Abstract:

Salicylic acid (SA) plays an important role in mediating some biotic and abiotic stress-induced oxidative stresses in plants. However, it remains unknown about the role of SA in mediating oxidative stress induced by aluminum. In this study, we investigated the changes in concentrations of H₂O₂ and O₂-, some antioxidative enzyme activities and several physiological parameters involved in oxidative damage to plasma membrane in the root tips of Cassia tora L. Results indicated that 20 mmol/L aluminum (Al) caused increases in electrolytes leakage, malondlaldehyde (MDA) content and intense staining with Evans blue in root tips, while treatment with 5 mmol/L SA suppressed the Al-induced increase in MDA. Examination of H₂O₂ and O₂-, the major ROS responsible for lipid peroxidation indicated that root tips challenged with Al in the presence of SA contained significantly lower contents of H₂O₂ and O₂- than those with Al alone. However, the reduced levels of H₂O₂ appeared not to be correlated with enhanced activities of ROS-scavenging enzymes like catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), but with increased activities of guaiacol peroxidase (POD). SA-induced reduction of H₂O₂ was also correlated with suppression of O₂- accumulation and superoxide dismutase (SOD) activities. From the results, it is concluded that SA might activate an H2O2-mediated pathway, which in turn initiated a POD-dependent antioxidative mechanism for retarding lipid peroxidation or preserving membrane integrity in root tips of C. tora. We presented the evidence of time-dependent changes in endogenous SA in root tips exposed to 20 mmol/L Al.

Key words: salicylic acid, aluminum, oxidative stress, hydrogen peroxide, Cassia tora