Effect of water-soluble vitamins on the production of indole-3-acetic acidby Azospirillum brasilense

The effects of six water-soluble vitamins on tryptophan-dependent synthesis of indole-3-acetic acid in Azospirillum brasilense were investigated. A mu ltifactorial regression analysis was employed to produce models of indole-3 -acetic acid synthesis versus concentrations of tryptophan and the vitamins added to the growth medium. Very low levels of the B-group vitamins added at 10 to 100 mu g l(-1) affected production of indole-3-acetic acid in A. b rasilense. The largest release of this phytohormone was observed after amen dment with pyridoxine and nicotinic acid. Results of the study suggest a ro le these vitamins may fulfil in the regulation of indole-3-acetic acid synt hesis in A. brasilense.