Impact of nitrogen source on gene expression patterns. Genes differentially expressed between leaf samples (a) and root samples (c) due to the nitrogen source. Heatmaps of gene expression profiles, represented by Z-scores; red indicates a positive Z-score, blue indicates a negative Z-score. (b) auxin response factor expression in leaves. (d) nitrogen transporter expression; plants provided with NO3− up regulate low affinity N transporters 1 and 3, while N deficient plants up regulate high affinity transporter NRT2. Plants fixing N2, show an increased expression of NRT1.