Abstract
Analysis of neutral and acidic ethyl acetate extracts from culture medium of
Azospirillum brasilense
703Ebc by high-performance liquid chromatography (HPLC) and combined gas chromatography-mass spectrometry demonstrated the presence of indole-3-acetic acid (IAA), indole-3-ethanol, indole-3-methanol, and indole-3-lactic acid. IAA in media of 20 strains of
A. brasilense
and
Azospirillum lipoferum
was analyzed quantitatively by both the colorimetric Salkowski assay and HPLC-based isotopic dilution procedures. There was little correlation between the estimates obtained with the two procedures. For instance, the Salkowski assay suggested that the culture medium from
A. brasilense
703Ebc contained 26.1 μg of IAA ml
−1
, whereas HPLC revealed the presence of only 0.5 μg of IAA ml
−1
. Equivalent estimates with
A. brasilense
204Ed were 10.5 and 0.01 μg of IAA ml
−1
, respectively. The data demonstrate that the Salkowski assay is not a reliable method for measuring the IAA content of
Azospirillum
culture medium and that estimates in excess of 10 μg of IAA ml
−1
should be viewed with particular caution. Metabolism of [2′-
14
C]IAA by
A. brasilense
703Ebc yielded radiolabeled indole-3-methanol, whereas roots of maize (
Zea mays
L.) seedlings gave rise to [
14
C]oxindole-3-acetic acid and an array of polar metabolites. Metabolism of [2′-
14
C]IAA by maize roots inoculated with
A. brasilense
703Ebc produced a metabolic profile characteristic of maize rather than
Azospirillum
species.