Classification of nitrogen treatment-regulated genes into defined functional categories. (a) Venn diagram displaying the number of genes identified in either or both the high NH4+ vs. water and low NH4+ vs. water comparisons. (b) Affymetrix probeset sequences were matched to publicly available Genbank accession identifications and categorized according to tomato or Arabidopsis orthologue gene annotations. Differential expression was analyzed at 53h post treatment. Black bars represent the number of genes more highly expressed in the NH4+ treatment compared to the water treatment, and white bars represent the number more highly expressed in the water treatment compared to the NH4+ treatment. Asterisks indicate a significant difference in the proportion of genes in those functional categories between the high NH4+ vs. water and low NH4+ vs. water comparisons.