Effects of Exogenous Silicon on Cadmium Accumulation and Biological Responses of Nigella sativa L. (Black Cumin)

Medicinal plants are an age-old source of therapeutic agents to cure human disease. Nigella sativa is used for edible and medicinal purposes in many countries. In this study, biochemical and physiological responses of N. sativa to cadmium (Cd) toxicity were investigated. Experiments were performed to study individual and combined effects of exogenous silicon (Si) applied at 60, 120, and 180 mM in the form of sodium silicate nonahydrate (Na₂SiO₃•9H₂O) on Cd phytotoxicity in plants grown in perlite containing different concentrations of cadmium nitrate (CdN₂O₆). Cadmium treatment (120 μM) decreased chlorophyll and carotenoid content, dry weight, relative water content, and root and shoot fresh weights compared with the control while proline content and lipid peroxidation increased relative to the control. Black cumin is able to accumulate Cd, but Si is also able to mitigate the negative consequences on growth and yield parameters.