Naphthalene 2-acetic acid, auxin

In this context, we recently discovered close correlations between auxin-induced ethylene synthesis, massive accumulations of ABA in root md even more in shoot tissue and inhibition of their growth. This phenomenon, which has been reported for the first time, was demonstrated for auxin herbicides from different chemical classes (Figure 1), such as quinmerac, quinclorac, MCPA, naphthalene acetic acid, dicamba and picloram, and lAA at high concentration, in a variety of dicot species, including members of the Sola-naceae, Umbelliferae, Fabaceae, Scrophulariaceae and Brassicaceae [35, 39, 40]. ABA accumulation and concomitant epinastic effects and reduced shoot growth were also... 

Fig. la. Structures of plant hormones (a) Auxins Indole-3-acetic acid (lAA) Indoleacetonitrile (IAN) Phenylacetic acid (PAA) 2,4-dichlorophenoxyacetic acid (2,4-D) a-naphthalene acetic acid (NAA). 

Of the bicyclic acids, i-naphthaleneacetic acid (NAA, IX) is the best known structural analogue of indoleacetic acid, also resembling the natural auxin in many aspects of its actions. The fact that the isomeric 2-naphthalene-acetic acid (X) is very weakly active only, forms one of the most intriguing questions on structure-activity relationships, especially when compared with the inverse relations found with the naphthoxyacetic acids (c/. Section 4). 

Dichlorophenpxy) acetic acid-14C is metabolized by plant tissue to inactive, water-soluble substances, some of which regenerate the parent acid on hydrolysis. The rate of metabolism differs with different species, but is usually low in comparison with the indole or naphthalene auxins. One of the earlier studies described a single major metabolite in corn, wheat, peas, and tomatoes,121 the identity of which is still uncertain. In another study of differences between species which were susceptible and those which were resistant to the herbicide, the resistant red currant metabolized 50% of the carboxyl-labeled and 20% of the methylene-labeled (2,4 dichlorophenoxy)acetic acid to 14COi in seven days, whereas the susceptible black currant altered122 only 2%. Similar effects were found with apple varieties. Strawberry and lilac decarboxylated the herbicide readily however, 16 other species, of various susceptibilities to herbicide, were unable to decarboxylate the acid to any significant extent. In both varieties of currant, 5 to 10% of the herbicide was converted into water-soluble derivatives of the parent acid, and 10 to 30% was bound in the leaf tissue in an unextractable form. 

Many synthetic auxins have been produced, including 2,4-dichIoro-phenoxyacetic acid or 2,4-D naphthalene-l-acetic acid and 2,3,6-trichlorobenzoic acid, among others. Used as a herbicide. 2.4-D is described in Herbicides. 

Indole-3-acetic acid synthetic auxins including indoles, benzoic acids, naphthalene acids, chloro-phenoxy acids, naphthoxy acid... 

Thus, anthraquinone synthesis in cell suspension cultures of Morinda oitrifolia depends strictly on auxins. However, among 14-6 substances showing auxin activity tested by Zenk et al. (37), only a few were able to trigger anthraquinone metabolism. Naphthalene-1-acetic acid was the most effective one. In contrast, the same cells cultivated in a medium containing 2,4-i) as the only auxin did not produce anthraquinone. 

Figure 7.9 BLM response to auxin receptor, naphthalene 1-acetic acid (NAA), ATP and C6H5COOH in various combinations. (Reprinted by kind permission of Academic Press, Orlando, FI).

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