ACCUMULATION AND PARTITIONING OF NITROGEN AMONG PLANT-PARTS IN THE HIGH AND LOW-PROTEIN STRAINS OF MAIZE

The objective of this study was to determine the relative contribution of the maternal plant in controlling the characteristic differences b etwen the Illinois High Protein (IHP) and Illinois Low Protein (ILP) m aize strains; which differ in relative content of starch and protein i n the endosperm. In this paper, field experiments were undertak en to analyze the response of the IHP and ILP strains at increasing rates of N fertilizer and to follow the partitioning of N-15 applied and the s ubsequent remobilization of this N in the whole plant during the grain filling period. The level of activity of two enzymes that play a cent ral role in the flow of N into organic compounds of plant cells, was a lso investigated. The results of this study showed that IHP and ILP st rains differed in dry matter production during grain development, in t he amount of reduced-N accumulated, and in the partitioning of N to th e grain. In addition, the supplies of N-15 showed between the IHP and ILP plants a different pattern of remobilization of reduced-N from veg etative plant parts to the developing kernels. Also, it was clearly ev ident that redistribution of reduced-N from stalk to the grain of ILP was practically absent. Enzymatic activity assays for nitrate reductas e (NR) and glutamine synthetase (GS) in the stalk and leaves indicated that ILP plants contained a lower activity of NR in leaves and a lowe r GS activity in the stalk compared to IHP plants.