1. The Neon sunflower genotype, when grown with NNH4+, presented higher Vmax in comparison with the plants supplied with N-NO3-;
2. Although presenting the lowest Vmax value, the plants supplied with 2.0 mmol L-1 of N-NO3- presented higher biomass than those supplied with the same dose of NNH4+, which can indicate a greater potential for use of nitric N;
3. There was no difference in accumulation of biomass in the plants grown with the lowest N dose (0.2 mmol L-1), suggesting that in the conditions of this experiment,there is no preference for the N source;
4. The petiole is the preferential organ for accumulation of N-NO3-.