Plant Hormones

Plant Hormones


  • Auxins are plant hormones essential for plant growth.
  • They principally control cell enlargement and differentiation which results in growth and elongation.
  • Auxins are responsible for phototropism, the growth of a plant towards light, and geotropism, growth direction determined by gravity.
  • An example of an auxin is Indole-3-acetic acid (IAA), which stimulates the elongation of cells within young developing shoots.
  • Overusing auxins can result in inhibited growth and an abnormal plant morphology.


  • Gibberellins are another type of plant hormone that facilitate stem elongation, germination, flowering, and fruit development.
  • They are involved in breaking dormancy, the period during which a plant pauses growth.
  • Gibberellins cause an increase in length of the stems by stimulating cell division and elongation.
  • They also promote rapid stem and root growth and are key to the bud formation process.

Abscisic Acid (ABA)

  • Abscisic Acid (ABA) is known as the stress hormone in plants.
  • It plays a vital role in initiating and maintaining seed and bud dormancy.
  • ABA facilitates the closure of stomata in situations of water stress to prevent water loss.
  • It also suppresses growth, ensuring the plant can survive under stressful conditions.


  • Ethylene is a small, gaseous plant hormone that guides ripening of fruits, opening of flowers, and shedding of leaves.
  • Ethylene is the only known plant hormone to transmit as a gas.
  • Its key role is in fruit ripening - it speeds up the process and is used commercially to ripen fruits like tomatoes and bananas after they’ve been picked.

Plant hormones are crucial to the growth and development of plants. They control many aspects such as growth rate, reaction to environmental stresses, and various developmental processes, including germination, dormancy, flowering, sex expression, and fruit ripening. Understanding these hormones can help improve agricultural practices and crop yield.