Phytohormones (Hormones in Plants)

Phytohormones (Hormones in Plants)
Hormones are organic compounds which generated in very small amounts and affect on physical activities. These activities occur in distant places from where generated. Affect of a hormone may be negative or positive. They catalyse some physical activities and negate some.

In animals, hormones are generated in exact places and they do only it. But in plants, there are no such exact tissue to generate hormones. There are five (5) main types of hormones in plants.

Those are,
  1. Auxin
  2. Cytokinins
  3. Gibberellins
  4. Ethylene
  5. Abscisic acid (ABA)

Auxin is the very first discovered phytohormone and it is hundred years ago. Auxin controls the elongation of the stem of grass and small plants. One of the known auxins is Indole - 3 - acetic acid (IAA). This generates in tips of the buds and transport downwards using phloem. This is similar in structure to the amino acid called tryptophan. This also generated by tryptophan in plants.
Functionality of IAA:

  • Inactivate partial buds.
  • Turn the stem towards the light.
  • Increase the ability of grow roots in cut stems
  • Stops creating the abscission layer
  • Stimulate the elongation of cells by increasing the flexibility of cell walls.
  • Increase the growth of fruits.
  • Increase the growth of vascular cambium.
Gibberellins generated in tips of stems and roots, and immature leaf buds. Functionalities are,

  • improving the stretching of stem
  • increasing cell growth
  • help to break dormancy of seeds
  • improve germination
  • improve parthenocarpy
  • break the dormancy of shoots
Stimulates the cell division. Slow the ageing and withering of leaves.

Abscisic acid
Generated in mature green leaves, fruits, root end caps, seeds. This is a negate type. This increases dormancy of buds and seeds. Increase the ageing of leaves. Increase the falling of leaves and fruits.

Increasing the ripening of fruits, increasing the flowering, reducing the elongation of stem and roots, help to generate the abscission layer.
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