Identification of molecular and physiological changes in tomato in responses to aluminum stress and functional studies of aluminum responsive genes

Aluminum (Al) is one major toxic ion in acid soil (pH\u3c 5.0). This study aimed to determine the physiological and molecular changes induced by Al in tomato (Solanum lycopersicum \u27Micro-Tom\u27). Tomato plants were grown in hydroponic culture, and Al treatment was applied using 50&mgr;M aluminum sulfate [Al2 (SO4)3•18H 2O] or 50&mgr;M aluminum potassium sulfate dodecahydrate [KAl(SO 4)2•12H2O]. Mineral analysis found that Al 2(SO4)2 treated tomato contained a significant higher amount Al in roots (29-fold), and in green and orange and red tomato fruits (2-fold) (p\u3c 0.05). Morin (2\u27, 3, 4, 5, 7-pentahydroxyflavone) staining also detected a higher fluorescence intensity on Al treated roots. The treatment with aluminum potassium sulfate dodecahydrate resulted in shorter roots and a four-fold decrease in root size. In the relative and absolute quantitation (iTRAQ) proteomics analysis, 1442 proteins were identified in roots, of which 34 proteins showed significant changes in abundance between the Al-treated and control tissues (t- test with FDR corrections, p\u3c0.05, and \u3e 1.2-fold). Based on their putative cellular functions, the identified proteins are involved in metabolism of cell wall materials, plasma membrane changes, signal transduction, proteolysis, gene transcription, TCA cycle, glycolysis and detoxification . In green, orange and red tomato fruits, 124 of 1133 proteins, 39 of 1362 proteins, 44 of 1362 proteins, showed significant changes in abundance between the Al-treated and control tissues in each tissue type, respectively. Based on molecular functions, the identified proteins are involved in metabolism of cell wall materials, protein translation, energy regeneration, carbohydrate metabolism (glycolysis, TCA cycle, pentose phospate pathway, photosynthesis), intracellular trafficking protein, stress proteins (heat shock proteins, chaperonin, antioxidative enzymes, detoxification), post-translational modification and targeting and proteolysis, signal transduction and seed storage proteins. Proteins that are common to green, orange and red fruits (404 proteins), or those present only in one of the three maturity stages (395) were identified. Changes in those proteins corroborate with physiological processes, such as photosynthetic proteins were found only in green fruits. Transgenic tomato `Money Maker\u27 plants over expressing a lactoylglutathione lyase gene were generated. Three transgenic lines were confirmed to contain the insert gene. These transgenic lines are currently being evaluated for tolerance to Al toxicity