THE UTILIZATION OF AMMONIUM CHLORIDE-15N BY UREDOSPORES OF WHEAT STEM RUST

Abstract

When uredospores of wheat stem rust, Puccinia graminis van tritici (race 15B), were incubated with a 3 mM solution of ammonium chloride-15N, a significant amount of nitrogen 15 was converted into organic nitrogen. Most of this organic nitrogen 15 was found in the ethanol and water extracts, with lesser amounts in the buffer and in extracted spores.Amino acids extracted from the spores all contained excess nitrogen 15. Nitrogen 15 from the inorganic source was diluted by factors of 1.7 and 2.7 in free aspartic and glutamic acids respectively; these amino acids were the most heavily labeled with the isotope. Proline was the most weakly labeled amino acid, the nitrogen 15 being diluted by a factor of 102. Good incorporation of nitrogen 15 into glutamic acid compared to simultaneous poor incorporation into the biochemically related amino acid, proline, parallels previous observations made during carbon 14 experiments with rust uredospores.Fourteen "bound" amino acids were isolated after acid hydrolysis of extracted spores. All contained nitrogen 15, the dilution of the added ammonia nitrogen ranging from 96 for glutamic acid to 7660 for proline.The results are taken as evidence that uredospores of wheat stem rust can incorporate ammonium nitrogen into free amino acids and into proteins.