Auxin activity

Indolebutyric acid org chem C12H13O2N A crystalline acid similar to indoleacetic acid in auxin activity. Abbreviated IBA. in,dol-byu tir-ik as-od indoxyl orgchem (C8H6N)0H A yellow crystalline glycoside, used as an intermediate in the manufacture of indigo. in dak-sol ... 

Table III Auxin-activity of phenoxypropionic acids (pC5p)...

It is now generally accepted that auxin and low-pH-induced stimulation of elongation growth results from a temporary weakening or relaxation of the wall.400,469,470,473-477 There is some evidence that such hormones as auxin activate, within the cell membrane, ion pumps that lower the pH of the wall,400,468,477,478-481 and it was suggested that the direct... 

The auxin activities of the above phytohormones as well as their silatranylmethyl esters are listed in Tables 26—28. 

Silatranylmethyl ester has a higher auxin activity with respect to the culture of soya tissue than free 2-methylphenoxyacetic acid. At the same time, it has a low activity with respect to tobacco and potato cultures. 1-Silatranylesterof 4-chlorophenoxyacetic... 

These compounds are inhibitors of lipid biosynthesis and auxin activity. 

The main conclusions to be drawn from these investigations are that d(-I-) propionic acids have a stronger auxin activity than the corresponding acetic acids, while l(-) propionic acids have a marked antiauxin action. 

An ortho substituted methoxy group reduces auxin activity, but does not cancel it in compounds of otherwise strong activity. The meta methoxy group strengthens the auxin action in phenoxyacetic acids, but causes decreased activity in otherwise strongly active compounds. The para methoxy group enhances activity in phenoxyacetic acids, but reduces it in phenoxypropionic acids. 

D, 2,4-DP, 2,4,5-T and 2,4,5-TP, applying them alone and simultaneously with the parent acid. Of the 21 acid amides investigated 13 exhibited an antiauxin action, antagonising the auxin activity of the respective phenoxyalcanoic acid. At the same time, the compounds also had their own auxin action, showing on the one hand that amides too have an auxin action, and on the other hand that they are metabolised in plants by the enzymatic pathway to the respective acids and are thus the precursors of the acids. 

Thuillier et at, Compt. Rend. 249, 2081 (1959) Thuillier, Rumpf, Bull. Soc. Chim. France 1960, 1786, Pharmacology Petkov, CA. 65, 20717g (1966) Liberman, Farma-kol. Toksikoi 30, 409 (1967). Auxin activity Conti, Boll. Chim. Farm. 107, 325 (1968). 

The major natural auxin is indole-3-acetic acid (lAA) [42]. A number of related compounds exist in plants, including indolebutyric acid and indoleacetonitrile (Fig. la). These related compounds are active primarily when first converted to lAA [42]. In addition, there are a series of LAA conjugates with sugars and amino acids [43]. Some of these may be detoxification products, but others may be reservoirs of releasable lAA, especially in seeds. Phenylacetic acid (Fig. la) has auxin activity, and exists in sizable amounts in a few plants such as tobacco [42], but it is unclear that this compound actually moves from one part of a plant to another. In addition to the natural auxins, a whole host of synthetic auxins are known. The most widely used are a-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D) (Fig. la). 

There are three major classes of synthetic auxins the aryl acetic acids, which include indoleacetic acid (lAA) itself (Fig. 1 structure 2-1) and 1-naphthyl acetic acid (2-4), phenoxy acetic acids, represented by 2,4-dichlorophenoxy acetic acid (2,4-D) (2-7) and the benzoic acids, e.g. 2,3,6-trichloro benzoic acid (2-9). It remains the case however, that there is no stmcture-activity proposal which satisfactorily covers all molecules which are known to have auxin activity. As is well known, auxins have multiple effects, including promotion of cell elongation, cell division and gene expression. There may well be different receptors for each effect, and differences between receptors. An auxin binding protein (ABP), has now been characterised, and is possibly a receptor controlling cell elongation [3]. 

Anti-auxins are molecules which posses very little auxin activity at best, but which can affect the hormonal mechanism in some way. It appears that steric factors are involved. 

One type of anti-auxin activity may arise when molecules impinge on the f area of the receptor map in Fig. 2. 7-Chloro substitution of lAA can give rise to anti-auxin activity. Dichloroindole isobutyric acid (2-8) is a potent anti-auxin. 2-Naphthyl acetic acid and... 

Although indole-3-acetic acid was the first auxin isolated, and is considered to be the major plant auxin, other compounds with auxin activity also occur in plants. Most of these compounds are active only at higher concentrations than lAA and their role in growth remains largely unknown. Two indolic auxins other than lAA have been isolated from plants, indole-3-butyric acid (IBA) and 4-chloro-indole-3-acetic acid (4-Cl-IAA). 

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