Metabolism of Tryptophan, Indole-3-acetic Acid, and Related Compounds in Parasitic Plants from the Genus Orobanche

Abstract

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

Nutrimetabolomics fingerprinting to identify biomarkers of bread exposure in a free-living population from the PREDIMED study cohort

“…In this context, 3-ICA has been described as an end metabolite synthesized from conversions of tryptophan to indole-3-carboxaldehyde (Magnus et al 1982). However, this amino acid has also been detected in whole-grain bread (Jiang and Peterson 2013).…”

Metabolism of Tryptophol in Higher and Lower Plants

“…The following compounds which might have been expected to participate in tryptophol metabolism, and which should mostly be detectable by the methods used (13,15) were absent in at least 80% of the species examined:…”

“…More IAA was isolated from Pseudomonas than from most plant species. However, the pure bacterial cultures contained I03 to I04 times more bacteria than are usually found as contaminants in metabolic experiments with plant sections (13,15). It (16).…”

“…A previously described method was used (10,(13)(14)(15). Briefly, organic solvent-insoluble constituents in the plant extracts were precipitated with methanol and benzene:methanol (5:1, v/v).…”

Identification and Quantification of Indole-3-methanol in Etiolated Seedlings of Scots Pine (Pinus sylvestris L.)

“…In vivo incubations of IAA with segments of Pisum sativum (7,13), Orobanche sp. (14), and Phaseolus vulgaris (7) also yielded IM as one of the catabolic products. Indirect evidence for an IM pathway in plants comes from the identification of BIM, a proposed degradation product of IM, as a product of IAA catabolism in both a crude enzyme extract from Zea mays (3) and HRP (24).…”