Egle, K., Beschow, H. and Merbach, W. 2015. Nitrogen allocation in barley: Relationships between amino acid transport and storage protein synthesis during grain filling. Can. J. Plant Sci. 95: 451-459. A better knowledge of the source-sink relationships relating to nitrogen allocation within plant and synthesis of storage protein in grains could be of particular importance contributing to better define grain sink capacity for improving nitrogen use efficiency by plant species. The objectives of this study were to assess N partitioning in barley cv ‘Barke’prior and after anthesis, and to investigate whether the synthesis of the major storage protein (hordein) is an indicator of the sink strength of the developing grain for nitrogenous compounds. Pot experiments were performed using N fertilizer, labelled N (¹⁵N fertilizer) or feeding of labelled proteinogenic and non-proteinogenic amino acids (¹⁵N-L-a-alanine: ¹⁵N-a-Ala or ¹⁵N-a-aminoisobutyric acid: ¹⁵N-a-Aib, respectively). Results showed that N filling of spike occurred from N remobilized predominantly from leaves and stem, and from current N uptake. Post-anthesis applied ¹⁵N was taken up and predominantly transported into spike. Experiment with feeding of labelled amino acids demonstrated that most of the ¹⁵N from a-Ala and a-Aib was transferred to grains, but that more (about 37% versus 24%) was retained in the fed leaf when ¹⁵N was applied in the form of a-Aib. The strongest effect was observed in partitioning between N fractions in grains: hordein acted as a main reservoir for ¹⁵N-a-Ala while ¹⁵N-a-Aib predominantly remained in NaCl-extractable fractions (non-protein nitrogen and salt-soluble proteins). The biosynthesis of hordein in grains did not seem to be exclusively the potential sink for nitrogenous compounds but could enhance the transport of amino acids into the grain by the instantaneous incorporation of imported amino acids into hordein.