One of the major factors that affect plant growth in acid soils (pH < 5) is aluminum (Al) toxicity. Aluminum is the most abundant metal in the earth's crust, representing about 8% of total mineral components. Under acidic condition, Al is hydrolyzed into the soluble major phytotoxic form, Al³⁺. This study was conducted to localize Al in tomato plant tissues, including fruits. Also to determine protein expression in seed tissues of matured green fruits under Al stress. Tomato (Solanum lycopersicum cv. Micro-Tom) plants were grown in hydroponic tanks filled with Magnacava’s solution, pH 4.5 - 4.6.  For Al treatment, the hydroponic solution was supplemented with 50 µM AlK (SO₄)₂. 12H₂O, and the control was refreshed with only the Magnacava’s solution. Cross sections of roots, stems and green fruits were stained with morin (2’, 3, 4’, 5, 7-pentahydroxyflavone) fluorochrome to track and detect Al in situ. The Al-treated tissues showed brighter green fluorescence than the untreated ones. Differentially expressed proteins between the Al-enriched seeds and controls were identified using two-dimensional gel electrophoresis (DIGE) analysis followed by a procedure of in-gel trypsin digestion-mass spectrometry-database search (the annotated tomato database). Results showed that the identified proteins are involved in gene expression and cell division, chaperones and protectants, metabolic pathways, and phytohormone-biosynthesis. Also, elevated expression level of malic enzymes and antioxidant enzymes was observed. Based on these results, a molecular model of ion toxicity from endogenous Al during seed maturation and germination is being evaluated.