Indole-3-acetic acid

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Indole-3-acetic acid (IAA) is a naturally occurring plant hormone in the auxin family. It is the most common, naturally occurring, plant growth hormone of the auxin class. IAA has a crucial role in coordinating many growth and behavioral processes in the plant's life cycle and is essential for plant development.

Biosynthesis

IAA is synthesized in plants from the amino acid tryptophan through several pathways. The primary pathways include the indole-3-pyruvic acid pathway, the tryptamine pathway, and the indole-3-acetonitrile pathway. These pathways involve various enzymes and intermediates, leading to the production of IAA.

Functions

IAA is involved in various plant growth processes, including:

• Cell elongation: IAA promotes the elongation of cells in the stem and other parts of the plant.
• Apical dominance: IAA is responsible for maintaining the dominance of the apical bud over the lateral buds.
• Root initiation: IAA stimulates the formation of adventitious roots and lateral roots.
• Fruit development: IAA plays a role in the development of fruits and the regulation of fruit ripening.
• Tropisms: IAA is involved in phototropism and gravitropism, helping plants to grow towards light and against gravity.

Mechanism of Action

IAA functions by binding to auxin receptors such as TIR1 and ABP1. This binding triggers a signaling cascade that leads to the activation or repression of specific genes involved in growth and development. The auxin response factors (ARFs) are key players in this process, regulating the expression of auxin-responsive genes.

Transport

IAA is transported throughout the plant via two main mechanisms:

• Polar auxin transport: This is a directional transport mechanism that moves IAA from the apex of the plant towards the base.
• Non-polar transport: This involves the movement of IAA through the phloem and other tissues.

Applications

IAA is used in agriculture and horticulture to promote root growth, improve crop yield, and enhance plant propagation. Synthetic auxins, such as 2,4-Dichlorophenoxyacetic acid (2,4-D), mimic the effects of IAA and are used as herbicides.

See also

• Auxin
• Plant hormone
• Tryptophan
• Cell elongation
• Apical dominance
• Root initiation
• Fruit development
• Phototropism
• Gravitropism

External links

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