REGULATION OF NITRATE UPTAKE BY AMINO-ACIDS IN MAIZE CELL-SUSPENSION CULTURE AND INTACT ROOTS

The effect of amino acids on nitrate transport was studied in Zea mays cell suspension cultures and in Zea mays excised roots. The inclusion of aspartic acid, arginine, glutamine and glycine (15 mM total amino acids) in a complete cell-culture media containing 1.0 mM NO3 strongly inhibited nitrate uptake and the induction of accelerated uptake rate s. The nitrate uptake rate increased sharply once solution amino acid levels fell below detection limits. Glutamine alone inhibited inductio n in the cell suspension culture. Maize seedlings germinated and grown for 7 days in a 15 mM mixture of amino acids also had lower nitrate u ptake rates than seedlings grown in 0.5 mM Ca(NO3)(2) or 1 mM CaCl2. A s amino acids are the end product of nitrate assimilation, the results suggest an end-product feed-back mechanism for the regulation of nitr ate uptake.