Accumulation and remobilization of nitrogen in a vegetative winter wheat crop during or following nitrogen deficiency

Nitrogen (N) deficiency leads to retranslocation of N from shoots to roots in vegetative winter wheat plants grown under controlled conditions. The accumulation and remobilization of nitrogen were quantified for each individual organ of winter wheat plants grown in the field, during a 3-week period of N deficiency (no fertilization) or during the relief of N deficiency (fertilizer applied), during stem elongation. The rate of accumulation of N directly from the soil and the rate of remobilization of N from different organs were determined independently, using double-crossed N-15 labelling. The decrease in soil N availability during the first week of the study period reduced the rate of N accumulation by 75 %. This low level of N accumulation affected the three uppermost leaves. At the end of the 3-week study period, nitrogen had been remobilized from the stems and lower leaves and transported to the three uppermost leaves of fertilized plants and to the two uppermost leaves of the deficient plants. In this case, the third leaf from the top remobilized 40 % of total nitrogen translocated. The roots accumulated 11 to 17% of total nitrogen during the first week of the study period, and this was then translocated to the upper leaves. This reversal of the source-sink relationships between organs reflects the ability of the plant to compensate for limited periods of N shortage, using remobilized N for growth. (C) 1999 Annals of Botany Company.