Fig. 5

Schematic presentation of N roadmap for grain gluten quality. Note: The main protein degradation is carry out in flag leaves, resulting in production of free amino acids that are transported from the leaf to the endosperm cavity sap, and subsequently used for protein synthesis in the wheat grain. This transportation flux is indicated with blue arrows. TL3 was used as standard. The bars indicate the relative levels of (TL1, red) and (TL5, blue) of: expression levels of relevant genes for amino acid metabolism, amino acid concentrations and protein content. TL5, TL3 and TL1 indicate topdressing timing of nitrogen in different wheat leaf fifth, third and first leaf (flag leaf) from the top, respectively. The average gene expression of selected genes in leaf (a-f) and endosperm (h-m, o-q) during grain filling stage was used to calculate the relative gene expression change in TL5 and TL1 in comparison to TL3. Total content of free amino acids in the cavity sap at 7 DAA were compared between treatments. The relative changes of average content of other free amino acids in endosperm during the grain filling stage in TL5 and TL1 are shown. The scaling range of vertical axis in all the bar charts is from − 0.5 to 0.5. a, GS2a; b, ASN1; c, AlaAT; d, PPDK; e, Thiol protease; f, Cysteine protease; g, FAA content; h, pyrroline-5-carboxylate reductase; i, phosphoserine aminotransferase; j, arogenate dehydrogenase; k, isopropyl malate dehydrogenase; l, alanine aminotransferase; m, alanine glyoxylate aminotransferase; n, other FAA content; o, HMW-GS; p, LMW-GS; q, PDIL2–1; r, GMP content; s, Glutenin content. FAA, free amino acid