Salicylic acid pre-treatment modulates Pb 2+ -induced DNA damage vis-à-vis oxidative stress in Allium cepa roots.

The current study investigated the putative role of salicylic acid (SA) in modulating Pb ²⁺ -induced DNA and oxidative damage in Allium cepa roots. Pb ²⁺ exposure enhanced free radical generation and reduced DNA integrity and antioxidant machinery after 24 h; however, SA pre-treatment (for 24 h) ameliorated Pb ²⁺ toxicity. Pb ²⁺ exposure led to an increase in malondialdehyde (MDA) and hydrogen peroxide (H ₂ O ₂ ) accumulation and enhanced superoxide radical and hydroxyl radical levels. SA improved the efficiency of enzymatic antioxidants (ascorbate and guaiacol peroxidases [APX, GPX], superoxide dismutases [SOD], and catalases [CAT]) at 50-μM Pb ²⁺  concentration. However, SA pre-treatment could not improve the efficiency of CAT and APX at 500 μM of Pb ²⁺ treatment. Elevated levels of ascorbate and glutathione were observed in A. cepa roots pre-treated with SA and exposed to 50 μM Pb ²⁺ treatment, except for oxidized glutathione. Nuclear membrane integrity test demonstrated the ameliorating effect of SA by reducing the number of dark blue-stained nuclei as compared to Pb ²⁺ alone treatments. SA was successful in reducing DNA damage in cell exposed to higher concentration of Pb ²⁺ (500 μM) as observed through comet assay. The study concludes that SA played a major role in enhancing defense mechanism and protecting against DNA damage by acclimatizing the plant to Pb ²⁺ -induced toxicity.
(© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)