Cold stress affects antioxidative response and accumulation of medicinally important withanolides in Withania somnifera (L.) Dunal

Abstract

Withania somnifera (L.) Dunal (Indian ginseng) is a high value medicinal plant. It synthesizes a large array of biologically active withanolides. In this study, two month old seedlings of AGB002 (wild genotype) and AGB025 (cultivated genotype) of W. somnifera were subjected to cold stress (4°C) under controlled environment. Plants were analyzed for three medicinally important secondary metabolites (withanolide A, withanone and withaferin A), lipid peroxidation (MDA), cell injury, superoxide radical (O2−) accumulation and anti-oxidative enzymes activities such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR). Increases in the titers of superoxide anion and MDA were observed from day 1 to day 7 in both genotypes, although the increase on the first day of exposure was significantly higher. Enzymatic activities of SOD, CAT, APX and GR also showed an increasing trend in both genotypes and reached a maximum on day 7 of the cold temperature exposure; however, this increase was higher in AGB002 than AGB025. Withanolide A (WS-1) in the roots of both genotypes significantly decreased on the first day of cold exposure and then showed a recovery until day 7. WS-1 was not detected in the leaves of either genotype. Withanone (WS-2) content in the leaves also decreased towards the end of the cold period in both genotypes. Cold stress also elicited the accumulation of WS-2 in AGB025, but was not detectable in control seedlings. At maturity, WS-2 was also detected in control plants. Furthermore, a significant increase in the leaf withaferin A (WS-3) content was recorded from day 1 to day 7 of the cold exposure in both the genotypes, suggesting the possible involvement of withanolides in cold-protection. AGB002 showed comparatively higher accumulation of antioxidant enzymes and selected marker withanolides than AGB025, indicating that AGB002 is better adapted to cold than AGB025. It could be inferred from these observations that cold stress induces bioactive withanolide accumulation in W. somnifera as a mechanism for scavenging reactive oxygen species (ROS). These studies also provide an impetus for enhancing the withanolide accumulation in W. somnifera using controlled environment technology.