Isotopic study of post-anthesis foliar incorporation of sulphur and nitrogen in wheat.

Nitrogen (N) and sulphur (S) supplies have a strong influence on the quality and quantity of wheat storage proteins, which play an important role in the bread-making process. In order to relate the incorporation and distribution of foliar N and S fertilisers at the post-anthesis stage to the quality of wheat, 15N and 34S isotopes were used as tracers. The incorporation of these tracers in different plant parts (leaves, stems, ears) and in each storage protein fraction (gliadins, HMW and LMW glutenin subunits) was determined by isotopic ratio mass spectrometry coupled with an elemental analyser (EA-IRMS). By this means, the true recovery coefficient of N and S (TRCNfertiliser and TRCSfertiliser) and the N and S derived from fertilisers (Ndff and Sdff) could be determined. The TRCNfertiliser and TRCSfertiliser values of the different plant parts provide evidence of the applied N and S assimilation and translocation from wheat leaves to the seeds. The determination of Ndff and Sdff incorporated into storage proteins shows the efficiency and the influence of N and S incorporation into each storage protein fraction. Moreover, a favourable stage for fertiliser application can be determined by the TRCNfertiliser values in the grain and in the whole plant. The fertilisers enriched in stable isotope used in the culture techniques can be a means of understanding the effectiveness of fertilisers in the expression of wheat quality.