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On the plant growth hormone produced by Rhizopus suinus

Thimann, Kenneth V. (1935) On the plant growth hormone produced by Rhizopus suinus. Journal of Biological Chemistry, 109 (1). pp. 279-291. ISSN 0021-9258.

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Since it was first discovered that cell elongation in the Avena coleoptile is controlled by a hormone, our understanding of the nature and rôle of this substance has progressed considerably. Apart from the elucidation of its functions in promoting growth, tropisms, and other reactions of the plant, the chemical nature of the substance has been extensively studied. The active substance produced by cultures of the mold Rhizopus suinus was shown by Nielsen (1930) to be ether-soluble, and by Dolk and Thimann (1932) to be an unsaturated organic acid, decomposed by strong acids but not by alkalies, and readily inactivated by oxidation. Its dissociation constant, as measured by Dolk and Thimann, is 10^-4.75. Previously, Went (1928) had shown the molecular weight of the active substance in Avena coleoptiles to be about 376. The active substance in human urine was isolated by Kögl and Haagen-Smit (1931) and by Kögl, Haagen-Smit, and Erxleben (1933), and shown to be an acid, C17H28O(OH)COOH (auxin A), whose lactone is also active, while from malt these workers later isolated (1933) a ketohydroxy acid, C17H28O(OH)COOH (auxin B), which had the same activity per unit weight. On account of the rather small amount of substance available from Rhizopus cultures, and also since the bulk of the partially purified product was lost through spontaneous inactivation (see section, “Concluding stages”), the chemical investigation of the active substance, begun earlier, was dropped. However, the many experiments on purification which had meanwhile been carried out showed that the active substance from Rhizopus did not behave in quite the same way as that from urine. Recently, however, it was shown by Kögl, Erxleben, and Haagen-Smit (1934) that there is in urine a second active substance, identical with β-indolylacetic acid, and Kögl and Kostermans (1934) showed that the molecular weight of the substance produced by Aspergillus and by Rhizopus is that of β-indolylacetic acid rather than that of the C18 compounds. Since preparations from Rhixopus have been extensively used for physiological work, both in this laboratory and elsewhere, the exact nature of the active substance is of considerable interest. The present paper will give evidence that the active substance produced by Rhizopus suinus is in fact β-indolylacetic acid. Identification by the preparation of derivatives and by mixed melting points with the pure synthetic substance was not possible on account of the small amount of material available. Nevertheless, the evidence given below is fairly conclusive. The method of purification, since it differs to some extent from that adopted by Kögl and his coworkers, will also be outlined. Finally, it will be shown that some of the peculiar conditions previously found to be necessary for the production of this growth substance (Thimann and Dolk, 1933) find a simple explanation on this basis.

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Additional Information:Copyright © 1935 by the American Society for Biochemistry and Molecular Biology. (Received for publication, January 17, 1935)
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ID Code:10372
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Deposited On:01 May 2008
Last Modified:03 Oct 2019 00:09

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