Indole-3-acetic acid

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Indole-3-acetic acid
Indol-3-ylacetic acid.svg
IUPAC name
2-(1H-indol-3-yl)acetic acid
Other names
Indole-3-acetic acid,
indolylacetic acid,
1H-Indole-3-acetic acid,
indoleacetic acid,
87-51-4 YesY
ChEBI CHEBI:16411 YesY
ChemSpider 780 YesY
DrugBank DB07950 YesY
Jmol-3D images Image
KEGG C00954 YesY
PubChem 802
Molar mass 175.18 g·mol−1
Appearance White solid
Melting point 168 °C (334 °F; 441 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 YesY verify (what isYesY/N?)
Infobox references

Indole-3-acetic acid (IAA) is the most common, naturally-occurring, plant hormone of the auxin class. It is the best known of the auxins, and has been the subject of extensive studies by plant physiologists.[1] Chemically, IAA is a carboxylic acid in which the carboxyl group is attached through a methylene group to the C-3 position of an indole ring. In appearance, IAA is a colorless solid.

Biosynthesis and biological activity[edit]

Main article: Auxin

IAA is predominantly produced in cells of the apex (bud) and very young leaves of a plant. Plants can synthesize IAA by several independent biosynthetic pathways. Four of them start from tryptophan, but there is also a biosynthetic pathway independent of tryptophan.[2] Plants mainly produce IAA from tryptophan through indole-3-pyruvic acid.[3][4] IAA is also produced from tryptophan through indole-3-acetaldoxime in Arabidopsis thaliana.[5]

IAA has many different effects, as all auxins do, such as inducing cell elongation and cell division with all subsequent results for plant growth and development. On a larger scale, IAA serves as signaling molecule necessary for development of plant organs and coordination of growth.

It is formed from tryptophan, along with tryptophol in rats infected by Trypanosoma brucei gambiense.[6]

Synthetic analogs[edit]

There are less expensive and metabolically stable synthetic auxin analogs on the market for use in horticulture, such as indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA).[citation needed]

Studies of IAA in the 1940s led to the development of the phenoxy herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Like IBA and NAA, 2,4-D and 2,4,5-T are metabolically and environmentally more stable analogs of IAA. However, when sprayed on broad-leaf dicot plants, they induce rapid, uncontrolled growth, eventually killing them. First introduced in 1946, these herbicides were in widespread use in agriculture by the middle of the 1950s.[citation needed]


Chemically, it can be synthesized by the reaction of indole with glycolic acid in the presence of base at 250 °C:[7]

Synthesis of indole-3-acetic acid.png

Alternatively the compound has been synthesized by Fischer indole synthesis using Glutamic acid and Phenylhydrazine.[8] Glutamic acid was converted to the necessary aldehyde via Strecker degradation.

Many methods for its synthesis have been developed since its original synthesis from indole-3-acetonitrile.[9]

Gene Regulation[edit]

IAA enters the cell nucleus and binds to a protein complex composed of a Ubiquitin-activating enzyme (E1), a Ubiquitin-conjugating enzyme (E2), and a Ubiquitin ligase (E3), resulting in Ubiquitination of Aux/IAA proteins with increased speed.[10] Aux/IAA proteins bind to auxin response factor (ARF) proteins, forming a heterodimer, suppressing ARF activity. [11] ARF's bind to auxin-response gene elements in promoters of auxin regulated genes, generally activating transcription of that gene when an Aux/IAA protein is not bound.[12]

Toxicity on human organs[edit]

Little research has been conducted on the effects of IAA on humans and toxicity data is limited. No data on carcinogenic, teratogenic, or developmental effects have been created. IAA is listed in its MSDS as potentially mutagenic to mammalian somatic cells. It is listed as a potential skin, eye, and respiratory irritant, and users are warned not to ingest it. Protocols for ingestion, inhalation, and skin/eye exposure are standard for moderately poisonous compounds and include thorough rinsing in the case of skin and eyes, fresh air in the case of inhalation, and immediately contacting a physician in all cases to determine the best course of action. Do not induce vomiting in the case of ingestion nor attempt to give anything by mouth to an unconscious person. The NFPA 704 health hazard rating for IAA is 2, which denotes a risk of temporary incapacitation with intense or prolonged, but not chronic exposure, and a possibility of residual injury.[13]

Other uses[edit]

Effects on embryonic rat brain development[edit]

Studies have been performed to determine the effects IAA and similar chemicals on the development of the cerebral cortex during early embryogenesis. One study performed in rats determined that such compounds decreased the locomotor activities of the embryos/fetuses. Further, treatment with IAA and analog 1(methyl)-IAA resulted in significantly decreased brain sizes (relative to body weight) in embryonic day 21 animals.[14]


IAA and horseradish peroxidase (HRP) have been proposed on the basis of polymer transfer and gene-direction, they may be useful in cancer therapy. Radical-IAA IAA in the human body will attach to cells with that characterized by HRP. By this means the HRP reaction cells can be selectively killed. But because of the competitive bonding of the IAA-HRP more studies must be done before clinical studies can begin.[15]


