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:
Hakimuddin Kuwakhedawala is based in India with over 15 years experience as a teacher. Teaching and writing are his passion. Most of the articles of Hakimuddin are related to education, exam, environmental problems, etc.
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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.