Identification and quantification of IAA and IBA in Azospirillum brasilense-inoculated maize roots

Abstract

Inoculation of maize seedlings with 10 7 colony forming units (cfu) of Azospirillum plant −1 significantly increased the root surface area 2 weeks after sowing as compared to non-inoculated plants. Indole-3-acetic acid (IAA) was identified by gas liquid chromotography (GLC) and gas chromatography-mass spectrometry (GC-MS) in Azospirillum tryptophan-free culture medium. The amount of IAA in the medium was calculated from the gas chromatogram by isotope dilution analysis and found to be 32–40 ng ml −1. Roots of Azospirillum-inoculated maize seedlings were found to have higher amounts of both free and bound IAA as compared to control. The amount of free IAA significantly increased in the inoculated roots 2 weeks after sowing. IAA and indole-3-butyric acid (IBA) were identified by GC-MS only in the roots of Azospirillum-inoculated seedlings 2 weeks after sowing. The significance of the higher amounts of IAA following inoculation with the bacteria is discussed.