Plant Growth Regulators (PGRs)

Plant Growth Regulators, also sometimes reffered to as plant growth hormones, refers to a group of chemicals, both naturally occouring and synthetic, that are used in plant cell culture media to facilate plant growth. Plant Growth Regulators are broadly divided into three groups: Auxins, Cytokinins, and Other Plant Growth Regulators. Most plant cell culture media include, at the very least, one auxin and one cytokinin.

Auxins
Generally speaking Auxins are responsible for promoting cell enlargement and root initiation. But individual auxins have varying effects on plant tissue. Auxins were first discovered by Dutch biologist Frits Warmolt (F.W.) Went in 1928. Went, throughout his career, researched the effects of plant hormones and synthetic plant hormones on plant growth. In 1928, Went observed that by extracting a substance from the tips of oat coleoptiles (a sheath protecting young grass shoots) he could induce phototropic responses (the action which causes a plant to grow towards a light source) in coleoptiles that had their shoot tips removed, and were therefore incapable of phototropism. About nine years after Went's discovery English-American plant physiologist Kenneth Vivian Thimann isolated and determined the structure of Indoleacetic Acid (IAA), the only naturally occuring auxin found in plant tissues, which was the same substance that Went had discovered.

Indoleacetic Acid (IAA)
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1H-indole-3-butyric Acid (IBA)
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1-Napthaleneacetic Acid (NAA)

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2,4-Dichlorophenoxy Acetic Acid (2,4-D)
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p-Chlorophenoxyacetic Acid (4-CPA)
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(2,4,5,-Trichlorophenoxy)Aacetic Acid (2,4,5-T)
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3,6-dichloro-2-methoxybenzoic Acid (Dicamba)
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4-amino-3,5,6-trichloropicolinic Acid (Picloram)
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Cytokinins
Write the section on Cytokinins here.

Other Plant Growth Regulators
Write the section on other here.