Iaa Hormone

IAA or Indole-3-acetic acid is a plant growth regulator or hormone, belonging to the class of Auxin. It is naturally occurring and imparts physiological effects, regulating plant growth and development. Additionally, it is also found in some bacteria and fungi, where it controls gene expression and various physiological responses.

Charles Darwin and his son Francis Darwin observed phototropism in the coleoptiles of canary grass and concluded that some substance present at the tip of the coleoptile influenced the bending of the coleoptile. This discovery marked the first plant hormone to be discovered, known as auxins. Later, F.W. Went was able to isolate auxins from the coleoptiles of oat seedlings and even from human urine.

Structure and Characteristics

IAA (Indole-3-acetic acid) is an indole derivative containing an indole ring with a carboxymethyl substituent. Its structure is similar to that of tryptophan.

Indole-3-acetic acid

IAA is synthesized in plants by various biochemical pathways, primarily initiated by the amino acid tryptophan. Environmental factors such as pH and temperature can impact IAA biosynthesis. Additionally, IBA (indole butyric acid) is a naturally occurring auxin in plants.

Physiological Effects

The Main Effects of IAA

  1. Regulation of Plant Growth and Development
  2. Cell Division
  3. Elongation
  4. Differentiation

IAA (Indole-3-acetic acid) is the primary auxin present in plants and it plays an important role in regulating cell expansion, differentiation, and division.

IAA promotes apical dominance by inhibiting the growth of lateral or axillary buds. It is present in the apical bud and acts to inhibit the growth of lateral buds.

IAA is responsible for phototropism and responding to gravity.

IAA initiates both primary and lateral root formation.

The International Association of Anthocyanins (IAA) also regulates leaf morphogenesis.

IAA is also involved in studying plant-pathogen interactions and the defense mechanisms of plants.

IAA plays an important role in plant gene regulation and stress response.

Exogenous application of IAA and other auxins is widely used in agriculture and horticulture.

They encourage rooting in the stem cuttings and foster blooming.

They promote abscission of mature leaves and fruits, but prevent premature falling of them.

Auxins play a role in regulating xylem differentiation.

IAA and other auxins can interact with other plant regulators either synergistically or antagonistically. For example, the ratio of auxin to cytokinin in the culture medium can determine whether root or shoot buds are initiated.

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