(A) Enzymatic activity and (B) Northern Blot analysis of GS and GOGAT. Assay and Northern Blot were performed on root and leaf of plant during the progression of Fe deficiency treatment. Sampling was performed at 0, 1, 3, 7 days after Fe withdraw. The meaning of the columns and the measurement units of enzymatic activities is as reported in Figure 2. Control (0 d) activity of GS was 259 and 520 nmol NADH mg-1 prot min-1, respectively for root and leaf. GS1, root isoform; GS2, leaf isoform. Control activity of GOGAT was 140 and 112 nmol NADH mg-1 prot min-1, respectively for root and leaf. Fd-GOGAT, ferredoxin-dependent isoform; NADH-GOGAT, NADH-dependent isoform (complete activity data are reported in Additional file 1). Data are means ± SE (n = 4). In the case of significant difference (P<0.05) values with different letters are statistically different.