[Biology Class Notes] on Auxin Pdf

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.