  1. ^ Simon, Sibu; Petrášek, Jan (2011). "Why plants need more than one type of auxin". Plant Science 180 (3): 454–60. doi:10.1016/j.plantsci.2010.12.007. PMID 21421392. 
  2. ^ Zhao, Yunde (2010). "Auxin Biosynthesis and Its Role in Plant Development". Annual Review of Plant Biology 61: 49–64. doi:10.1146/annurev-arplant-042809-112308. PMC 3070418. PMID 20192736. 
  3. ^ Mashiguchi, Kiyoshi; Tanaka, Keita; Sakai, Tatsuya; Sugawara, Satoko; Kawaide, Hiroshi; Natsume, Masahiro; Hanada, Atsushi; Yaeno, Takashi et al. (2011). "The main auxin biosynthesis pathway in Arabidopsis". Proceedings of the National Academy of Sciences 108 (45): 18512–7. Bibcode:2011PNAS..10818512M. doi:10.1073/pnas.1108434108. PMC 3215075. PMID 22025724. 
  4. ^ Won, Christina; Shen, Xiangling; Mashiguchi, Kiyoshi; Zheng, Zuyu; Dai, Xinhua; Cheng, Youfa; Kasahara, Hiroyuki; Kamiya, Yuji et al. (2011). "Conversion of tryptophan to indole-3-acetic acid by TRYPTOPHAN AMINOTRANSFERASES OF ARABIDOPSIS and YUCCAs in Arabidopsis". Proceedings of the National Academy of Sciences 108 (45): 18518–23. Bibcode:2011PNAS..10818518W. doi:10.1073/pnas.1108436108. PMC 3215067. PMID 22025721. 
  5. ^ Sugawara, Satoko; Hishiyama, Shojiro; Jikumaru, Yusuke; Hanada, Atsushi; Nishimura, Takeshi; Koshiba, Tomokazu; Zhao, Yunde; Kamiya, Yuji; Kasahara, Hiroyuki (2009). "Biochemical analyses of indole-3-acetaldoxime-dependent auxin biosynthesis in Arabidopsis". Proceedings of the National Academy of Sciences 106 (13): 5430–5. Bibcode:2009PNAS..106.5430S. doi:10.1073/pnas.0811226106. JSTOR 40455212. PMC 2664063. PMID 19279202. 
  6. ^ Short-Term Metabolism of [14C]Tryptophan in Rats Infected with Trypanosoma brucei gambiense. Henry Howard Stibbs and John Richard Seed, J Infect Dis., 1975, volume 131, issue 4, pages 459-462, doi:10.1093/infdis/131.4.459
  7. ^ Johnson, Herbert E.; Crosby, Donald G. (1964). "Indole-3-acetic Acid". Org. Synth. 44: 64. ; Coll. Vol. 5, p. 654 
  8. ^ Fox, Sidney W.; Bullock, Milon W. (1951). "Synthesis of Indoleacetic Acid from Glutamic Acid and a Proposed Mechanism for the Conversion". Journal of the American Chemical Society 73 (6): 2754–2755. doi:10.1021/ja01150a094. 
  9. ^ Majima, Rikō; Hoshino, Toshio (1925). "Synthetische Versuche in der Indol-Gruppe, VI.: Eine neue Synthese von β-Indolyl-alkylaminen". Berichte der deutschen chemischen Gesellschaft (A and B Series) 58 (9): 2042–6. doi:10.1002/cber.19250580917. 
  10. ^ Pekker, MD; Deshaies, RJ (2005). "Function and regulation of cullin-RING ubiquitin ligases.". Plant Cell. (6): 9–20. 
  11. ^ Tiwari, SB; Hagen, G; Guilfoyle, TJ (2004). "Aux/IAA proteins contain a potent transcriptional repression domain.". Plant Cell. (16): 533–43. 
  12. ^ Ulmasov, T; Hagen, G; Guilfoyle, TJ (1997). "ARF1, a transcription factor that binds to auxin response elements.". Science (276): 1865–68. 
  13. ^ "Indole-3-Acetic Acid: Material Safety Data Sheet." November 2008.
  14. ^ Furukawa, Satoshi; Usuda, Koji; Abe, Masayoshi; Ogawa, Izumi (2005). "Effect of Indole-3-Acetic Acid Derivatives on Neuroepithelium in Rat Embryos". The Journal of Toxicological Sciences 30 (3): 165–74. doi:10.2131/jts.30.165. PMID 16141651. 
  15. ^ Kawano, T (2003). "Possible use of indole-3-acetic acid and its antagonist tryptophan betaine in controlled killing of horseradish peroxidase-labeled human cells". Medical Hypotheses 60 (5): 664–6. doi:10.1016/S0306-9877(03)00012-4. PMID 12710900.