07 Plant Growth and Mineral Nutrition - part 10 - Growth harmone - Gibberellins

07 Plant Growth and Mineral Nutrition - part 10 - Growth harmone - Gibberellins


Gibberellins : 
  • It is another growth promoting hormone and is abundant in root tip and developing seeds. 
  • It shows non-polar transport through vascular tissue. 
  • Gibberellins were first isolated from the fungus Gibberella fujikuroi by Japanese scientist Kurosawa (1926). 
  • He observed that when rice plant was infected by fungus Gibberella fujikuroi, it shows extensive stem elongation called`bakane disease'. 
  • The crystalline form of Gibberellins were isolated by Yabuta and Sumiki (1938) from the fungus culture. They named it as gibberellin. 
  • It is synthesized in young leaves, seeds, roots and stem tips. These are synthesized from mevalonic acid. 
  • More than 150 chemical types are known so far. 
  • GA3 is most common and biologically active form. 
  • Chemically it contains a gibbeane ring a cyclic diterpene with four isoprene units. 
Physiological effects and application of Gibberellins : 
  • Dormancy of bud can be broken by gibberellin treatment. 
  • It can promote seed germination in cereals likebarley and wheat by synthesizing hydrolysing enzyme amylase to produce sugar. 
  • The most striking effect of it, is the elongation of stem where internodes increase in length. 
  • It also promotes bolting i.e. elongation of internodes just prior to flowering in plants those with rosette habit e.g. beet, cabbage. 
  • It causes parthenocarpy in tomato, apple and pear, and flowering in long day plants. 
  • It is used to increase the fruit size and bunch length of grapes. 
  • When gibberellins are applied on genetically dwarf plants like maize, the stem rapidly elongates and acquires the height of normal tall varities of maize. 
  • Application of gibberellins overcomes the requirement of vernalization. 
Application : 
  1. It inhibits growth of root
  2. Delays senescence and prevents abscission.
  3. Breaks dormancy of seed and hastens germination. 
  4. Causes production of male flowers on female plant.

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