Effect of chromium accumulation on photosynthetic pigments, oxidative stress defense system, nitrate reduction, proline level and eugenol content of Ocimum tenuiflorum L

Ocimum tenuiflorum L. exposed to various concentrations of chromium (0.0, 10.0, 20.0, 50.0, 100.0 μM) accumulated high amount of chromium in various plant parts in a concentration and duration dependent manner. Chromium induced lipid peroxidation coupled with potassium leakage. Toxic effects of chromium on O. tenuiflorum were reflected by the reductions in photosynthetic pigments, protein, cysteine, ascorbic acid and non-protein thiol contents. In addition, chromium toxicity resulted in the reduction of nitrate reductase activity through impaired substrate utilization. However, chromium treated O. tenuiflorum leaves showed increased proline content. Hyperactivity of the superoxide dismutase (SOD), guaiacol peroxidase (GPX) and catalase indicated that antioxidant enzymes played an important role in protecting the plant from chromium toxicity. However, APX took a little part in detoxification of H 2O 2 due to its sensitivity to chromium. Therefore, reduced ascorbate peroxidase activity in chromium treated O. tenuiflorum plants was recorded. This reflects the sensitivity of the enzyme to the chromium. Further, chromium treated plants yielded more eugenol (a major component of Ocimum essential oil) in comparison to the control (14.46, 24.61, 16.80, 3.83% more eugenol from 10, 20, 50 and 100 μM chromium exposed plants, respectively). The study concludes that plant could grow under chromium stress and protect themselves from phytotoxicity of Cr by altering various metabolic processes. Further, the use of leaves collected from chromium polluted habitat in medicinal preparation is not safe for human health due to high chromium contents.