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The growth inhibiting hormone in plants is

The growth inhibiting hormone in plants is Correct Answer Abscisic acid

Concept-

  • Plant growth hormones or phytohormones are simple molecules with complex chemical composition, that regulates the growth and physiology of plants.
  • Based on their functions on the living plant body, they can be classified into two groups-
    • Plant growth promoters - Eg. Auxins, Gibberellins & cytokinins.
    • Plant growth inhibitors -Eg. Abscisic acid.
  • Gaseous PGR like ethylene can be put into both groups, however, it is largely an inhibitor of growth activities.

Explanation-

  • Abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy.
  • But like other PGRs, it also has other wide-ranging effects on plant growth and development.
  • It acts as a general plant growth inhibitor and an inhibitor of plant metabolism.
  • ABA inhibits seed germination.
  • ABA stimulates the closure of stomata and increases the tolerance of plants to various kinds of stresses.
  • Therefore, it is also called the stress hormone.
  • ABA plays an important role in seed development, maturation and dormancy.
  • In most situations, ABA acts as an antagonist to GAs.

Therefore the growth-inhibiting hormone in plants is Abscisic acid.

Additional Information

Auxin

  • Auxins (from Greek ‘auxein’ to grow) were first isolated from human urine.
  • The term ‘auxin’ is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth-regulating properties.
  • They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action.
  • Auxins like IAA and indole butyric acid (IBA) have been isolated from plants.
  • NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are synthetic auxins.
  • All these auxins have been used extensively in agricultural and horticultural practices.

Cytokinins

  • Cytokinins have specific effects on cytokinesis and were discovered as kinetin (a modified form of adenine, a purine) from the autoclaved herring sperm DNA.
  • Kinetin does not occur naturally in plants.
  • Search for natural substances with cytokinin-like activities led to the isolation of zeatin from corn kernels and coconut milk.
  • Since the discovery of zeatin, several naturally occurring cytokinins, and some synthetic compounds with cell division promoting activity, have been identified.
  • Natural cytokinins are synthesized in regions where rapid cell division occurs, for example, root apices, developing shoot buds, young fruits, etc.

Gibberellins

  • Gibberellins are another kind of promotory PGR.
  • There are more than 100 gibberellins reported from widely different organisms such as fungi and higher plants.
  • They are denoted as GA1, GA2, GA3, and so on.
  • However, Gibberellic acid (GA3 ) was one of the first gibberellins to be discovered and remains the most intensively studied form.
  • All GAs are acidic.
  • They produce a wide range of physiological responses in the plants.

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