Amelioration of cadmium stress in Withania somnifera by ROS management: active participation of primary and secondary metabolism

Cadmium (Cd) isconsidered as a non-essential heavy metal with substantial toxicity on environment. Withania somnifera, a reputed therapeutic herb exhibitsvast pharmacological activities due to the presence of steroidal lactones-withanolides. The present study deals with reactive oxygen species (ROS) management through primary and secondary metabolism as adaptive response, on exogenous Cd exposure of W. somnifera. Increased invertase enzyme activity resulted in higher reducing sugars in plant under Cd stress to provide additional carbon source and NADH or NADPH. Higher activities of proline metabolic pathway enzymes such as ornithine aminotransferase (OAT) and pyrroline-5-corboxylate synthase (P5CS) resulted in elevated proline accumulation. The considerable participation of phenylpropanoid metabolism also found dominantly upregulated. Increased enzyme activities of phenylalanine ammonia lyase (PAL), shikimate dehydrogenase (SKDH), glucose-6-phosphate dehydrogenase (G6PDH), and cinnamyl alcohol dehydrogenase (CADH) resulted in phenolics and flavonoids accumulation under higher Cd stress. Upregulation of glutathione-S-transferase (GST) activity conferred its role in Cd chelation. In addition, glutamate oxaloacetate transaminase (GOT), amyl esterase (EST) and diaphorase (DIA) established their participation in Cd tolerance mechanism. Thus, present study elucidated major role of proline and phenylpropanoid metabolism in providing the osmoticum and antioxidants to the plants under Cd stress. The information may be helpful in developing stress resistant plants by targeting these pathways using conventional and molecular approaches.