the invention is drawn to plant cell transformation with a nucleic acid construct comprising a prokaryotic ammonium - specific asparagine synthetase , type a , coding sequence , operably linked to a chloroplast transit peptide - encoding sequence , wherein said plant cells also contain a nucleic acid construct comprising a chloroplastic glutamine synthetase coding sequence in antisense orientation . plant cells containing both nucleic acid constructs , and plants regenerated therefrom , exhibit improved growth characteristics .