BIOLOGIA PLANTARUM 58 (2): 328-334, 2014 DOI: 10.1007/s10535-014-0390-0 328 Effect of ultraviolet-B radiation on biomass production, lipid peroxidation, reactive oxygen species, and antioxidants in Withania somnifera S. TAKSHAK and S.B. AGRAWAL* Laboratory of Air Pollution and Global Climate Change, Department of Botany, Banaras Hindu University, Varanasi-221005, India Abstract The present study was aimed at understanding the effects of long term supplemental UV-B (3.6 kJ m -2 d -1 ) on biomass production, accumulation of reactive oxygen species, lipid peroxidation, and enzymatic antioxidants in leaves and roots of Withania somnifera (an indigenous medicinal plant). Under the UV-B treatment, a reduction in biomass and an increased malondialdehyde content (a characteristic of lipid peroxidation) were observed in both the shoots and roots. Amongst ROS, H 2 O 2 content increased under UV-B in the leaves, whereas it decreased in the roots, and superoxide radical production rate decreased in both the plant parts. The activities of all enzymatic antioxidants tested (ascorbate peroxidase, catalase, glutathione reductase, peroxidase, polyphenol oxidase, and superoxide dismutase) increased under the UV-B treatment, the increase being greater in the roots. Additional key words: ascorbate peroxidase, catalase, glutathione reductase, malondialdehyde, oxidative stress, peroxidase, polyphenol oxidase, superoxide dismutase. Introduction Ultraviolet radiation is an abiotic factor which influences various aspects of plant life (Ballaré et al. 2011, McKenzie et al. 2011) and its effects are highly variable (Krupa and Kickert 1989, Jordan 1996). Plants respond to UV radiation via expression of specific genes involved in plant growth, development, and secondary metabolism. Production of biomass, as one of the key parameters, has been studied extensively under UV-B stress (Kumari et al. 2009a,b, Ravindran et al. 2010). Another definitive response of plants to UV-B exposure is the generation of reactive oxygen species (ROS) like singlet oxygen ( 1 O 2 ), superoxide radical (˙O 2 - ), H 2 O 2 , and hydroxyl radical (˙OH). Their over-accumulations can result in cell death (Mackerness et al. 2001). To counteract their damaging effects, plants produce ROS scavengers in the form of enzymatic and non-enzymatic antioxidants (Agrawal et al. 2009). The former include various enzymes like superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), catalase (CAT), peroxidase (POX), and polyphenol oxidase (PPO) among others (Mittler et al. 2004). Fig. 1 summarises some of the effects of UV-B on plant membranes and consequent plant responses. Withania somnifera (Solanaceae) is a medicinal plant used for centuries. Its medicinal properties are primarily attributed to withanolides present in its roots (Sharma et al. 2011). The effect of UV-B radiation on ROS production and antioxidants is not known in this species. Thus, the present study was aimed at investigating the effect of supplemental UV-B radiation on biomass production, ROS (H 2 O 2 and ˙O 2 - ), and enzymatic antioxidants (APX, CAT, GR, POX, PPO, and SOD) in the leaves and roots of the W. somnifera in order to evaluate the significance of the antioxidant systems in conferring tolerance of this plant to UV-B stress.  Submitted 24 May 2013, last revision 5 August 2013, accepted 30 September 2013. Abbreviations: APX - ascorbate peroxidase; CAT - catalase; DAT - days after transplantation; GR - glutathione reductase; ˙OH - hydroxyl radical; H 2 O 2 - hydrogen peroxide; LPO - lipid peroxidation; MDA - malondialdehyde; ˙O 2 - - superoxide radical; POX - peroxidase; PPO - polyphenol oxidase; ROS - reactive oxygen species; SOD - superoxide dismutase; TBA - thiobarbituric acid; TCA - trichloroacetic acid; UV-B - ultraviolet B radiation; UV-B BE - biologically effective UV-B. Acknowledgement: The authors are thankful to the Head, Department of Botany, Banaras Hindu University, for providing laboratory facilities, and to the University Grants Commission (UGC), New Delhi, for financial assistance. * Corresponding author, fax: (+91) 542 2368174, e-mail: sbagrawal56@gmail.com