Accumulation efficiency, genotoxicity and antioxidant defense mechanisms in medicinal plant Acalypha indica L. under lead stress

- Hyperaccumulation of Pb by Acalypha indica was not affected up to 500 mg L-l exposure.
- Pb exposure increased superoxide dismutase activity in both the leaf and root tissues.
- High levels of antioxidative defense enzymes evidenced the detoxification strategy.
- DNA changes showed the activation of molecular mechanism due to Pb genotoxicity.

The present study was designed to assess the physiological and biochemical changes in roots and shoots of the herb Acalypha indica grown under hydroponic conditions during exposure to lead (Pb) (100-500 mg L−1) for 1-12 d. The accumulation of Pb by A. indica plants was found to be 121.6 and 17.5 mg g−1 dry weight (DW) in roots and shoots, respectively, when exposed to a Pb concentration of 500 mg L−1. The presence of Pb ions in stem, root and leaf tissues was confirmed by scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX) analyses. Concerning the activity of antioxidant enzymes, viz., peroxidase (POX) catalase (CAT) and ascorbate peroxidase (APX), they were induced at various regimes during 5, 8 and 12 d of Pb exposure in both the leaves and roots than untreated controls. Lead treatment increased superoxide dismutase (SOD) activity in both the leaf and root tissues over control, irrespective of the duration of exposure. Anew, it was observed that Pb treatments induced variations in the number and intensity of protein bands. Random amplified polymorphic DNA (RAPD) results show that the Pb treatment caused genotoxicity on DNA molecules as evidenced by the amplification of new bands and the absence of normal DNA amplicons in treated plants. Results confirm that A. indica is a Pb accumulator species, and the antioxidants might play a crucial role in the detoxification of Pb-induced toxic effects.

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