INOCULATION WITH AZOSPIRILLUM-LIPOFERUM AFFECTS GROWTH AND GIBBERELLIN STATUS OF CORN SEEDLING ROOTS

Maize (Zea mays L., hybrid Cargill 147) seedlings, grown in aseptic co nditions, were inoculated with three strains of Azospirillum lipoferum (Al op 33, Al iaa 320, and ATCC 29708) or cultured in different conce ntrations of indol-3-acetic acid (IAA) or gibberellin A3 (GA3). After 48 h, root length, root surface area, root dry weight, and shoot dry w eight were measured in all treatments. Gibberellin content was evaluat ed in selected roots of control and Azospirillum inoculated seedlings by gas chromatography-mass spectrometry-selected ion monitoring with t he use of deuterated gibberellins as internal standards. The three str ains of A. lipoferum, IAA (2 ng ml-1), and GA3 (40 to 400 pg ml-1) sig nificantly enhanced root growth. Improvement of root hair growth and d ensity was obtained mainly with A. lipoferum strain Al op 33 and GA3 4 0 pg ml-1. GA3 Was identified by gas chromatography-mass spectrometry (by both, full scan and selected ion monitoring) in a free acid fracti on from roots of the seedlings inoculated with A. lipoferum. In the ro ots of the non inoculated seedlings GA3 was found after hydrolysis of a fraction expected to contain glucosyl conjugates.