The bioproduction of indole-3-acetic acid and related compounds in root nodules and roots of Lupinus luteus L. and by its rhizobial symbiont

The bioproduction of indoIe-3-acetic acid (IAA) and indole-3-carboxylic acid (ICA) from L-tryptophan in root nodules and roots of Lupinus luteus and by the symbiotic Rhizobium lupini was studied in vitro. and IAA degradation and the conversion of a number of related indole derivatives were also investigated. The results permit the conclusion that at least a substantial part of the large amounts of IAA present in the root nodules is produced via plant enzymes as a result of a metabolic alteration induced by the rhizobial infection. Young roots appeared to possess a high activity of IAA production from L-tryptophan, but most of this production is masked by enzymatic degradation of IAA. According to the results of the IAA destruction experiments, cell-free enzyme extracts of mature roots show the lowest activity, and the non-dialyzed young root enzyme extract exhibits significantly greater activity than the dialyzed preparations. For the root nodule enzyme preparations this situation was found to be reversed, suggesting that the balance between promoting and inhibiting substances influencing enzymatic IAA degradation in nodule tissue is changed in favour of inhibition as a result of the rhizobial infection. Some interesting data concerning differences in IAA destruction behaviour between different strains of Rh. lupini were also obtained. The results of the comparative investigations concerning the conversion of a number of related indole derivatives indicated that there are some significant differences with respect to the conversion capacities of the different incubation systems.