Karuppanapandian, T., Rhee, S.-J., Kim, E.-J., Han, B. K., Hoekenga, O. A. and Lee, G. P. 2012. Proteomic analysis of differentially expressed proteins in the roots of Columbia-0 and Landsberg erecta ecotypes of Arabidopsis thaliana in response to aluminum-toxicity. Can. J. Plant Sci. 92: 1267–1282. Aluminum (Al) is phytotoxic when solubilized into Al3+ in acidic soils and represents a major constraint for crop production. The present study describes Al-stress responses in roots of Al-tolerant and Al-sensitive Arabidopsis ecotypes, Columbia-0 (Col-0) and Landsberg erecta (Ler), respectively. Comparative proteomic analysis was applied to plants grown in hydroponic solution culture under acidic pH (4.2) conditions. To investigate time-dependent responses, 6-d-old seedlings were treated with 30 µM AlCl3 for 24, 48, or 72 h; total proteins were prepared from roots and separated by two-dimensional gel electrophoresis (2-DE). From 2-DE analysis, were 600 proteins were inspected, 29 proteins were differentially responsive to Al-treatment. The 2-DE patterns were compared and differentially expressed proteins identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Analysis of protein expression patterns revealed that a set of proteins is functionally associated with tricarboxylic acid (TCA) cycle and glycolysis, reactive oxygen quenching and detoxification mechanism, and signal transduction pathways, etc., could play important roles in mediating plant response to Al in Arabidopsis ecotypes. Comparison of the changes in the protein profiles revealed that Al-stress increased Al-tolerance related proteins in Al-tolerant Col-0, but only generic stress responses occurred in Al-sensitive Ler. Specifically, Al up-regulated proteins such as alcohol dehydrogenase, monodehydroascorbate reductase, GTP-binding nuclear protein Ran-2, and leucine aminopeptidase in Col-0 but not in Ler.