Fig. 1. Schematic representation of amino acid transport between
the sites of primary nitrogen assimilation and the importdependent
tissues. Amino acids synthesized in the root from inorganic
forms of nitrogen or symbiotic relationships are transported
to mature leaf tissue in the xylem. Amino acids synthesized
in the leaf after primary assimilation, or arriving from the
root in the xylem, are transported out of the leaf in the phloem
to satisfy the needs of heterotrophic sinks. Import-dependent
tissues include developing leaves, roots, cortical cells in the
stem, seed and fruits, and apical meristems (from [1] with permission).