A factor from Azospirillum brasilense inhibits germination and radicle growth of Orobanche aegyptiaca

Cells of the bacterium Azospirillum brasilense contain an alcohol soluble, low-molecular-weight compound (MW of 1000 Da or less) that inhibits the germination and radicle growth of conditioned seeds of Orobanche aegyptiaca, when applied together with the germination stimulant GR24. Partial characterization of the compound suggests that it is a small peptide. A number of synthetic peptides were tested for the inhibitory activity. At least two peptides, one linear and one cyclic, had similar effects on the seeds as those caused by the factor that was extracted and partially purified from cells of A. brasilense. We suggest that the factor present in Azospirillum and the synthetic peptides may act by competing for the site of binding of the germination stimulant.