Maize growth and ammonium assimilation enzyme activity in response to nitrogen forms and pH control1

Plant growth, glutamine synthetase and glutamine dehydrogenase activities of two maize genotypes were compared in the presence of NH4 + and NO3 ‐ forms of N in sand culture. Ammonium reduced growth of the P3732 genotype 64% and the B73 x Mol7 hybrid 59% as compared to NO3 ‐. Both glutamine synthetase and glutamate dehydrogenase activities in roots tended to be higher with NH4 as compared to NO3. As the pH in the medium was increased by adding CaCO3, glutamine synthetase and glutamate dehydrogenase activities in roots of both genotypes were reduced; however, glutamine synthetase activity in leaves of NH^‐treated plants increased at the higher pH of the growing medium.