Plant Growth Regulators

Plant growth regulators (PGRs), also known as plant hormones, are chemicals that significantly influence the growth and development of plants. These substances can be naturally occurring or synthetically produced and play crucial roles in regulating a wide range of physiological processes, including cell division, elongation, flowering, fruiting, and responses to environmental stimuli.

Types of Plant Growth Regulators :


  • Role: Auxins are primarily involved in cell elongation, root initiation, and branching. They influence phototropism (growth towards light) and gravitropism (growth in response to gravity).
  • Example: Indole-3-acetic acid (IAA) is a common natural auxin.
  • Applications: Auxins are used in horticulture for rooting cuttings and controlling fruit set and drop.

Gibberellins (GAs):

  • Role: Gibberellins promote stem elongation, seed germination, and flowering. They break seed dormancy and stimulate enzyme production during germination.
  • Example: Gibberellic acid (GA3) is one of the most studied gibberellins.
  • Applications: GAs are used to improve fruit size, promote seedless fruit development, and enhance the malting process in brewing.


  • Role: Cytokinins promote cell division and differentiation, delay leaf senescence, and work in conjunction with auxins to influence apical dominance and lateral bud growth.
  • Example: Zeatin and kinetin are natural cytokinins.
  • Applications: Used in tissue culture to induce shoot proliferation and in agriculture to increase crop yield and delay aging of leaves.


  • Role: Ethylene regulates fruit ripening, leaf abscission, and flower wilting. It is a gas at room temperature and acts as a signaling molecule in response to stress.
  • Example: Ethylene itself is the active compound.
  • Applications: Used to synchronize fruit ripening in crops like tomatoes and bananas and to promote flower opening.

Abscisic Acid (ABA):

  • Role: ABA is involved in seed dormancy, stress responses (especially drought and cold tolerance), and stomatal closure to prevent water loss.
  • Example: Abscisic acid (ABA) is the naturally occurring compound.
  • Applications: Used to enhance stress resistance in crops and manage seed dormancy in nurseries.

Functions and Mechanisms of Plant Growth Regulators :

  • Cell Division and Elongation
  • Apical Dominance and Lateral Growth
  • Flowering and Fruiting

Applications in Agriculture and Horticulture :

  • Crop Yield Improvement
  • Seed Germination and Dormancy
  • Fruit Ripening and Quality
  • Tissue Culture and Micropropagation

Plant growth regulators are powerful tools in modern agriculture and horticulture, offering diverse applications to enhance plant growth, productivity, and stress resilience. Their judicious use, guided by scientific understanding and regulatory frameworks, can significantly contribute to sustainable agricultural practices and food security.

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