We felt it was only right that we provided an explanation of the blog’s namesake, so here it is!
Gibberellins are plant hormones that were first isolated in 1935 from the fungus Gibberella fujikuroi. GA’s cause a multitude of different physiological and morphological effects; including stimulating growth, promoting flowers and even inducing dormancy in some species. Effects are very much dependent on the concentration of the hormones and the species in which they are found. For the sake of brevity in this blog post I will be largely focusing on Gibberellic acid’s effect on growth.
One of the most striking effects caused by GA is the marked increase in stem elongation, indeed an observation of this sort initially lead to the discovery of gibberellins. Japanese scientists observed that the rapid growth in diseased rice seedlings was caused by a parasitic fungus known as Gibberella fujikuroi. The afflicted plants were twice the height of those unaffected and the leaves were chlorotic and thin. The disease is known as bakanae (馬鹿苗病) or if you translate the kanji “foolish seedling disease”. The Japanese scientists concluded that a fungus metabolite must be the cause of the abnormal growth and thus proceeded to attempt to isolate the substance. They did so successfully in 1935 and hence chose to name the hormone after the fungus.
How do they work?
Gibberellins alter gene transcription within plants; they cause the destruction of DELLA through the activation of proteomes. DELLA is thereby prevented from binding to the gibberellin dependent transcription factors and inhibiting gene transcription. Henceforth gene transcription can occur. To put it more simply Gibberellins inhibit the inhibitor and therefore growth repression is relieved.
Applications?
Naturally practical applications for GA where immediately sought. Brian and Hemming (1955) discovered that dwarf pea plants could be brought to normal height through the application of GA, results obtained however, were not uniformly the same amongst other dwarf varieties in peas; demonstrating the unpredictability of the hormone. Greater success was found in the application of the hormone to grapes- in particular the Thompson seedless variety. Professor Robert J. Weaver of the University of California discovered when the variety was sprayed with gibberellin, berry size increased.
The number of gibberellins that have been identified so far is 126. It is clear that there is far more to learn about GA’s effects on plants and potential applications. I look forward to learning more about them and I will keep you updated on any more revelations in the field I find!
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