Plant Hormones

What are Plant Hormones?

Hormones are one of the essential elements for living beings which includes plants too. Hormones are the chemical messenger that is produced at a specific place, send to the target destination for their work.

Likewise, in humans, hormones are naturally produced in plants also. These hormones regulate plant growth, their response to the environment, and certain other activities.

As said above, hormones are synthesized at one part and then sent to other parts of the plants, where they receive signals from the target tissue to take action or respond accordingly which can be of fruit ripening, growth, respond to stimulus, flowering, root growth, stem elongation, leaf fall or leafing, organs regulations, etc.

These hormones are also ‘plant growth regulators‘ as they have the potential to inhibit or stimulate plant growth.

Plant Hormones

There are five naturally occurring plant hormones, like – auxin, gibberellins, cytokinin’s, and ethylene, abscisic acid.


The most crucial hormone of the plant is the Auxin, which is engaged in the plant-cell elongation, rooting, and apical dominance. One of the known auxins is IAA or Indoleacetic acid, which is manufactured in the apical meristem of the shoot. IAA promotes developing fleshy fruits when this hormone is present in the growing seeds.

Therefore, auxin is considered as the power booster for the root and shoot elongation along with the factor that encourages leaf cells to grow. Moreover, we can say that auxin is involved in plant growth in numerous ways, like:

  • Growth of root in downward direction i.e. towards gravity (geotropism).
  • Planting bending towards the light (phototropism).
  • Flower formation.
  • Fruit growth and development.
  • Formation of adventitious roots.
  • Promoting the apical dominance (the potential of the apical bud to such hormones that inhibit the growth of buds below the stem).
  • Play role in cell division and differentiation


Cytokinins are present in plants as well as in animals, their role in plants are:

  • Delay cell-aging, cell death (senescence).
  • In combination with auxin, they stimulate the growth of roots.
  • They also promote cell division.


This hormone is abundantly present in seeds and in young roots and leaves as well. It has been found that gibberellins play a vital role in the growth of the main stems

Gibberellins are involved in:

  • Break seed dormancy.
  • Cell- division and dormancy.
  • Seed germination.


One of the unique hormones, present in the gaseous form, play a major role in:

  • Fruit ripening.
  • A major reason for epinasty (leaves to droop) and drop (abscission).
  • Supports cell senescence.
  • The production of ethylene gets increased in response to stress and even it is found at high concentrations when the plant’s life is at the ending stage.

Abscisic acid

  • Abscisic acid or ABA is the plant-growth inhibitor, that inhibits early dormancy.
  • Prevents seeds germination.
  • Cause the abscission or detachment of flowers, fruits, and leaves.
  • Responsible for the closing of stomata.

Plant growth regulators can be also be synthetically produced as per the need like, Indolebutyric acid (IBA) is also the type of auxin that works for the root growth.

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