The effect of IAA and two IAA precursors, l-tryptophan (Trp) and indole (Ind), on the growth, mineral nutrition and potential development under stress conditions of intact pepper plants cultivated in hydroponic conditions, has been studied. To this end, the growth of both shoots and roots, the plant content of both IAA and free polyamines and the content in leaves and roots of macronutrients and micronutrients have been evaluated. Both Trp and Ind presented a similar pattern of action to that of IAA regarding both plant development and mineral uptake. The application of Ind and Trp at the highest dose (10−3 M) was associated with significant increases of IAA content in roots. The application of IAA and IAA precursors was associated with an increase in Spermine and a decrease in Putrescine in leaves, thus suggesting the conversion of Putrescine into Spermidine and Spermine, which in turn could be associated with better plant development under stress. Both Trp and Ind showed auxin-like effects likely due to their conversion into IAA within the plant. However, further studies carried out under axenic conditions are needed in order to clarify this question.