Amino acid concentrations in root and leaf extracts of plants during the progression of Fe deficiency treatment. Sampling was performed at 0, 1, 3, 7 days after Fe withdraw. The meaning of the columns is as reported in Figure 2. Abbreviation: Asp, aspartate; Asn, asparagine; Glu, glutamate; Gln, glutamine; Ser, serine; Gly, glycine; Arg, arginine (complete aa amounts data are reported in Additional file 2). Data are means ± SE (n = 4). In the case of significant difference (P<0.05) values with different letters are statistically different.