Effect of heavy metals on germination, biochemical, antioxidant and withanolide content in Withania somnifera (L.) Dunal

Withania somnifera (L.) Dunal., commonly referred to as Ashwagandha, is a medicinal plant from the solanaceae family with a wide range of pharmacological properties. W. somnifera is a rich source of withanolides, such as withanolide A, withanolide B, withanolide D, withaferin A, etc. and these molecules are attributed for large number of pharmacological activities. In the present study, the impact of heavy metals such as cadmium (Cd), mercury (Hg), and lead (Pb) has been assessed on the growth, biochemical parameters, antioxidant activity and withanolide A and withaferin A content of W. somnifera. The seeds of W. somnifera were germinated in cocopeat treated with different concentrations of Cd (0–200 ppm), Hg (10–100 ppm), and Pb (0–2000 ppm) for 21 days. There have been substantial differences between the heavy metal-treated plants and the control plants with the lowest germination of 20% has been observed in the plants treated with 2000 ppm Pb. The selected metals inhibited vegetative growth with lowest length of 3.07 cm and lowest biomass of 0.74 g in 180 ppm Cd and 200 ppm Cd treated plants respectively. With the addition of heavy metals, biochemical parameters like protein, carbohydrate, chlorophyll, total phenol, flavonoid, and proline content varied significantly and showed metal tolerance by exhibiting antioxidant activity at lower concentrations. The metal accumulation occurred in a dose-dependent manner with highest Cd accumulation of 14.30 mg kg?1, Hg accumulation of 42.45 mg kg?1, and Pb accumulation of 217.46 mg kg?1 of dry biomass of the plants. The withanolide content increased up to a specific metal concentration and decreased with a further increase in heavy metal concentration. The seeds treated with 1200 ppm of Pb showed the highest withanolide A content of 1.7 mg g?1 DW, and the seeds treated with 80 ppm of Cd showed the highest withaferin A content of 3.2 mg g?1 DW.