Aluminum-induced oxidative stress in maize

The relation between Al-toxicity and oxidative stress was studied for two inbred lines of maize (Zea mays L.), Cat100-6 (Al-tolerant) and S1587-17 (Al-sensitive). Peroxidase (PX), catalase (CAT) and superoxide dismutase (SOD) activities were determined in root tips of both lines, exposed to different Al3+ concentrations and times of exposure. No increases were observed in CAT activities in either line, although SOD and PX were found to be 1.7 and 2.0 times greater than initial levels, respectively, in sensitive maize treated with 36 muM of Al3+ for 48 h. The results indicate that Al3+ induces the dose- and time dependent formation of reactive oxygen species (ROS) and subsequent protein oxidation in S1587-17, although not in Cat100-6. After exposure to 36 muM of Al3+ for 48 h, the formation of 20+/-2 nmol of carbonyls per mg of protein was observed in S1587-17. The onset of protein oxidation took place after the drop of the relative root growth observed in the sensitive line, indicating that oxidative stress is not the primary cause of root growth inhibition. The presence of Al3+ did not induce lipid peroxidation in either lines, contrasting with the observations in other species. These results, in conjunction with the data presented in the literature, indicate that oxidative stress caused by Al may harm several components of the cell, depending on the plant species. Moreover, Al3+ treatment and oxidative stress in the sensitive maize line induced cell death in root tip cells, an event revealed by the high chromatin fragmentation detected by TUNEL analysis. (C) 2003 Elsevier Science Ltd. All rights reserved.62218118

Differences in Al tolerance between Plantago algarbiensis and P. almogravensis reflect their ability to respond to oxidative stress

We evaluated the impact of low pH and aluminum (Al) on the leaves and roots of Plantago almogravensis Franco and Plantago algarbiensis Samp., focusing on energy partitioning in photosystem II, H2O2 levels, lipid peroxidation, electrolyte leakage (EL), protein oxidation, total soluble protein content and antioxidant enzyme activities. In both species, Al triggered more changes in oxidative metabolism than low pH alone, particularly in the roots. We found that Al increased the levels of H2O2 in P. algarbiensis roots, but reduced the levels of H2O2 in P. almogravensis leaves and roots. Neither low pH nor Al affected the spatial heterogeneity of chlorophyll fluorescence, the maximum photochemical efficiency of PSII (F-v/F-m), the actual quantum efficiency of PSII (I center dot(PSII)) or the quantum yields of regulated (I center dot(NPQ)) and nonregulated (I center dot(NO)) energy dissipation, and there was no significant change in total soluble protein content and EL. In P. algarbiensis, Al increased the carbonyl content and the activities of superoxide dismutase (SOD) and catalase (CAT) in the roots, and also CAT, ascorbate peroxidase and guaiacol peroxidase activities in the leaves. In P. almogravensis, Al reduced the level of malondialdehyde in the roots as well as SOD activity in the leaves and roots. We found that P. almogravensis plantlets could manage the oxidative stress caused by low pH and Al, whereas the P. algarbiensis antioxidant system was unable to suppress Al toxicity completely, leading to the accumulation of H2O2 and consequential protein oxidation in the roots