Elucidation of zinc and copper induced oxidative stress, DNA damage and activation of defence system during seed germination in Cassia angustifolia Vahl

• High accumulation of Zn and Cu in roots of C. angustifolia.
• Zn and Cu induced small molecular weight proteins at higher concentration of metals.
• Increased DNA damage due to heavy metal stress.
• Zn and Cu stress led to high accumulation of proline.
• C. angustifolia can be utilized as a model plant for phytoremediation study.

Investigations conducted on Cassia angustifolia to see the effect of zinc (Zn) and copper (Cu) during seed germination, revealed drastic toxicity on seedling growth, alteration in antioxidant enzymes, morphological changes and metal accumulation in various plant parts. Seeds were germinated on Knop’s medium containing Zn and Cu individually in various concentrations (0, 1, 10, 50, 100 and 200 mg L−1). Decline in seed germination initiated above 1 mg L−1 and maximum inhibition was seen at 200 mg L−1 where it was 40 and 25.0%, respectively under Zn and Cu over control (67.67%). Average shoot length decreased from 5.53 cm (control) to 2.1 and 1.4 cm whereas average root length decreased from 7.12 cm (control) to 1.5 and 0.3 cm under Zn and Cu, respectively. Atomic absorption spectroscopy revealed that maximum Zn and Cu (1682.48 and 9516.99 mg kg−1 dry weight, respectively) were stored in roots. Superoxide dismutase activity increased up to 2.71 and 3.27 fold at 200 mg L−1 Zn and Cu, respectively. Catalase, ascorbate peroxidase, guaiacol peroxidase and glutathione reductase followed similar trend. Malondialdehyde and proline content accounted for 52.7 μmol mg−1 and 10.0 μmol g−1 fresh weight, respectively in control seedlings. Malondialdehyde increased up to 2.5 and 3.33 fold and proline up to 9.42 and 11.20 fold at 200 mg L−1 Zn and Cu, respectively. Comet assay revealed extensive DNA damage at higher concentration and protein analysis showed various low molecular weight proteins (20–14 kDa) at higher concentration. This is our first report of in vitro heavy metal stress study on C. angustifolia. Induction of anti-oxidative response and proline accumulation suggests the tolerance strategy adopted by C. angustifolia and its high metal accumulation potential can be utilized in phytoremediation.