Tryptophan auxin

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. 

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

Indole-3-acetaldoxime (30) and 4-hydroxyphenylacetaldoxime were shown to be metabolized by plant and pest fungi to 32 and to other related indole- and 4-hydroxyphenyl carboxylic acids, however, the biochemical transformation differed between the two fungi. These biochemical transformations may be relevant to the ability of certain fungi to cause plant diseases . Compound 30 has been shown to be a key intermediate in the biosynthesis of camalexin, 3-thiazolyl-2 -yl-indole, a member of the family of phytoalexins that are produced in response to pathogen attack. It was demonstrated that CYP71A13 catalyzes the conversion of 30 to indole-3-acetonitrile, which is essential for the biosynthesis of camalexin. Thus, the literature supplies a large body of evidence for the existence of a set of enzymes dedicated to the production of the auxin, 32, from tryptophan via indole-3-acetaldoxime (30). 

Aromatic Amino Acid Biosynthesis. The shikimate pathway is the biosynthetic route to the aromatic amino acids tryptophan, tyrosine and phenylalanine as well as a large number of secondary metabolites such as flavonoids, anthocyanins, auxins and alkaloids. One enzyme in this pathway is 5-enolpyruvyl shikimate-3-phosphate synthase (EPSP synthase) (Figure 2.9). 

Phenylalanine, tyrosine, and tryptophan are converted to a variety of important compounds in plants. The rigid polymer lignin, derived from phenylalanine and tyrosine, is second only to cellulose in abundance in plant tissues. The structure of the lignin polymer is complex and not well understood. Tryptophan is also the precursor of the plant growth hormone indole-3-acetate, or auxin (Fig. 22-28a), which has been implicated in the regulation of a wide range of biological processes in plants. 

The shikimate/arogenate pathway leads to the formation of three aromatic amino acids L-phenylalanine, L-tyrosine, and L-tryptophane. This amino acids are precursors of certain homones (auxins) and of several secondary compounds, including phenolics [6,7]. One shikimate/arogenate is thought to be located in chloroplasts in which the aromatic amino acids are produced mainly for protein biosynthesis, whereas the second is probably membrane associated in the cytosol, in which L-phenylalanine is also produced for the formation of the phenylpropanoids [7]. Once L-phenylalanine has been synthesized, the pathway called phenylalanine/hydroxycinnamate begins, this being defined as "general phenylpropanoid metabolism" [7]. 

The effects of auxin upon the growth of plants were truly remarkable. As a result of the concerted effort and interest that plant scientists devoted to this highly fashionable and exciting field of research, much of what we know of the control of plant growth and development by auxin was discovered in these highly productive years. The hormone was derived from the aromatic amino acid tryptophan and was relatively abundant in the rapidly growing meristematic parts of plants such as apical buds and root tips. Inactive bound forms existed, as in seeds, where hydroly-... 

Sarwar, M., Frankenberger, Jr., W.T Influence of L-tryptophan and auxins applied to the rhizosphere on the vegetative growth of Zea mays L. Plant Soil 1994 160 97-104. 

GODDIJN, O.J.M., DE KAM, R.J., ZANETTI, A., SCHILPEROORT, R.A., HOGE, J.H.C., Auxin rapidly down-regulates transcription of the tryptophan decarboxylase gene from Catharanthus roseus. Plant Mol. Biol., 1992, 18, 1113-1120. 

FIGURE 9-27 Metabolites produced in Agrobacterium-mierAeA plant cells. Auxins and cytokinins are plant growth hormones. The most common auxin, indoleacetate, is derived from tryptophan. Cytokinins... 

Finally, tryptophan is used for the synthesis of indole-3-aeetic acid (see here), a plant hormone also known as auxin. 

Of the auxins, the tryptophan metabolite indole-3-acetic acid is the most active. 

Auxin. The imporfant plant hormone indole-3-acetic acid (lAA often called by the more general name auxin) is partially derived by oxidative decarboxylation (Fig. 25-12, top) catalyzed by tryptophan-2-... 

Thus, the manner in which auxins were discovered led to confusion as to the site and mechanism of auxin synthesis. Was the hormone synthesized in the tip by some completely de novo route from simple non-aromatic precursors, or was it stored in the tip in an aromatic form such as tryptophan, or a related indolic compound that could readily be converted to lAA Alternatively, was an aromatic precursor transported from the seed to the tip of the seedling as it grew This latter possibility was suggested by Skoog [12], who called the upward transported form the seed auxin precursor , which he believed to be tryptamine. 

The formation of root nodules associated with nitrogen fixation in legumes is an area of active study. Hormonal involvement in the developmental modifications needed to establish the nodule, has been reviewed [186]. Studies on the molecular characterization of nodulation have shown that early nodulation genes are induced by auxin transport inhibitors, and inhibitor treated roots produce pseudonodules [187]. Rhizobium species appear to produce lAA by a pathway involving the conversion of tryptophan to indole-... 

Standard microbial methods for investigating tryptophan biosynthesis were applied to plants in order to study auxin biosynthesis [6,212,218]. A series of Arabidopsis mutants with lesions in four sites in the pathway from chorismate to tryptophan has been obtained, but so far no comparable array of mutations exists for any other plant species [18]. Normanly et al. [44] used these Arabidopsis mutants to dissect lAA biosynthesis and showed that the non-tryptophan pathway to lAA branches from tryptophan biosynthesis at the point of indole or indole-3-glycerol phosphate. 

Skoog (1940) indicated the relationship between the zinc content and the auxin content in higher plants, while Tsui (1948) concluded that zinc is essential for the biosynthesis of tryptophan in tomatoes. Schiitte (1964) showed the primary role of zinc as a catalyst. Prask and Plocke (1971) found that ribosomes in the cytoplasm of Euglena gracilis normally contain considerable amounts of zinc, and that these organelles become extremely unstable when there is a deficiency of zinc. Confirmation that zinc is necessary for the stability of these ribosomes would also be proof that it is essential for normal growth and development (Price et al. 1972). 

Higher plant studies of tryptophan metabolism have focused on its role as a precursor for indole alkaloids or as a precursor of the auxin indoleacetic acid. The conversion of tryptophan to indoleacetate has been the subject of many investigations for many years. There is considerable uncertainty over the route of degradation. The following diagram presents the possible pathways which have been suggested most frequently ... 

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