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

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Abstract
Metabolic reactions involving the aliphatic side chain of tryptophan were studied in the holoparasitic dicotyledonous plants O. gracilis Sm., O. lutea Baumg., and O. ramosa L. Unlike autotrophic plants, the parasite metabolized L-tryptophan directly to indole-3-carboxaldehyde, which was converted to indole-3-methanol and indole-3-carboxylic acid. Independently, these metabolites were formed from D-trytophan, tryptamine, indole-3-lactic acid and IAA. As in autotrophic plants, tryptophan and tryptamine were converted, via indole-3-acetaldehyde, to IAA, indole-3-ethanol and its glucoside. The branch of tryptophan metabolism relevant to auxin biogenesis and catabolism is not rudimentary in Orobanche but even more complex than in autotrophic higher plants.