Physiological and genotoxic responses of Zinnia elegans Jacq. under chromium exposure for phytoremediation

Zinnia elegans Jacq., a hardy ornamental species, was evaluated for its phytoremediation potential in chromium (Cr) contaminated soils from Sukinda chromite mining region of Odisha, India one of the world’s most polluted mining sites due to the leaching of toxic Cr(VI) into surrounding ecosystem. A pot culture experiment was established using graded concentrations of chromium-rich overburden soil (OBS; 20–100%) in a completely randomized strip-plot design. Certified seeds were surface-sterilized, and cytological effects were assessed using OBS-ddH2O suspensions (0–80%) through root-tip mitotic preparations. Growth, biochemical constituents, oxidative stress markers, and antioxidant enzymes (catalase, glutathione peroxidase, ascorbate peroxidase) were quantified at 30, 45, and 60 days using standard spectrophotometric assays. Chromium accumulation in plant tissues was used to determine bio-concentration factor (BCF), translocation factor (TF), and tolerance index (TI). Low Cr levels (20% OBS) improved growth, biomass, flowering, and biochemical attributes, whereas higher concentrations induced substantial morphological and physiological inhibition. Elevated Cr exposure significantly reduced mitotic index (M.I.) and increased chromosomal aberrations, indicating strong genotoxic stress. Oxidative damage intensified with increasing Cr, reflected by higher malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels, alongside enhanced antioxidant enzyme activities. Chromium accumulation was highest in roots, with increasing TF and declining BCF and TI at higher OBS levels, suggesting restricted upward translocation as a tolerance mechanism. Overall, the study demonstrates that Z. elegans tolerates and accumulates Cr while activating strong antioxidant and cytoprotective responses, highlighting its potential as a non-edible phytoremediation species for rehabilitating heavily contaminated areas such as Sukinda.