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

Incorporation of ^<15>NH_4-N and ^<15>NO_3-N into an insoluble (protein) fraction was examined 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 proportion of the protein nitrogen content to the total nitrogen content was also higher in all the tissues of the ammonium-plant. A considerable part of nitrogen absorbed during ^<15>N application (^<15>N) remained in the roots of the ammonium-plant as compared with the nitrate-plant. On the other hand, a larger amount of ^<15>N accumulated in a stem of the nitrate-plant. The proportion of protein-^<15>N to total ^<15>N was higher in all the tissues of the ammonium-plant than in the nitrate-plant. These results suggest that even after 6 days\u27 treatment with 100ppm of NH,-N, absorbed ammonium nitrogen was utilized for the protein synthesis at least at the same rate as NO,-N in the nitrate-plant