Production and metabolism of indole acetic acid in roots and root nodules of Phaseolus mungo

The mature root nodules of Phaseolus mungo (L.), a leguminous pulse, contain higher amount of indole acetic acid (IAA) than non-nodulated roots. The tryptophan pool present in the mature nodule and young roots might serve as a precursor for the IAA production. Presence of IAA metabotising enzymes - IAA oxidase and peroxidase indicate the metabolism of IAA in the nodules and roots. In culture, the symbiont, isolated from the nodules, produced a high amount of IAA, when tryptophan was supplied in the medium as a precursor. The symbiont preferred L-isomer over the DL-or D-isomer of tryptophan for IAA production. The important physiological implication of the IAA production in the legume-Rhizobium symbiosis is discussed. (c) 2006 Elsevier GmbH. All rights reserved.