Metabolomic Analysis Reveals Patterns of Whole Wheat and Pearling Fraction Flour Quality Response to Nitrogen in Two Wheat Lines with Contrasting Protein Content

Nitrogen (N) application increases wheat yield and protein content and affects the nutritional quality of the grain. Analysis of N use efficiency revealed that N uptake efficiency is a key factor affecting protein content. Two wheat lines with significant differences in protein content were used to investigate the response of differential accumulation of metabolites to N levels and the spatial variation pattern of metabolites related to nutritional quality in wheat grains using widely targeted metabolomics analysis. The results showed that amino acids, nucleic acids, and phytohormones and their derivatives and glycolytic processes are the crucial factors affecting protein content in two wheat lines. Amino acids and derivatives, lipids, and flavonoids are the main contributors to metabolite spatial variation of grains, which were interactively regulated by nitrogen and genotypes. N application significantly increased the relative accumulation of beneficial bioactive substances in the inner layer (P3 to P5), but excessive N application may inhibit this effect and lead to poor nutritional quality.