Arsenite and arsenate impact the oxidative status and antioxidant responses in Ocimum tenuiflorum L.

Biochemical responses of Ocimum tenuiflorum plants were studied upon exposure to arsenite (AsIII) and arsenate (AsV) for 1 to 10 d. Plants accumulated significant amounts of As in leaves (662 µg g(-1) dry weight; DW and 412 µg g(-1) DW in response to 100 µM AsIII and AsV exposure, respectively after 10 d). Consequently, fresh weight and growth of plants declined in a concentration dependent manner. Further, total chlorophyll and carotenoid contents also declined while oxidative stress markers increased, particularly on longer durations. Various antioxidant enzymes and thiols (cysteine and glutathione; GSH) showed significant and variable increases upon exposure to AsV and AsIII with the response being comparatively better in response to AsV. Proline increased significantly upon exposure to both AsIII and AsV. Plants thus tolerated high As concentrations through induced antioxidant machinery.

Analysis of arsenic induced physiological and biochemical responses in a medicinal plant, Withania somnifera.

Withania somnifera has been an important herb in the Ayurvedic and indigenous medical systems for centuries in India. However, these grow as weeds mostly in the wastelands, which receive contaminated water from municipal and industrial sources. In the present investigation, plants of Withania somnifera were exposed to various concentrations of arsenate (AsV) and arsenite (AsIII) (0, 10, 25, 50, 100 µM) for 10 days and analysed for accumulation of arsenic (As) and physiological and biochemical changes. Plants showed more As accumulation upon exposure to AsIII (320 µg g(-1) DW in roots and 161 µg g(-1) DW in leaves) than to AsV (173 µg g(-1) DW in roots and 100 µg g(-1) DW in leaves) after 10 days of treatment. Consequently, AsIII exposure caused more toxicity to plants as compared to that AsV, as evaluated in terms of the level of photosynthetic pigments and oxidative stress parameters (superoxide, hydrogen peroxide and lipid peroxidation), particularly at higher concentrations and on longer durations. Plants could tolerate low concentrations (variable for AsIII and AsV) until longer durations (10 days) and high concentrations for shorter durations (1-5 days) through increase in antioxidant enzymes and by augmented synthesis of thiols. In conclusion, As tolerance potential of Withania plants on one hand advocates its prospective use for remediation under proper supervision and on the other demonstrates possible threat of As entry into humans due to medicinal uses.