The Bioproduction of Indole-3-Acetic Acid and Related Compounds in Root Nodules and Roots of Lupinus Luteus L. And by Its Rhizobial Symbiont

Abstract

The bioproduction of indole-3-acetic acid (IAA) and indole-3-carboxylic acid (K'A) 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 tissueis 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.

Aromatic aminotransferase activity and indoleacetic acid production in Rhizobium meliloti

“…is a first step in determining whether bacterially produced IAA is involved in nodule development. Biochemical evidence supports the hypothesis that the first step in IAA production by fast-growing rhizobia is likely to be a transamination of Trp to indolepyruvate (3,(10)(11)(12)14). Indole pyruvate could then either undergo spontaneous degradation to IAA or be specifically decarboxylated to indole acetaldehyde and then converted to IAA.…”

Phytohormones, Rhizobium Mutants, and Nodulation in Legumes

“…Several reports indicate that root nodules have greater auxin content than the parent roots in the legumes Pisum sativum (17), Pisum arvense (19), Glycine max (17), and Lupinus luteus (9,16) and in the nonlegume, Alnus glutinosa (10). With the exception of the work of Dullaart (9,10), who used spectro- fluorimetry, these studies have relied on bioassay and need to be confirmed using an unambiguous quantitation method such as mass spectrometry.…”

“…Several reports indicate that root nodules have greater auxin content than the parent roots in the legumes Pisum sativum (17), Pisum arvense (19), Glycine max (17), and Lupinus luteus (9,16) and in the nonlegume, Alnus glutinosa (10). With the exception of the work of Dullaart (9,10), who used spectro- fluorimetry, these studies have relied on bioassay and need to be confirmed using an unambiguous quantitation method such as mass spectrometry. In the work presented here, we Seeds of Pisum sativum L. cultivar Greenfeast were grown as described previously (8), except when nodules were labeled directly, when plants were grown in large upright-placed Petri dishes (13.5 cm diameter) containing 150 ml of sterile solid (1.5% (w/v) agar) modified Fahraeus medium (24).…”

The genetic analysis of Rhizobium in relation to symbiotic nitrogen fixation

“…Rhizobia have been reported to produce small amounts of cytokinins (Phillips and Torrey, 1970) and hence adenine auxotrophs may be unable to produce adequate amounts. However this type of argument does not appear to apply to the production of indole-acetic acid, a tryptophan derivative which is another hormone produced by rhizobia (Dullaart, 1970). All 20 Trp auxotrophs of R. leguminosarum studied by Pain (1979) and one of R. meliloti studied by Dénairé et a!.…”