What Is Auxin Definition Types Functions and Transport Mechanism
Auxins are a potent growth hormone released by plants in their natural state. They encourage cell division, stem and root growth and are present in shoot and root tips. They can also have a significant impact on plant orientation by encouraging cell division on one side of the plant in response to sunlight and gravity.
Plants require sunshine, water, oxygen, and minerals to grow and develop. There are outside influences. Aside from these, plants' growth and development are governed by certain intrinsic influences. Plant hormones, also known as phytohormones, are a form of a hormone produced by plants.
All growth and development processes, such as cell division, enlargement, flowering, seed formation, dormancy, and abscission, are regulated by plant hormones.
Plant hormones are classified into two groups based on their actions:
Plant Growth Promoters
Plant Growth Inhibitors
Auxin Definition
Auxin is a word that means "to rise." In agricultural and horticultural practices, they are widely used. They are found in the rising apices of roots and stems before migrating to other parts of the plant to perform their functions.
Natural: Indole-3-acetic acid (IAA), Indole butyric acid (IBA)
Synthetic: 2,4-D (2,4-Dichlorophenoxyacetic acid), NAA (Naphthalene acetic acid)
Auxin in Plants
Role of Auxins
Auxins stimulate shoot elongation by influencing gibberellins, which facilitate cell elongation. This lengthens the plant. Gibberellins, and thus auxins, increase the distance between nodes, allowing branch points to be spaced further apart.
Controlling Seedling Orientation
Charles Darwin and his son Francis were among the first to note the seedlings bend toward the sun. However, where auxins are located and how they affect cells inside the plant determine whether a new shoot develops into the soil or towards the light. Gravity can cause auxins to migrate downward and laterally away from light. Cells grow faster in areas of the plant where auxin levels are high.
When auxin is added to a cut stem, the stem will begin to form roots at the cut.
Auxins in the flower facilitate the maturation of the ovary wall as well as steps in the full growth of the fruit.
Auxins can be synthesized or formed naturally (by the plant) (in a lab). When synthesized, they can be used as a pesticide in high concentrations, causing rapid development. 2-4-D is an auxin-based herbicide that is specifically designed to cause dicots (plants like dandelions) to grow rapidly and uncontrollably, eventually destroying the plant.
What is Auxin Plant Hormone?
Auxin is a plant hormone derived from tryptophan, an amino acid. Auxins may be one of several molecules, but they are all involved in cellular regulation in some way. Plant hormones come in five different forms. Auxin molecules are one of them. Gibberellins, cytokinins, ethylene, and abscisic acid are the other main classes. Auxin was the first of these groups to be discovered, and it was isolated chemically in the 1930s. Indoleacetic acid, or IAA, is the most widely used auxin. IAA is an auxin that is essential for plant tissue growth and development. Scientists have been able to replicate similar structures, known as synthetic growth regulators, by studying auxin molecules.
Functions of Auxin in Plants
Stem and root cell elongation
IAA in the apical bud suppresses the development of lateral buds due to apical dominance.
Parthenocarpy, or the growth of fruit without fertilization, is induced, for example, in tomatoes.
Prevents leaves, flowers, and fruits from falling prematurely.
Useful in stem cuttings and grafting where it encourages flowering, such as in pineapples.
2,4-D is a commonly used herbicide for killing unwanted dicot weeds without harming monocot plants.
Cell division and xylem differentiation are aided by this substance.
FAQs on Auxin in Plants and Its Role in Growth Regulation
1. What is auxin in plants?
Auxin is a plant hormone that regulates growth and developmental processes in plants. The most common natural auxin is indole-3-acetic acid (IAA).
- It is mainly produced in the shoot apical meristem and young leaves.
- It controls cell elongation, root formation, and directional growth responses.
- It plays a central role in coordinating overall plant growth and development.
2. What is the function of auxin in plants?
The main function of auxin is to promote cell elongation and regulate plant growth patterns. It performs several key roles:
- Stimulates elongation of cells in stems.
- Maintains apical dominance by suppressing lateral bud growth.
- Induces adventitious root formation in cuttings.
- Controls phototropism and gravitropism.
- Delays leaf abscission in certain conditions.
3. How does auxin cause cell elongation?
Auxin causes cell elongation by activating the acid growth hypothesis, which loosens the cell wall. The process occurs in steps:
- Auxin stimulates proton pumps to release H+ ions into the cell wall.
- This lowers the pH and activates expansin proteins.
- Expansins loosen the cell wall, making it flexible.
- Water enters the cell by osmosis, causing the cell to elongate.
4. Where is auxin produced in plants?
Auxin is mainly produced in the shoot apical meristem, young leaves, and developing seeds. Key sites include:
- Tips of growing shoots.
- Young expanding leaves.
- Developing fruits and embryos.
5. What is apical dominance and how is auxin involved?
Apical dominance is the phenomenon where the main central shoot suppresses the growth of lateral buds due to auxin. In this process:
- The apical bud produces high levels of auxin.
- Auxin moves downward and inhibits lateral bud growth.
- If the apical bud is removed, lateral buds grow due to reduced auxin levels.
6. What role does auxin play in phototropism?
Auxin controls phototropism by redistributing to the shaded side of a plant stem, causing it to bend toward light. The mechanism includes:
- Light causes auxin to accumulate on the darker side.
- Higher auxin concentration stimulates more cell elongation there.
- The unequal growth causes the stem to curve toward the light source.
7. What is the difference between auxin and gibberellin?
Auxin mainly promotes cell elongation and directional growth, while gibberellin primarily stimulates stem elongation and seed germination. Key differences include:
- Auxin regulates apical dominance and tropic responses.
- Gibberellin promotes internode elongation and breaks seed dormancy.
- Auxin is central to root initiation, whereas gibberellin strongly influences flowering in some plants.
8. How is auxin transported in plants?
Auxin is transported in plants through a directional process called polar transport. This transport has two main features:
- Occurs from the shoot apex downward (basipetal transport).
- Involves specific carrier proteins such as PIN proteins.
9. What are synthetic auxins and what are they used for?
Synthetic auxins are artificially produced compounds that mimic the action of natural auxin. Common examples include:
- 2,4-D (2,4-dichlorophenoxyacetic acid)
- NAA (naphthaleneacetic acid)
- Selective herbicides to kill broadleaf weeds.
- Rooting hormones in plant cuttings.
- Agents to promote fruit development in agriculture.
10. Can you give an example of auxin’s role in fruit development?
Auxin promotes fruit development by stimulating ovary growth after fertilization. For example:
- After pollination, developing seeds produce auxin.
- Auxin stimulates the ovary wall to grow into a fruit.
- In some cases, external auxin application can induce parthenocarpy (seedless fruit formation), as seen in tomatoes.
