Cluster analysis of free amino acid profiles during seed development. Amino acids were classified using k-means analysis into five groups. The names of amino acids belonging to each group are indicated on the right. Data on the y axis is the amino acid content (see Additional file 1) normalized to the average and expressed in log2 scale. Developmental stages are named according to Walbot et al. . Timing of phaseolin (Phs) and phytohemagglutinin (Pha) transcript and phaseolin protein accumulation is according to Bobb et al. .