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

Abstract

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 and many others which are attributed for a 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 and treated with different concentrations of Cd (20-200 ppm), Hg (10-100 ppm) and Pb (200-2000 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% observed in the plants treated with 2000 ppm Pb. The selected metals inhibited vegetative growth with lowest length of 3.07cm and lowest biomass of 0.74g 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 14.30mg kg−1, Hg accumulation of 42.45mg kg−1, and Pb accumulation of 217.46mg 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 1.7mg g−1 dry weight (DW), and the seeds treated with 80 ppm of Cd showed the highest withaferin A content of 3.2mg g−1 DW.