Metabolism of indole-3-acetic acid and natural occurrence of dioxindole-3-acetic acid derivatives in Vicia roots.

Three indole-3-acetic acid (IAA) metabolites [compounds A and B and indole-3-acetylaspartic acid (IAAsp) ] accumulated in Vicia faba roots when (14)C-IAA was applied to the cotyledon. IAAsp formation was increased by the application of a high concentration (2.5 × 10(-4) m) of IAA, while the accumulation of compound A was more conspicuous in the roots when a lower concentration (3.3 × 10(-5) m) of IAA had been applied. This indicates that compound A is not a detoxication product induced by an abnormally high concentration of IAA. Compounds A and B were identified as dioxindole-3-acetic acid derivatives by the UV spectra and their yielding 2-quinolone-4-carboxylic acid upon hydrolysis. Compound A was found to exist in Vicia roots not treated with exogenous IAA, and its naturally occurring content was estimated to be 1 μmole kg(-1) fresh weight. The amount of native compound B was far less than that of compound A.