The goal of this experiment is to identify the changes in protein expression induced by Al treatment with a view towards developing a molecular level understanding of Al tolerance in an important crop species. In this particular experiment the focus was on protein expression in tomato embryo. Tomato (Solanum lycopersicum ‘Micro-Tom’) plants were treated in Magnavaca’s solution (pH 4.5) supplemented with 50 µM AlK(SO4)2·12H2O providing 7.5 µM Al3+ activity over a four-month period beginning at the emergence of the first flower buds and ending when a few leaves started to turn yellow. Proteins from root, leaf, embryo and seed-coat tissues were identified using a 8-plex iTRAQ labeling strategy followed by a two-dimensional (high- and low-pH) chromatographic separation, and final generation of MS/MS spectra of tryptic peptides on an LTQ-Orbitrap Elite-mass spectrometer