Plant Growth regulators and Uses

Plant Growth regulator

Growth Regulators

The growth differentiation and organogenesis of tissue occurs only on the addition of one (or) more of these hormones to the medium. (Plant Growth regulator)
1.  Auxins 
auxin is a series of plant hormones that govern growth, promoting cell elongation in stems in particular. Auxins are also involved in cell division and differentiation, fruit development, root formation from cuttings, lateral branch inhibition (apical dominance), and leaf fall (abscission).
Auxins are a group of naturally occurring and synthesised substances that promote growth, however they are not always as effective as IAA. Some of these molecules, on the other hand, resist enzymatic degradation, which is IAA’s natural fate inside the plant; this property is useful in study and horticulture since auxin activity may be extended. In horticulture, agriculture, home gardening, and plant science, natural and synthetic auxins are used to promote roots, fruit setting, fruit thinning, and fruit drop management. Other auxin-like chemicals are employed as selective weed killers (e.g., to disrupt dicotyledonous plant leaf development in monocotyledonous cereal crop fields or lawns) and as leaf-removal agents in dicotyledonous plants (defoliating agents).
■Commonly used auxins are
IAA (Indole 3-Acetic Acid)
IBA (Indole 3-Butyric Acid)
2,4-D (Dichloro Phenoxy Acetic Acid)
NAA (Naphthylene Acitic Acid)
NOA (Naphthoxy Acitic Acid)
The 2,4-D is used for callus induction where as the other auxins are used to root induction.
2.  Cytokinins
Cytokinins promote cell division by sustaining protein synthesis, which is necessary for mitosis. The term Mitosis refers to a non-sexual cell division that happens in all living organisms in order to create more cells for body expansion. Every day, mitosis occurs, replacing damaged cells and allowing them to develop. When you’re harmed and lose your skin off your knee, it’s the same mitosis that aids in the regeneration of all the cells you’ve lost and gives you back your skin.

Plant growth is controlled by mitosis. (Plant Growth regulator)


  • Plant cell division and development are aided by this substance.
  • Farmers use it to boost the yield of their crops.
  • Even under drought circumstances, when sprayed to cotton seedlings, it resulted in a 5-10% increase in yield.
  • By promoting resistance to some disease-causing bacteria, it plays a key role in plant pathogenesis.
●Commonly used Cytokinins are
  • BAP (6-Benzylamino purine)
  • BA (Benzy adenine)
  • 2ip (Isopentyl adenine)
  • Kinetine (6-furfur aminopurine)
  • Zeatin (4-hydroxy 3 methyl trans 2 butinyl aminopurine)
3. Gibberellins and Abscisic acid
Seed heteromorphism, which is seen in many halophytes, is an adaptation to high salinity. However, under salt stress, the link between heteromorphic seed germination and germination-related hormones is yet unknown. The roles of gibberellins (GAs) and abscisic acid (ABA) in regulating germination of Suaeda salsa dimorphic brown and black seeds under salinity were elucidated by studying the kinetics of the two hormones during germination of the two seed types with or without salinity treatment to gain insight into this relationship. (Plant Growth regulator)
Brown and black appear to be at distinct stages of development, according to morphological study. The amount of ABA in dry brown seeds was larger than in black seeds, but it reduced following imbibition in water and salt solutions. Salt stress increased the buildup of ABA in both germinating seed types, with black seeds having a greater induction impact than brown seeds. Under both water and salt stress, black seeds had a lower germination % than brown seeds, which might be attributable to their increased ABA sensitivity rather than the difference in ABA concentration between black and brown seeds. In dry or germinating water or salt solutions, bioactive GA4 and its biosynthetic precursors were found in higher concentrations in brown than black seeds, whereas deactivated GAs were found in higher concentrations in black than brown seeds.
High salinity hindered seed germination by lowering GA4 levels in both black and brown seeds, with the effect of salt stress on GA4 levels in black seeds being stronger than in brown seeds. Higher GA4 content and sensitivity, as well as lower ABA sensitivity, contributed to the higher germination percentage of brown seeds in water and salinity; increased ABA content and sensitivity, as well as decreased GA4 content by salinity, were more profound in black than brown seeds, resulting in lower germination of black seeds in salinity. Salt stress differentially regulates ABA and GA homeostases in dimorphic seeds, which might give a method for S. salsa plants to thrive in harsh environments.
4. ABA
Abiotic stress is a major challenge to meeting the world’s agricultural output requirement in the next decades. Stress causes plants to slow down their growth and development, which has an impact on production. Plants produce a variety of stress mechanisms to cope with the magnitude of stress challenges, but this is insufficient to safeguard them. As a result, a variety of approaches have been attempted to develop abiotic stress tolerance in agricultural plants, with abscisic acid (ABA) phytohormone engineering being one of the most promising. (Plant Growth regulator)
ABA is an isoprenoid phytohormone that regulates a variety of physiological processes from stomatal opening to protein storage and allows plants to respond to a variety of conditions such as drought, salt, and cold. ABA is also known as an essential messenger since it serves as a signalling mediator in plants’ adaptive responses to various environmental stressors. The role of ABA at the molecular level in response to abiotic stress, as well as ABA signalling, will be discussed in this paper. The effect of ABA on gene expression is also discussed in the paper.
5. Ethylene
Ethylene is a class of plant growth regulators that are frequently used to speed up the ripening of fruits and increase the number of blooms and fruits produced.

Ethylene is a tiny hydrocarbon gas that is colourless and combustible and has the formula C2H4 or H2C=CH2. The IUPAC term for ethylene is ethylene. When it’s fresh, it smells “sweet and musky.” C2H2 is the most basic alkene and the second most basic unsaturated hydrocarbon.

Ethylene is widely utilized in the chemical industry, and it is employed extensively in the production of polyethene. Furthermore, ethylene is employed in agricultural techniques such as ripening fruits, seed germination, and so on. (Plant Growth regulator)

Function of Ethylene

The following are some of ethylene’s most important functions:


Ethylene promotes horizontal development as well as axis swelling. It stops development in the longitudinal direction.


It makes you less sensitive to gravity. The leaves and flowers droop, and the stems become positively geotropic.


It hastens the ageing of flowers and foliage.


Ethylene causes the plant’s flowers, leaves, fruits, and other components to abscise. It aids in the development of hydrolases.

Dominance at the Apex

It enhances apical dominance and prolongs the dormancy of lateral buds.

Breaking the Doldrums

It awakens seeds, buds, and storage organs from their slumber.

Fruit maturation

Ethylene causes climacteric fruits like bananas, mangoes, and apples to ripen artificially.


Ethylene causes pineapple and mango trees to blossom. It also causes bloom fading in some plants.

Ethylene’s Applications

The following are some of the most important applications for ethylene:

  • It is employed as a plant growth regulator since it modulates a variety of physiological processes.
  • Ethylene lamps are used to develop the colour of fruits like bananas, mangoes, and apples, as well as to ripen them.
  • It has a feminising impact on plants, which means it is used to increase the amount of female flowers in a plant in order to get it to fruit.
  • It is used to encourage early sprouting in rhizomes, tubers, and seeds.
  • It’s used to thin out superfluous blossoms and immature fruits like walnuts, cherries, cotton, and so on. (Plant Growth regulator)

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