Gibberellin Hormone - learn about its history, chemical nature and applications


Want to learn about the Gibberellin Hormone? The below article provides you with the detailed explanation of Gibberellin Hormone. Find here in this article the complete history, distribution, chemical nature and physiological effects of this hormone.

History of Gibberellins

Gibberellins are growth hormones having gibbane ring skeleton which causes cell elongation of intact plants in general and increased intermodal length of genetically dwarf plants. Gibberellins are one of the most important groups of phytohormones, noticed by some Japanese farmers in some diseased rice plants which grew abnormally tall and thin. They called it Bakanae or foolish seedling disease. Infection by a fungus, Gibberella fujikuroi (=Fusarium moniliforme) was shown to be responsible for the disease. Kurosawa (1926) performed experiments to demonstrate that filtrates of the cultures of the fungus produced the characteristic symptoms when applied to healthy seedlings of rice. In 1938, Yabuta and Sumiki succeeded in isolating a pure crystalline chemical, which they named gibberellin. Cross and others (1961) isolated six gibberellins from the fungus Gibberella fujikuroi which they named as GA1, GA2, GA3, GA4, GA7 and GA8. MacMillan and others (1961) isolate three gibberellins from bean seeds. They were termed GA5, GA6 and GA8. The number of gibberellins discovered up till now is more than 100, out of which 15 have been obtained from Gibberella fujikuroi. They are chemically known as gibberellic acid.

Distribution of Gibberellins

It was thought earlier that gibberellins are found in fungi only. But later on, the presence of this group of plant hormone was noticed in all groups of plants like angiosperms, gymnosperms, pteridophytes, mosses and algae. It is completely lacking in bacteria. As far as the distribution of this hormone in different organs of flowering plant is concerned, it has been found distributed though out the plant body. Its highest concentration is reported in seeds. Sufficient amount of gibberellins is also found in young leaves and roots. Conclusively, it has been demonstrated that comparatively higher amount of gibberellins is found in rapidly growing parts of the plant body. It is transported in all directions of the plant body.

Chemical nature of Gibberellins

The chemical nature of gibberellins was studied by Cross et al (1961). He observed that a general gibbane ring skeleton is found in all forms of gibberellins. Four carbon skeleton rings are present in a gibbane ring. These are named as A, B, C and D rings. Therefore, the gibbane ring is known as the tetra carbocyclic compound. At present, the structure of about29 gibberellins is known. Out of these, the first nineteen gibberellins are C19 compounds while remaining nine are C20 compounds. Moreover, 18 gibberellins are mono-carbocyclic, 7 are di-carbocyclic and 4 are tetra carbocyclic in nature. Minor differences in the chemical structure of different gibberellins are found.

Physiological effects and application of Gibberellins

The physiological effects and application of gibberellins are as given below:

  1. Elongation of Stem: Application of gibberellins causes elongation of internodes due to which length of plants increases. The abnormal increase in the leaf sheath size has also been observed due to gibberellin application on plants. Such changes are related to rapid cell division and cell elongation.

  2. Braking seed dormancy: It has been observed that the dormancy in buds of winter variety of potato is broken by the application of gibberellins.

  3. Parthenocarpy: Parthenocarpic fruits can easily be developed in tomato, apple, peach, etc. by gibberellin application. In these plants, gibberellin hormone has been found more effective in comparison to Auxins.

  4. Elongation of genetically dwarf plants: In certain plants, dwarfism is controlled by a single gene. Such plants are known as single gene dwarfs. Application of gibberellins like GA3 has been found to cause elongation in plants like Pisum sativum, Phaseolus multiflorous, etc.

  5. Promotion of flowering: Application of gibberellins has also been reported to cause flowering in some long-day plants (LDP) under unfavourable short-day conditions.

  6. Substitution of cold treatments: In many biennial plants, flowering is induced within a year by the application of gibberellins without any cold treatment. Thus, such plants become capable of completing their life cycle within a year instead of two.

  7. Bolting effect: many biennial plants like cabbage and Hyoscyamus niger have rosette vegetative growth in first year. In this condition, the internodes on the stem are much reduced in length. Leaves are arranged compactly on the stem. In the second year, such plants show elongation and flowering. However, it has been observed in Hyoscyamus niger (Henbane) that application of gibberellins causes much elongation of stem and flowering in the first year of growth itself. Such an effect of gibberellins on plants is called bolting effect.


Comments

Author: Umesh13 Oct 2020 Member Level: Diamond   Points : 3

This is an interesting and well-composed article on gibberellin hormone. The relation of the presence of this hormone with the growth of the plant is an interesting area and has promising potential. Such specific hormones sometimes have a value from a drug manufacturing point of view as many drugs are synthesized from such unique materials by carrying out further research and investigation in the matter. If a particular chemical or hormone is able to affect the plants which are also a type of living beings, then there is scope for it to transform it to the use of humans or animals in some way.



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