Nitrogen redistribution in spring wheat

This thesis summarises solution culture experiments studying pre- and postanthesis nitrogen translocation and distribution in spring wheat (Triticum aestivum L.) Partitioning of biomass and harvest index (HI) were dependent on phenological development rate. Nitrogen concentration in plant parts during growth was more dependent on development rate than on N supply. The remaining nitrogen concentration in the plant parts at maturity was dependent on nitrogen concentration during growth. The roots were the last vegetative part to senesce and were competitors with the grain during late grain filling in respect of nitrogen. The capability to take up, distribute and redistribute nitrogen was maintained after complete yellowness. A considerable amount of nitrogen was redistributed from the roots to the grain during grain filling. At maturity, the roots contained 10-20% of all plant nitrogen. Genetic variation was found for root nitrogen concentration. Root weight was negatively correlated with grain nitrogen concentration, nitrogen harvest index (NHI) and total nitrogen harvest index based on the entire plant (NHItot). Nitrogen concentration in grain in different spikelet positions reached end concentration 14 days before grain filling was completed. During late grain filling, nitrogen accumulation in the spikelets ceased from top to base in the spike. Differences in protein composition and polymerisation of protein between spikelets were observed in one of two cultivars. The last nitrogen taken up was incorporated into all types of protein within a spikelet. Response to temperature differed between cultivars. An appropriate response to temperature was important in achieving high HI, high nitrogen redistribution to the grain and high NHI. Two different ways to achieve high nitrogen concentration in the grain were distinguished. High grain nitrogen concentration in a cultivar was due to either high rate of nitrogen redistribution from vegetative parts to the grain or low root weight and low shoot weight. The results presented in this thesis provide new knowledge about nitrogen redistribution in the plant, nitrogen accumulation and protein polymers within the spike.