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Question : How were different plant growth regulators discovered ?

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Solution :The discovery of all five major groups of plant growth regulators have been done accidentally
Discovery of Auxin :
This was the first growth hormone to be discovered.
They observed the coleoptiles of canary grass that responded to unilateral illumination by growing towards the source of light [Phenomenon known as photo periodism].
After performing series of experiments they came to the conclusion that coleoptiles tip was the site that has the property of transmittable inference due to which bending of complete coleoptiles was caused.

The first PGR in auxin was isolated by F.W. Went in 1928 from coleoptile tip of oat seedlings.
Discovery of Gibberellins :
In early part of `20^(th)` CENTURY, the bakane [foolish seedling) was reported to be caused by a fungal pathogen Gibberella fugikuroi, symptoms shown by the plant were elongated stems, little or no production of grains and plant become weak thus, it was later identified that the active substances was gibberellic acid.
The Japanese plant pathologist E. Kurosawa reported the appearance of symptoms of the disease in uninfected rice seedlings when they were treated with sterile filtrates of the fungus.
Discovery of Cytokinins :
E SKOOG and his co-workers while studying the nutritional requirements of tissue culture derived from the internodal segments of tobacco stems, observed that from that internodal SEGMENT (i.e., a mass of undifferentiated cells) proliferated only when the nutrient medium containing auxin was supplemented with the extract of vascular tissues or yeast or coconut milk (Water of endosperm of coconut) or DNA.
It was later found that the active substances were a MODIFIED form of adenine which was crystallised and identified as kinetin.
Further the compounds that exhibited kinetin like properties were termed as cytokinins.
Discovery of Abscisic Acid :
With the progression in the research on plant growth regulators three independent researchers reported the purification and chemical characterization of three kind of inhibitors (during mid 1960) i.e., inhibitor-B, abscission II and dormin.
Later, three were proved to be chemically IDENTICAL in nature and were named Abscisic Acid [ABA]
Discovery of Ethylene : Cousins [1910] confirmed the release of a volatile substance from ripened oranges that enhance the ripening of stored unripened bananas.
This volatile substance was later identified to be a gaseous plant growth regulators.


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