NITROGEN NUTRITION AND N-ASSIMILATION IN MAIZE SEEDLINGS

Abstract

The effect of ammonia on plant growth is influenced by the stage of growth and concentration of N. This study evaluates the activity of enzymes involved in NH4+ assimilation and the relationship of these enzymes to maize seedling development. Various concentrations of NH4Cl applied at 3, 8, 13, 18 and 23 days after germination were evaluated. Activities of glutamate synthase and glutamine synthetase were not altered when NH4+ was applied to 3-day-old seedlings; however, there was increased enzymatic activity whe N was applied to 18- or 23-day-old seedlings. Glutamate dehydrogenase appears to be an important enzyme for the assimilation of NH4+ by roots of maize seedlings. The growth rate of seedlings receiving NH4+ varied at different stages of development. Prolonged N stress (longer than 18 days) reduced the rates of subsequent dry matter accumulation, indicating that an adequate availability of N throughout early growth is critical for maximum nutrient efficiency and optimum plant development. Greatest growth was observed with a combination of both NO3− and NH4+ sources of N.Key words: Corn, nitrogen nutrition, enzymes (N assimilating), seedling development