NITROGEN NUTRITION AND SEEDLING DEVELOPMENT OF NORMAL AND OPAQUE-2 MAIZE GENOTYPES

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Abstract
Early seedling growth and glutamine synthetase and glutamate dehydrogenase activities of the normal and opague-2 (o2) genotypes of maize were compared in the presence or absence of added N. In the absence of exogenous N, the dry weight of o2 seedlings was only 60% of the dry weight of normal seedlings at 21 days after germination; however, the dry weights were comparable when exogenous N, especially as NO−3, was supplied to both genotypes. Thus, exogenous N appears to be more critical for early growth of o2 than normal seedlings. Growth of o2 seedlings was more severely restricted than of the normal genotype by high concentrations of NH+4. A combination of NH+4 and NO−3 resulted in better growth of both genotypes than either form on N alone. There was no difference in the capacity of the two genotypes to accumulate N from exogenous NH+4 or NO−3. However, both genotypes accumulated relatively more N from NH+4 than from NO−3. Glutamine synthetase activity in o2 roots was twofold higher than in the normal genotype in the absence of exogenous N but was similar in the roots of both gentoypes when seedlings were grown in either NO−3 or NH+4. In the absence of exogenous N, glutamate dehydrogenase activity in o2 roots was 2.8-fold higher than in normal roots and remained higher when NH+4 was added.Key words: Nitrogen form, ammonium, nitrate, glutamate dehydrogenase, glutamine synthetase, zein