Incorporation of Inorganic Nitrogen into Protein Fraction in Tomato Plants Grown with Ammonium and Nitrate as Nitrogen Sources

Incorporation of 15NH,-N and‘5NO,-N into an insoluble (protein) fraction was exam-ined in the tomato plants previously grown with NH,-N and NO,-N for 6 days. Each tissue of the ammonium-plant except a stem and roots had a higher total nitrogen content than that of the nitrate-plant.An insoluble nitrogen content was higher in all the tissues of the ammonium-plant than in those of the nitrate-plant.The propor-tion of the protein nitrogen content to the total nitrogen content was also higher in al l the t issues of the ammonium-plant.A considerable part of nitrogen ab-sorbed during ‘5N application (‘5N) remained in the roots of the ammonium-plant as compared with the nitrate-plant.O the other hand, a larger amount of 15N accu-mulated in a stem of the nitrate-plant.The propor t ion o f protein-‘5N to total 15N was higher in al l the t issues of the ammonium-plant than in the nitrate-plant. These results suggest that even after 6 days ’ treatment with 100ppm of NH,-N, ab-sorbed ammonium nitrogen was uti l ized for the protein synthesis at least at the same rate as NO,-N in the nitrate-plant.