NITRITE OXIDATION BY NITROBACTER 447 4. The relationship between the rate of oxidation and the partial pressure of dissolved oxygen has been studied at several temperatures. 5. A discussion of the effect of temperature on the parameters of the rate equations for the oxidation of nitrite is presented. This work represents part of an investigation supported by the Institut pour l'Encouragement de la Recherche Scientifique dans l'Industrie et I'Agriculture.
Degradation of indole-3-acetic acid was investigated in etiolated pea shoots; the study was limited to indolic metabolites. The products formed were fractionated by column chromatography and identified by thin-layer chromatography and chemical methods. The pathway of indole-3-acetic acid degradation involving indole-3-aldehyde was found to be more significant than stated in literature, and indole-3-methanol was established as the major indolic metabolite.
Metabolic reactions involving the aliphatic side chain of tryptophan were studied in the holoparasitic dicotyledonous plants Orobanche graciis Sm., 0. haea Baumg., and 0. ramosa L. Unlike known autotrophic plants, the parasite metabolized L-tryptophan directly to indole-3-carboxaldehyde, which was further converted to indole-3-methanol and indole-3-carboxylic acid. Independently, these metabolites were also formed from D-tryptophan, tryptamine, indole-3-lactic acid, and indole-3-acetic acid. As in autotrophic plants, tryptophan and tryptamine were also converted, via indole-3-acetaldehyde, to indole-3-acetic acid, indole-3-ethanol, and its glucoside. free from adhering soil and stored overnight. The plant material was cut into sections about 1 cm in length. Boiled plant material was prepared in flasks immersed in a boiling water bath for 30 min.Incubation Procedure. Substrate solutions (1 ml/g of plant material) were prepared in 0.067 M KH2PO4 (pH 4.5) at approximate concentrations of 1 mg/ml for D-and L-tryptophan, tryptamine hydrochloride, indole-3-lactic acid, and tryptophol, and 0.1 mg/ml for IAA, indole-3-acetaldehyde, indole-3-methanol, indole-3-carboxaldehyde, and indole-3-carboxylic acid. Inhibitors were added to the substrate solutions at 1 to 2 mg/ml for cycloserine and semicarbazide hydrochloride and 0.1 mg/ml for KCN. These solutions were vacuum-infiltrated (at 20 mm Hg) into the plant sections. The sections took up about one-quarter of the solutions, a great deal of which was retained in dead space, such as that in between bracts and in flower buds. Intemal substrate levels per g of metabolically active plant tissue are, thus, smaller than are those per ml of the external solutions by at least one order of magnitude. The plant material and the remaining substrate solutions were incubated separately at 22°C for 5 h, the latter with aeration.Prepurification of Plant Extracts. After incubation, the plant material was homogenized in a 2-fold (w/v) amount of methanol.The homogenate was filtered, and the residue was reextracted. The combined filtrates were stored at -10°C until used. They were then concentrated in vacuo to a few ml; methanol (50 ml) was added, and the mixture was left at -10°C overnight. The precipitate was discarded, and the filtrate was concentrated in vacuo, adjusted to 10 ml with methanol, and extracted, once with 30 ml and a second time with 15 ml of benzene. The combined extracts were evaporated and the residue extracted with 5 x
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...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.