Arsenic Toxicity Induced Changes in Growth, Photosynthetic Pigments, Antioxidant Machinery, Essential Oil, Menthol and Other Active Constituents of Menthol Mint (Mentha arvensis L.)

The present investigation was premeditated to explore the toxic effects of arsenic (As) on an essential oil-bearing plant, the menthol mint (Mentha arvensis L.). Arsenic was applied in the form of sodium arsenate (Na2HAsO4.7H2O) to the soil. Different concentrations of As (20, 40, 60, 80, and 100 mg kg-1of soil) were applied and one set of plants was kept as control. The response of plants towards As exposure was in a dose dependent order. Soil-applied As showed negative effects on the growth and physiological performance of plants. The chlorophyll, carotenoids content and chlorophyll fluorescence were significantly decreased by the As treatment ranging from 20 to 100 mg kg-1 of soil, however, maximum reduction was observed at the highest applied As concentration of 100 mg kg-1 of soil. The level of antioxidants whether enzymatic (superoxide dismutase, peroxidase) or non-enzymatic (proline) were enhanced by increasing the concentration of As to the plants with a slight decrease in activity of catalase (CAT) beyond 60 mg As kg-1of soil. The content of essential oil (EO) was significantly decreased at the highest concentration (100 mg As kg-1 of soil), but a slight increase in EO content was observed at 20 mg As kg-1 of soil. GC-MS analysis revealed the percentage of EO active components of the crop. The main constituent (menthol content) of the EO was also reduced at the maximum concentration of As. Interestingly; contents of menthyl acetate and menthone were enhanced in a dose dependent manner. Thus, the present study illustrates that the highest concentration of As proved toxic for mint crop.