Effect of supplemental ultraviolet-B radiation on <em>Withania</em> <em>somnifera </em>L. (Dunal): An appraisal of morphological, physiological and biochemical characteristics

Abstract

<em>Withania somnifera </em> L. (Dunal), commonly called Indian Ginseng or Ashwagandha, is an indigenous medicinal plant and has been a source of numerous pharmacological compounds for centuries, and ultraviolet-B (UV-B) radiation is one of the potent factors capable of influencing the plant’s performance, consequently influencing its medicinal properties. UV-B studies on medicinal plants are scarce, especially with respect to the overall plant performance. In the present study, we subjected <em>W</em>.<em> somnifera</em> to supplemental UV-B (s-UV-B) radiation (+3.6 kJ m^-2 day^-1) above ambient to study its morphological, physiological, and biochemical characteristics at three sampling ages (40, 70 and 100 days after transplantation). All growth characteristics, except root length, reduced under s-UV-B treatment. Physiological parameters, such as photosynthetic rate (P_s), stomatal conductance (g_s) and water use efficiency (WUE) decreased under s-UV-B while internal CO₂(C_i) increased. Quantum yield (F_v/F_m) also recorded a decline at all sampling ages. Protein and chlorophyll contents decreased while phenolics and antioxidants (ascorbic acid, α-tocopherol and thiols) increased in exposed leaves and roots. IAA oxidase activity also increased in both plant parts at all ages. The study concludes that s-UV-B stress is a potent factor in increasing the concentrations of defence compounds and antioxidants to optimise the plant performance under this stress.