Physiological Effects of Plant Growth Regulators – Class 11 | Chapter – 15 | Biology Short Notes Series PDF

Physiological Effects of Plant Growth Regulators: In the beginning, human urine was used to separate auxins (from the Greek ‘auxin’: to grow). Indole-3-acetic acid (IAA) and other naturally occurring and synthesized substances with specific growth-regulating properties are referred to as “auxins.” properties. They are typically created by the stems’ expanding apices, roots from which they spread to the areas where they act. 

Physiological Effects of Plant Growth Regulators

Plant regulators are divided into 2 types according to their working mechanism:

Plant Promoter

These are those hormones that promote the growth of the plant. The promoter hormones include:

  • Auxin 
  • Gibberellin
  • Cytokine

Plant Inhibitor

These are those hormones that inhibit the growth of the plant. The promoter hormones include:

  • Abscisic Acid
  • Ethylene


Isolated plant compounds include indole acetate (IAA) and  IBA 2, 4-D and NAA   are artificial auxins. 

  • These auxins have all been widely utilized in practices used in horticulture and agriculture. 
  • They aid in the process of stem cutting roots, which are frequently utilized for plant multiplication. For example, auxins encourage flowering in pineapples.
  • Early on, they assist in preventing fruit and leaf drop, but they also encourage the
  • older, which would be mature leaves, and also the fruit would be falling off.
  • The developing apical bud in case of the plants which are higher prevents the expansion of
  • a process known as apical dominance affects the lateral (axillary) buds.
  • Decapitation of shoot tips typically causes the formation of lateral buds.
  • Additionally, auxins cause parthenocarpy, such as in tomatoes. They’re frequently employed as herbicides.
  • 2, 4-D, a popular herbicide for dicotyledonous weeds, doesn’t impact mature trees’ monocotyledonous vegetation. It is utilized to make gardeners maintain weed-free lawns. 
  • Also, auxin regulates xylem differentiation and aids in the division.


  • A different class of promoter PGR is gibberellin. Hundreds of gibberellin would be reported from numerous diverse organisms, including such as higher plants and fungus. They are marked.
  • as GA1, GA2, GA3. So forth. However, Gibberellin (GA3) acid was among the initial only gibberellin that would be discovered and the most carefully analyzed form. Each GA is acidic. They create a variety of plants’ physiological reactions. 
  • Their capacity to stimulate growth Grape stem length is increased by lengthening the axis. Gibberellins, cause fruits to enlarge and their shape would be improved, such as apples. 
  • They also wait for senescence. As a result, the fruits would be on the tree for longer to extend the era of the market. 
  • GA3 is applied to expedite the brewing process of the malting industry.
  • In the stems of sugarcane, carbohydrates are stored as sugar. gibberellins are sprayed on sugarcane crops to lengthen the stems up to a 20-ton per-acre increase in the yield.
  • Spraying GAs on young conifers accelerates the maturation process, so resulting in early seed germination. Bolting is also encouraged by gibberellins (internode elongation before blooming) in beet, cabbage, and many other plants that form rosettes.


  • Cytokinins, which were first identified as kinetin (a purine-modified version of adenine), were found in the DNA of autoclaved herring sperm and would have some specific effects on the cytokinesis. Plants do not naturally produce kinetin. 
  • Look for organic Zeatin was isolated from zeatin-like compounds that had cytokinin-like properties in coconut milk with maize kernels. 
  • Since zeatin’s discovery, numerous cytokinins that occur naturally as well as some manufactured substances that have cell activities that promote division have been discovered. The term “natural cytokinins” is synthesized in areas with a high rate of cell division, such as the root immature fruits, growing shoot tips, and apices. 
  • It promotes the growth of lateral shoots, chloroplasts in leaves, and adventitious shoot production. 
  • The cytokinins aid in reversing apical dominance. 
  • They encourage the mobilization of nutrients, which helps to postpone leaf senescence.


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By Team Learning Mantras