or root, from which it is transported to other areas via plasma membrane receptors. Auxin binding to Aux/IAAs transcription factors plays a significant role in influencing gene expression. Auxin is considered essential for the proper growth and development of flowers, fruit, and secondary stems.
The auxin molecule is a small, lipophilic (fat-soluble) hormone made up of an indole ring and a carboxylic acid chain. The indole ring handles the hormones’ characteristic ability to bind to DNA, while the carboxylic acid chain handles its solubility in water.
Auxin is synthesized in the cytosol, then transported to the plasma membrane. Auxins bind to two different protein receptors at the plasma membrane: the polarity protein PIN1 and the transcriptional regulator TIR1—these proteins transport auxin through cells via vesicle carriers. Auxins also bind to a group of transcription factors known as Aux/IAAs, essential for the hormone’s ability to influence gene expression.
Auxin functions are explained below:
- Auxin is a plant growth regulator that plays several roles in plant growth and development.
- Its most important function in differentiation or cellular specialization is the ability to restrict auxin transport to a specific area. In this way, it generates many degrees of local cellular development.
- Auxins also have an essential role in the dormancy and germination of seeds and lateral root formation.
- It has been demonstrated that synthetic auxin can generate a secondary stem from a leaf and that auxin is necessary for the development of flowers and fruit.
- Auxin also regulates gene expression by binding to Aux/IAAs transcription factors. This binding activates or represses the transcription of target genes. Many of these genes encode proteins involved in plant growth and development.
Synthetic Auxin Analogs
Auxin is a naturally occurring plant hormone that plays a crucial role in many aspects of plant growth and development. Auxin regulates cell division, root growth, leaf expansion, and flowering. Because auxin is so essential to plants, scientists have been working for many years to develop synthetic Auxin analogs that can mimic the effects of natural auxins. Synthetic auxin analogs are effective plant growth substances that mimic the action of natural auxins but do not occur at natural levels in plants or are not present for very long.
In some cases, synthetic auxin analogs have proven to be more potent than the natural form of the hormone at stimulating cell division. The most commonly used Auxin analog is 2,4-Dichlorophenoxyacetic acid (2,4-D).
2,4-Dichlorophenoxyacetic acid (2,4-D) is the most widely used synthetic auxin. It is safe for humans and other mammals, but studies show that chronic exposure to 2,4-D at very high concentrations can cause rodent liver damage. Although it is often used in agriculture, 2,4-D is not registered in some countries, such as Germany.
3,6-Dichloro-2-pyridinyloxyacetic acid (3,6-D) is a synthetic auxin that effectively stimulates plant growth. Like 2,4-D, it is a chlorophenoxyacetic acid. 3,6-D has been used to promote the growth of rice, wheat, cotton, and other crops. It is also used as a herbicide.
1-Naphthaleneacetic acid (NAA) is a synthetic auxin used to promote rooting in cuttings. When used at high concentrations, NAA can cause root damage and even death.
Many other synthetic auxin analogs have been developed over the years. Some of these include:
- 3,5-Dichlorophenoxyacetic acid (3,5-D)
- 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T)
- Butyric acid
- IBA (Indole-3-butyric acid)
Benefits of Synthetic Auxin functions
The benefits of synthetic auxin functions analogs have been well documented and include:
- Increased plant growth:
Synthetic auxins promote plant growth by stimulating cell division and expansion. This results in larger, healthier plants with more vigorous root systems.
- Increased crop yields:
Many crops respond to synthetic auxin application by increasing yield. 2,4-D and other Auxin analogs have been shown effective on many crops, including peas, beans, tomatoes, and many others.
- Renovation of pasture grasses:
Synthetic auxins are used to renovate pasture grasses, such as Poa annua and Cynodon dactylon by killing the existing vegetation and encouraging grasses to grow.
- Improved crop quality:
The use of synthetic auxins can also improve the quality of crops. For example, 2,4-D on tomatoes has been shown to increase sugar content and decrease acidity.
The benefits of synthetic auxin analogs are clear, and this class of plant growth substances has been used extensively in commercial horticulture for many years. However, the potential hazards of their use and what governments and regulatory agencies must consider when establishing guidelines and policies regarding these products require a closer look.