Characterization of a substance produced by Azospirillum which causes branching of wheat root hairs

Abstract

Previous studies have shown that Azospirillum or its culture filtrates induce root hairs in wheat seedlings to branch; this phenomenon is influenced by the bacterial genome at the strain level and by the plant genome at the cultivar level. Strain Sp245 caused most branching of root hairs; between wheat cultivars frequency of branching increased in the following order; cv. Tobari, cv. Tonari, cv. BH1146, cv. Lagoa. Similarly plant growth response to inoculation with Azospirillum measured in mature plants, increased in the same order, suggesting that both phenomena (root hair branching and plant growth response) have a similar basis. In this study, the branching substance present in Azospirillum culture filtrate was found to be thermostable at 100.degree. C, removed by dialysis, present in the acidic nonpolar fraction of the cell-free extract and cochromatographed with authentic IAA on thin-layer chromatograms. Purified IAA caused branching of root hairs similar to that caused by the Azospirillum culture filtrates. Susceptibility of wheat cultivars to IAA induced branching increased in the order cv. Tobari, cv. Tonari, cv. BH1146, cv. Lagoa. Of 5 strains examined, strain Sp245 produced the most IAA in culture in the presence of tryptophan. The presence of IAA was confirmed by gas chromatography-mass spectrometry.