Indole-3-acetic acid and indole-3-ethanol in light-grown Pisum sativum seedlings and their localization in chloroplast fractions

Brown, Bobby A.; Crozier, Alan; Sandberg, Göran; Jensen, Einar

doi:10.1016/s0031-9422(00)85470-9

Cited by 17 publications

(7 citation statements)

References 15 publications

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“…Although the percent 15N enrichment of IAN is less than expected for a precursor to IAA, the percent isotopic enrichments are so similar that it is difficult to rule out IAN as an intermediate Fig. 1 (3 There is evidence to suggest that tryptophan and IAA are synthesized in plastids (26)(27)(28)(29), and it has been argued (30) that a discrepancy between the heavy isotope enrichments of tryptophan and IAA could be explained if (i) IAA is made only from newly synthesized tryptophan and (ii) there is an unlabeled pool of tryptophan, inaccessible to IAA biosynthesis. We discount this interpretation of our double-labeling experiment for two reasons.…”

Section: Resultsmentioning

confidence: 99%

Arabidopsis thaliana auxotrophs reveal a tryptophan-independent biosynthetic pathway for indole-3-acetic acid.

Normanly

Cohen

Fink

1993

Proc. Natl. Acad. Sci. U.S.A.

248

216

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We used tryptophan auxotrophs of the dicot Arabidopsis thaliana (wall cress) to determine whether tryptophan has the capacity to serve as a precursor to the auxin, indole-3-acetic acid (IAA). Quantitative gas chromatographyselected ion monitoring-mass spectrometry (GC-SIM-MS) The phytohormone auxin plays a central role in plant growth and development as a regulator of numerous biological processes, from cell division, elongation, and differentiation to tropic responses, fruit development, and senescence (1). The biosynthetic route to the synthesis ofthe most abundant plant auxin, indole-3-acetic acid (IAA), has been the subject of controversy for decades. The observation that radiolabeled tryptophan, when applied to watermelon slices, yielded radiolabeled IAA (2) was the first of numerous biochemical studies from which several pathways involving the conversion of tryptophan to IAA have been proposed (Fig. 1). In most of the in vitro studies where radiolabeled tryptophan was converted to IAA, at best only a few percent of the total radioactivity was recovered as IAA. This inefficient conversion of tryptophan to IAA could be accounted for by contaminating epiphytic bacteria (4, 5). Indeed, maize coleoptiles do not convert tryptophan to IAA when incubated in sterile conditions (6). More recently, Baldi et al. (7) showed that feeding tryptophan in high concentration to Lemna gibba (duckweed) increased the pool size of tryptophan but had negligible effects on IAA levels. Additionally, feeding Lemna[15N]tryptophan to the extent that 99% of the tryptophan pool was 15N-labeled did not result in a significant 15N enrichment of IAA. Bandurski et al. (8) showed that maize seedlings grown in the presence of deuterium incorporate label into tryptophan but not IAA. The isolation of tryptophan auxotrophs in both maize and Arabidopsis makes it possible to determine whether tryp-The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.tophan is indeed the precursor to IAA. The orange pericarp (orp) mutant of maize does not make tryptophan due to a defect in tryptophan synthase p activity (9), yet it has 50-fold higher levels of IAA (10). We have used tryptophan auxotrophs of the dicot Arabidopsis thaliana (11-13) to determine whether tryptophan is the sole precursor to IAA. In this study we show that there is a tryptophan-independent IAA biosynthetic pathway. Our data indicate that the precursor is likely to be a compound earlier in the tryptophan biosynthetic pathway, between anthranilate and indole. MATERIALS AND METHODSA. thaliana ecotype Columbia carrying mutations trpl-1, trp2-1, and trp3-1 have been described (11-13). Seeds were surface sterilized (11) MA; 98 atom %) was added to a final concentration of50 ,uM. After 13 days the seedlings were weighed, frozen in liquid nitrogen, and stored at -80°C.Isolation of IAA, Indole-3-acetonitrile (IAN), Indole, and Trypt...

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Section: Resultsmentioning

confidence: 99%

Arabidopsis thaliana auxotrophs reveal a tryptophan-independent biosynthetic pathway for indole-3-acetic acid.

Normanly

Cohen

Fink

1993

Proc. Natl. Acad. Sci. U.S.A.

248

216

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“…In contrast, auxin entering the cell from outside would have access to the active sites. There is, for example, some evidence that the chloroplast is the major site of IAA synthesis (Brown et al 1986). It is interesting in connection with compartmentalisation that we have found that XIIB2 can be rescued "from inside" by transformation with the tms genes of Agrobacterium (data not shown).…”

Section: Discussionmentioning

confidence: 99%

A temperature-sensitive auxin auxotroph not deficient in indole-3-acetic acid

Oetiker

Gebhardt²,

King

1990

Planta

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A temperature-sensitive variant of Hyoscyamus muticus L. expressing a lethal phenotype in both cultured cells and regenerated plants has been shown to be a conditional auxin auxotroph with an absolute requirement for an exogenous auxin at temperatures above 30° C but not at lower temperatures. The requirement was satisfied by indole-3-acetic acid (IAA) and all active auxin analogous tested. Despite this dependence on exogenous auxin at high temperatures, the variant nevertheless synthesises IAA under these conditions and contains a pool of free IAA equal to that of the wild type. Furthermore, there is no depletion of the cellular IAA pool on incubation at high temperature in the absence of added auxin, even during the expression of the auxin-auxotrophic phenotype. The characteristics of this variant indicate that auxin auxotrophy can be lethal at the plant level and raises questions about the cellular function and mode of action of auxin.

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“…This is supported by the fact that 2,4-D increases endogenous IAA accumulation (19), and 2,4-D has also been shown to increase the level of auxin-binding proteins in the membranes of carrot cells (15). It has been suggested that tryptophan (5,14) and perhaps IAA (7,17,27) Although the conversion of tryptophan into IAA has been demonstrated many times in bacteria (23) and plants (30), the role of tryptophan as the obligatory precursor of IAA has now been seriously questioned (3,32). The enzymes thought to be involved in the conversion of tryptophan into IAA have not been shown to be specific, leaving open the possibility that such a conversion would not be a controlling factor in normal IAA biosynthesis (10).…”

Section: H20 Labeling In Embryogenic Suspension Culturesmentioning

confidence: 99%

“…[13C6]IAA as the internal standard, as previously described (8,9 7. The IAA in the extracts from cultures grown on the medium containing deuterated water was purified, and 2H incorporation was determined as described above.…”

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confidence: 99%

Regulation of Indole-3-Acetic Acid Biosynthetic Pathways in Carrot Cell Cultures

Michalczuk¹,

Ribnicky²,

Cooke³

et al. 1992

Plant Physiol.

175

102

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Indole-3-acetic acid and indole-3-ethanol in light-grown Pisum sativum seedlings and their localization in chloroplast fractions

Cited by 17 publications

References 15 publications

Arabidopsis thaliana auxotrophs reveal a tryptophan-independent biosynthetic pathway for indole-3-acetic acid.

Arabidopsis thaliana auxotrophs reveal a tryptophan-independent biosynthetic pathway for indole-3-acetic acid.

A temperature-sensitive auxin auxotroph not deficient in indole-3-acetic acid

Regulation of Indole-3-Acetic Acid Biosynthetic Pathways in Carrot Cell Cultures

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