Fig. 4.

Time course of the expression of five genes significantly regulated by short-term nitrate/ammonium treatments in Zea mays L. roots (A) and leaves (B). Data are reported as base-2 logarithm of the ratio between the expression levels measured for samples subjected to the treatments, as described in Fig. 1 (short-term nitrogen starvation in seedlings grown in +N conditions and short-term nitrogen provision in seedlings grown in –N conditions) and of its own control. The left column (–) shows the differences in gene expression in seedlings supplied for 5 days with NO₃ ^– (upper part) or NH₄ ⁺ (lower part) and then deprived for 30min, 2h, and 6h; the right column (+) shows the differences of expression measured after resupply with NO₃ ^– (upper panels) or NH₄ ⁺ (lower panels) for 30min, 2h, and 6h in seedlings grown 5 days in a N-deprived medium.