Metabolism of Tryptophol in Higher and Lower Plants

Abstract

Bacteria, thallophytes, and seed plants (107 species), supplied with exogenous indole-3-ethanol (tryptophol), formed one or more of the following metabolites: O-acetyl tryptophoL an unknown tryptophol ester (or a set of structurally closely related esters), tryptophol glucoside, tryptophol plactoside, indole-3-acetic acid (IAA), and indole-3-carboxylic acid. The unknown ester was formed by all species exAmined; 0-acetyl tryptophol appeared sporadically in representatives of most major taxonomic groups. Tryptophol galactoside was found in the algae Chlorella, Euglena, and Ochromoaas. The glucoside was formed by many eucaryotic plants, but not by bacteria; it was a significant tryptophol metabolite in vascular plants. IAA, if detectable at all, was usually a minor metabolite, as should be expected, if tryptophol oxidase responds to feedback inhibition by IAA. Indole-3-carboxylic acid, formed by a few fungi and mosses, was the only tryptophol metabolite detected which is likely to be formed via IAA.Indole-3-ethanol (tryptophol2) has been established as an endogenous plant constituent (6,19,23). It is also formed in vitro by preparations from bacteria, thallophytes, and seed plants from compounds supposed to participate in the biogenesis of IAA (e.g. 18,23). In fact, tryptophol appears to be in an oxidase-reductasemediated equilibrium with the IAA precursor, indole-3-acetaldehyde (5, 16). The oxidase has been isolated and found to be feedback inhibited by IAA (16). This points to the involvement of tryptophol in a mechanism stabilizing auxin levels in plants. Its in vivo significance has, however, remained unclear, because IAA concentrations necessary to inhibit the isolated tryptophol oxidase are larger than bulk concentrations of the hormone in plant tissues (16).Local IAA concentrations at points ofregulation may be higher than bulk concentrations. Also, removal of tryptophol oxidase from its natural subcellular environment may render the enzyme less sensitive to feedback inhibitors. For these reasons, we were looking for indications of regulated IAA formation from tryptophol in systems containing nondisrupted cell structures. Suspensions of unicellular plants and sections of multicellular plants were supplied with a large excess of tryptophol. In the absence of regulatory mechanisms, this might reasonably be expected to lead to drastically enhanced IAA levels. However, the majority of plants examined did not accumulate substantial amounts of 2 Abbreviations: tryptophol, indole-3-ethanol or 3-(2-hydroxyethyl)indole; Ve, elution volume.The most abundant tryptophol metabolites in bacteria, thallophytes, and seed plants were conjugates: esters and glycosides.MATERIALS AND METHODS Instrumentation. 'H NMR spectra were recorded at 100 MHz on a JEOL FX-100 Fourier-transform spectrometer. Chemical shifts (a) were recorded relative to tetramethylsilane. GC-MS was on a Hewlett-Packard 5985a instrument, using helium at 30 ml/ min as the carrier gas and electron impact ionization at 70 ev. Columns and temperature pr...

Free radical–scavenging activity and DNA damaging potential of auxins IAA and 2‐methyl‐IAA evaluated in human neutrophils by the alkaline comet assay

“…A recent article on tryptophol [27], which is a natural compound involved in the metabolism of IAA in higher plants [34], reports an in vitro genotoxic effect of tryptophol on lymphocytes in a manner similar to that observed herein for IAA and 2-Me-IAA. This means that the level of DNA damage was not directly related to the applied concentration; the lowest and the highest concentrations of the examined indoles did not induce the corresponding level of damages.…”

Assessment of Tryptophol Genotoxicity in Four Cell Lines In Vitro: A Pilot Study with Alkaline Comet Assay

“…Cells were treated with tryptophol in the Figure 1 Structural formula of tryptophol bacteria, yeasts, and fungi (7,(12)(13)(14). In higher plants, tryptophol is an endogenous constituent and growth regulator (15). It is also a product of tryptophan metabolism by Trypanosoma brucei and is involved in the pathophysiology of sleeping sickness caused by these blood parasites (16,17).…”

Salkowski’s Reagent Test as a Primary Screening Index for Functionalities of Rhizobacteria Isolated from Wild Dipterocarp Saplings Growing Naturally on Medium-Strongly Acidic Tropical Peat Soil

“…TOL is known to be derived from endogenous IAA by plants, and it is immediately converted to O-acetyl tryptophol, which is stocked in plant tissues. 28) TOL is also known as an antimicrobial substance and a weak auxin agonist, 29) and it has been identified as an apoptosis-inducing factor in a human leukemic cell line. 30) Hence, it might be necessary to investigate the association of TOL with plant apoptosis.…”

“…An MW solution supplemented with 100 mg l À1 TRP was adjusted to pH 4.0, 5.0, 6.0, 7.0, and 8.0 using 2 M H 2 SO 4 . To 100 ml of the TRP-amended medium, a loop of bacteria was inoculated and standing-cultured for 7 d in the dark at 28 C. The process of extracting TRP metabolites was as described above.…”