Salicylic acid pre-treatment modulates Pb-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-induced DNA and oxidative damage in Allium cepa roots. Pb exposure enhanced free radical generation and reduced DNA integrity and antioxidant machinery after 24 h; however, SA pre-treatment (for 24 h) ameliorated Pb toxicity. Pb exposure led to an increase in malondialdehyde (MDA) and hydrogen peroxide (HO) 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 Pbconcentration. However, SA pre-treatment could not improve the efficiency of CAT and APX at 500 μM of Pb treatment. Elevated levels of ascorbate and glutathione were observed in A. cepa roots pre-treated with SA and exposed to 50 μM Pb 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 alone treatments. SA was successful in reducing DNA damage in cell exposed to higher concentration of Pb (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-induced toxicity.