Fig. 4.

Transcriptome heat map for differentially expressed genes of the shikimic acid, tryptophan synthesis, and auxin synthesis-related pathways (A, B) and auxin response-related pathway (C, D) in the shoot and root of maize plants. SCK, ST1, and ST2 indicate the levels of gene expression in the shoot of plants exposed to sole NO₃^–, mixed N, and sole NH₄⁺ supply, respectively. RCK, RT1, and RT2 indicate the levels of gene expression in the root of plants exposed to sole NO₃^–, mixed N, and sole NH₄⁺ supply, respectively. Three repeats were performed for each N treatment. The color gradient illustrates the Z-scores of the gene expression values calculated as the mean-centered log2 (FPKM) values divided by the SD for each gene. Significant difference for each gene was defined as P<0.05 and log2 (FPKM) values ≥1 or ≤–1. Compared with expression in the presence of sole NO₃^– supply, the expression of genes is either up-regulated by mixed N supply (red bracket), up-regulated by both mixed N and sole NH₄⁺ supply (blue bracket), up-regulated by sole NH₄⁺ supply (purple bracket), down-regulated by mixed N supply (black bracket), down-regulated by both mixed N and sole NH₄⁺ supply (green bracket), or down-regulated by sole NH₄⁺ supply (brown bracket).