Distribution of nitrogen absorbed during different times of growth in the plant parts of wheat and contribution to the grain amino acids

Abstract

Wheats (Triticum aestivum L. cv. Nörin 61) were grown in culture solution in a greenhouse. The growth season was divided into six periods, and ¹⁶N labeling was applied during each period to different plants by supplying ¹⁶N-labeled KNO₃. Partitioning of the label in the plant parts and in the pro teins and amino acids of the grains was investigated.

Loss of nitrogen (N) from the plants was observed only for N absorbed early. N in each plant part was composed of newly absorbed N and retranslocated N, and N loss from a part was faster in the case of late partitioned N than early partitioned N. A considerable amount of N was estimated to be transferred to the ears after being distributed to other parts.

No significant differences in the distribution of the N absorbed at the different times of growth among the protein fractions of the grains were detected. Although the grain amino acids were synthesized with the N supplied any time during the growing season, there were some distinct differences in the preferential dependence of N origin on the time of N absorption. The dependence of lysine, histidine+arginine, and valine on early absorbed N was relatively more pronounced than in the case of glutamic acid, aspartic acid, and alanine, while the reverse was observed for N absorbed in later stages of growth.