Antioxidant performance and aluminum accumulation in two genotypes of Solanum lycopersicum in response to low pH and aluminum availability and under their combined stress

The mechanisms of Aluminum (Al) tolerance are dependent on the plant species and genotypes, but the results attributed to the toxic effect of Al can also be influenced by pH. Our aim was to study the effect of Al and pH in the antioxidative system of two tomato genotypes in response to Al in hydroponic system. The genotypes Moneymaker (MM) and Calabash Rouge (CR) were grown in Hoagland and Arnon (1950) nutrient solution pH 6.0 until the complete establishment in hydroponic system. Then the plants were transferred to the treatments: minimum medium at pH 4.2, minimum medium at pH 6.5 and minimum medium pH 4.2 + 20 mmol L−1 AlCl3.6H2O. The sampling of plant material was performed in the times: zero (immediately before exposure to the treatments), 24 and 48 h after their beginning. Aluminum accumulation in MM roots was higher than in CR after 48 h. The highest hydrogen peroxide (H2O2) concentration was observed in the shoots at control and at low pH without Al in the roots of CR. Malondialdehyde (MDA) concentration in CR roots did not present alteration along the 48 h, remaining near or below the control, whereas genotype MM presented a lower MDA concentration after 48 h in the presence of Al in relation to CR. In the roots of the genotype CR, superoxide dismutase (SOD) activity was lower at pH 4.2+Al and higher at pH 4.2. We evidenced that the antioxidative system seems more involved in response to low pH than Al toxicity, and that genotype CR presents mechanisms of Al tolerance possibly more related to the lower Al translocation from roots to shoots than with the protective activity of antioxidant enzymes.