Physiological performance, secondary metabolite profiling and photo oxidative tolerance in Withania somnifera

Withania somnifera (L.) Dunal is a high value medicinal plant. It synthesizes a large array of biologically active withanolides. The impact of photoperiod on morphological, physiological, biochemical parameters and neuroactive constituent with anolides has been studied. In light treatments (blue light) one month old plants were exposed to different light regimes (8 h, 12 h, 16 h, 20 h and 24 h) with constant at 22 h with light intensity of 55 μmol. The light treatments significantly decreased stem length, root length, fresh weight and dry weight in all the treatments except 8 h and 12 h photoperiods, where there was marginal increase in stem length due to etiolation effect. Changes in leaf area, membrane stability and relative water content was also observed and decreased with stress. Total carbohydrates, protein, carotenoids, tocopherol, ascorbic acid and alkaloids were decreased. The antioxidant enzymes like superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione-S-transferase, DPPH (1, 1-diphenyl-2-picrylhydrazyl) and ABTS (2, 2’-azino-bis-3ethyl benzthiazoline-6-sulphonic acid) enhanced due to stress treatments. Withanolides were found to be higher in long photoperiod treated plants. W. somnifera was found to have protective defence mechanism against oxidative damage by maintaining higher enzymatic and non-enzymatic antioxidants.