By: N. Shreya Mohan (MSIWM042)

Plant hormone, also known as phytohormones are signal mediated molecules produced by plants commonly controlling plant growth aspects such as defense mechanisms, stress tolerance, metabolism, reproduction and size. Hormones are elated within the plant by utilizing four types of movements. For localized movement, cytoplasmic streams within cells where delayed diffusion of ions and molecules between the cells are utilized. Vascular tissues are used to commute hormones from one part of the plant to another. These include phloem that move sugars from the leaves to the roots and flowers, and xylem that moves water and mineral solutes from the roots to the foliage of the plant respectively.

We will ponder over the major 5 plant hormones systematically and briefly-

  • AUXINS– This hormone particularly takes part in cell enlargement, cell growth bud formation. It was the first hormone to have been discovered among the “big 5”. In collaboration with other hormones, auxins promote control the growth of stems, roots etc. It is primarily produced in certain parts of plants that are actively growing such as the stem. Auxins act in such a way that it inhibits growth of buds lower than the stem. This phenomenon is the apical dominance. In seeds, they promote certain protein synthesis, to which they develop after inside the flower after pollination resulting in fruit production. The most common found of auxin in plants are indole-3-acetic acid
  • GIBBERELLIN- These set of chemicals are produced naturally by the plants and fungi too. It was first discovered by Japanese researchers where they noticed a certain chemical compound caused by a fungus called Gibberella fujikuroi that produced abnormal growth and falling over in rice plants. The chemical causing this was isolated and named Gibberellin ever since. They play a vital in plant life by making the stems longer by elongating the nodes between the stems. They are also required by the pollen during the process of fertilization.
  • ABSCISIC ACID- Also known as the ABA. The chemical is usually abundant in chloroplast, thereby produced in the leaves of the plants particularly when the plant is under stress. It acts as a plant growth inhibitor and affects bud and seed dormancy. Without ABA, the seed would grown in warm temperatures during winters and can get killed if frozen. Therefore, plants start off as a seed with high concentrations of ABA. During water stress, ABA plays a pivotal role in plants. The water deficient plant sends a signal in via the root to the leaves, causing the ABA precursors to act and move back to roots, which ultimately closes the stomata from further transpiring.
  • CYTOKININS- These group of chemical compounds are responsible for shoot formation and cell division. They are also responsible for mediating auxin transport throughout the plant. They also help delay senescence. They were initially named kinins as they were isolated from yeast. Cytokinin counter the apical dominance as created by auxins. They, with conjunction with ethylene promotes abscission of leaves, flowers.
  • ETHYLENE-It is readily found in fast and dividing cells. They have very little solubility because they are gaseous in nature thereby diffusing easily from the plant. The concentration of ethylene depends on the amount of it diffusing and leaving the plant. The main role of ethylene is fruit ripening.


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