Aluminum tolerance in maize is correlated with increased levels of mineral nutrients, carbohydrates and proline, and decreased levels of lipid peroxidation and Al accumulation

We investigated the uptake of aluminum (Al) and transport to shoots in two inbred maize lines (Zea mays L., VA-22 and A(4/67)) differing in At tolerance. Seedlings were grown for 7 days in hydroponic culture with nutrient solution that contained 0, 240, 360, and 480 mu M Al at pH 4.2. After 7 days of exposure to Al, roots of sensitive maize line (A4/67) plants accumulated 2-2.5 times more At than roots of tolerant line (VA-22) plants. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that the tolerant line retained higher concentrations of Ca2+ , Mg2+, and K+ compared with the sensitive line. In response to At treatment, proline (Pro) concentration increased three-fold in roots of tolerant plants, while a slight increase was observed in roots of sensitive-tine plants. A substantial carbon surplus (two-fold increase) was observed in roots of the At-tolerant maize line. Carbohydrate concentration remained almost unchanged in roots of At-sensitive tine plants. At treatment triggered the enhancement of lipid peroxidation in the sensitive line, while no change in lipid peroxidation level was observed in the tolerant maize line. These data provide further support to the hypothesis that a mechanism exists that excludes At from the roots of the tolerant maize line, as well as, a internal mechanism of tolerance that minimizes accumulation of lipid peroxides through a higher Pro and carbohydrate content related to osmoregulation and membrane stabilization. (C) 2007 Elsevier GmbH. All rights reserved.