Essential for nitrogen assimilation, distribution and remobilization within the plant via the phloem. ATP + H2O + L-aspartate + L-glutamine = AMP + diphosphate + H(+) + L-asparagine + L-glutamate Amino-acid biosynthesis; L-asparagine biosynthesis. Expressed in the vascular region adjacent to leaf mesophyll cells in the companion cell-sieve tube element complex. By light and sucrose. Down-regulated by dark. Pale green leaf phenotype and reduction of biomass in mature plants. Increased levels of asparagine, proline and ammonium in response to salt treatment.