GENOTYPIC DIFFERENCES IN NITRATE UPTAKE AND NITROGEN-UTILIZATION FOR SPRING WHEAT GROWN HYDROPONICALLY

The physiological background for variation in grain protein content of cultivars of spring wheat (Triticum aestivum L.) is still unclear. Th is study was performed to investigate whether differences in nitrate u ptake and nitrogen utilization could explain the observed differences. Four cultivars of spring wheat were grown hydroponically to maturity. Growth was controlled by daily additions of growth-limiting amounts o f nitrate at preset and stepwise decreased relative rates. The plants showed a relevant ontogeny when compared to field-grown plants. The ki netics of net nitrate uptake were measured regularly from 16 to 102 d of culturing. The maximal net nitrate uptake rate of the plant, i.e., V-max, increased until anthesis, and subsequently decreased. There wer e no major changes in the affinity for nitrate, i.e., K-m during the d evelopment. When uptake capacity was put in relation to the need of th e plant in order to maintain growth rate and tissue-nitrogen concentra tion, it was clear that the plants had a substantial overcapacity for net nitrate uptake at all times. There were no major genotypic differe nces in either V-max or K-m. Frequent sampling of plants made it possi ble to calculate the remobilization of nitrogen from vegetative tissue s to the grains, and these data could be used to discuss further diffe rences in grain protein yield.