Indole-3-acetic acid Auxins

All these compounds are intermediates in indole-3-acetic acid (auxin) biosynthesis of plants. They have been prepared on microscale341 with reasonably high yield, high purity... 

Phytohormones are substances that, at low concentration, function to coordinate plant growth and development. The compormds that have been considered as plant hormones include indole-3-acetic acid (auxin), cytokinins, gibberelhns (GA), ethylene and abscisic acid (ABA). In addition, brassinosteroids, jasmonic acid (JA) and saUcyhc acid (SA) have been shown to display important growth regulating activities and are also considered to function as phytohormones. 

Auxins Derivative of tryptophan - e.g. indole acetic acid. Controls H+/K+ balance and growth... 

Arabidopsis thalina, 236-238 Archaebacteria, 272 Auxin, (indole acetic acid, IAA), 218— 223,238... 

Auxin Herbicides Synthetic mimics of natural auxin - Indole -acetic-acid... 

Another important factor of hormone-hormone interaction is the hormonal control of hormonal movement and polarity. Thus, various cytokinins have been reported to increase the polar movement of indole acetic acid and vice versa. Gibberellin treatment was shown also under cer- bain circumstances to increase the basipetal auxin movement. On the other hand, abscisic acid decreases the auxin movement and ethylene, according to some evidence, the gibberellin movement, perhaps through a promotion of conjugation of the auxins with aspartate and of the gibberellins with glucose (cf. Eef. 27). 

At physiological concentrations (10 M), flavonoids may either stimulate or inhibit lAA oxidase (an enzyme which regulates the amount of the plant-growth-regulating hormone indole acetic acid (lAA or auxin) activity in peas... 

Naqvi SM, Gordon SA (1965) Auxin transport in flowering and vegetative shoots of Coleus blumei Benth. Plant Physiol 40 116-118 Naqvi SM, Gordon SA (1966) Auxin transport in Zea mays L. coleoptiles. I. Influence of gravity on the transport of indoleacetic acid-2-Plant Physiol 41 1113-1118 Naqvi SM, Dedolph RR, Gordon SA (1965) Auxin transport and geo tropical potential in corn coleoptile sections. Plant Physiol 40 966-968 Newman IA (1959) Electrical determination of transport of 3-indole acetic acid in Avena. Nature 184 1728-1729... 

Zbell B, Walter-Back C (in press) Signal transduction of auxin on isolated plant cell membranes Indications for a rapid polyphosphoinositide response stimulated by indole acetic acid. 

Indole acetic acid, a biosynthetic product from tryptophan, is one of the most common examples of the group of substances often structiirally unrelated but knovm generally as auxins. They v ere fist observed in fungi in 1954 1933 and it was not imtil 1945 that they were actually found in plants. Auxin inliibits the elongation of roots with a concurrent thickening. Lateral grov th, v/hich is stimulated, does not compensate for the dry matter lost. Lov/ concentrations or brief exposure to auxin can be stimulatory to root grov/th. 

D Phenoxy Synthetic auxins Synthetic auxins. Action like indole acetic acid 1945 Post- emergence Cereals, maize, potato, peanuts, fiuit, noncrop use, sugarcane, rice, citrus, sunflower Broadleaf weeds, 200-2000... 

The mode of action is by inhibiting 5-enolpymvyl-shikimate-3-phosphate synthase. Roundup shuts down the production of the aromatic amino acids phenylalanine, tyrosine, and tryptophane (30). Whereas all these amino acids are essential to the survival of the plant, tryptophane is especially important because it is the progenitor for indole-3-acetic acid, or auxin, which plays an important role in growth and development, and controls cell extension and organogenesis. 

Figure 8.4 Glucosinolate and IAA pathways. IAA indole-3-acetic acid IAN indole-3-acetonitrile IAOx indole-3-acetaldoxime. A loss of function of CYP83B drives the IAOx to IAA and an auxin-overproducing phenotype is the result.

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