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Gibberllins

Gibberellins
As early as 1926, Japanese investigators, while studying a disease of rice caused by Gibberella fujikuroi (Saw) Wr. (imperfect state of Fusarium

Biochemical
moniliforme Sheld), discovered that leaves and stems of infected plants showed abnormal growth. The infected plants were usually taller than the healthy ones. They called the infection as 'Bakanae' disease, literally mean­ing foolish seedlings. Subsequently, a purified preparation containing highly active crystalline material was obtained from culture filtrates of the fungus which was named as gibberellin.

When applied to healthy plants, the crystalline material reproduced the symptoms of the disease. These initial findings led to the subsequent purification of several fractions of the original gibberellin and today fourteen gibberellins have been iden­tified and many of them are available on the market for experimental and commercial purposes. Some of the gibberellins are known to be natural components of plants controlling their growth activities, dormancy, flow­ing and responses to light and temperature. Among the several gibberel­lins, GA1 was probably the first to be identified both from the fungal medium and also from higher plants. Subsequently, GA2, GA3, GA4, GA7, and GA9 were identified from the fungal medium and GA5 GA6 and GA6 from flowering plants

Several bacteria, actinomycetes and fungi are known to produce gib­berellins or gibberellin-like substances. The bacterial genera are Arthrobac­ter, Azospirillum, Azotobacter, Bacillus, Brevibacterium, Flavobacterium, Pseudomonas and Rhizobium. The actinomycetes come under the genera Ac­tinomyces and Nocardia. The fungal genera capable of producing the plant growth regulator are Alternaria, Aspergillus, Fusarium, Gibberella, Penicillium, Rhizopogon, Rhizopus, Sphaceloma and Suillus.
Some of the roles attributed to gibberellins are: (1) they overcome dor­mancy and dwarfism in plants; (2) they induce flowering of some photoperiodically sensitive and other low temperature dependent plants; (3) they alter the sex of flowers and contribute to fruit setting; and (4) they stimulate stem growth and at the same time suppress the growth of lateral branches

 
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