Plant Archives Volume 20 No. 2, 2020 pp. 8535-8545 e-ISSN:2581-6063 (online), ISSN:0972-5210 AMELIORATING EFFECT OF PROLINE IN VITRO ON PHYSIOLOGICAL AND SECONDARY METABOLITE ANALYSIS OF SILYBUM MARIANUM L. GROWN UNDER ABIOTIC STRESS CONDITION (WATER DEFICIT STRESS) Somvir Singh*, Shalini Jaswal, Rahul Bhatia, Vishav Kiran, Sakshi Gupta, Priyanka Ratwan, Vandna Devi, Arti Thakur and Sunil Puri School of Biological and Environmental Sciences, Faculty of Sciences, Shoolini University of Biotechnology and Management Sciences, Solan (Himachal Pradesh), India. Abstract Physiological and secondary metabolite profile of Silybum marianum L. grown in hydroponic cultures in controlled condition of light (PAR: 40µmol m -2 s -1 ) and temperature (25±2ºc) evaluated to recognize the ameliorative role of proline against the negative effects of water deficit stress. Physiological analysis (carbohydrate, protein, proline, relative water content, chlorophyll) and secondary metabolite profile (phenol, flavonoid, alkaloid, saponin and glycosides) were determined after 45 days. Exogenous application of proline 50µg/l, 100µg/l and 150µg/l were standardized and applied to different PEG-6000 concentration 0.2, 0.4, 0.6, 0.8 and 1% in hydroponic solution. Proline enhanced the physiological and secondary metabolites in stressed plant; it is play a major role in cellular osmotic adjustment. Proline in stressed plants may have a significant role in osmotic adjustment. It could concluded that the addition of proline can ameliorate the oxidative stress in Silybum marianum L. stressed plants. This study also provided evidence for the ability of Silybum marianum L. plants grown in water deficit condition due to its capacity for osmotic adjustment. Key words: Abiotic Stress, Antioxidant, Medicinal Plants, Proline, Water Deficit Stress Introduction Silybum marianum L. is an annual medicinal plant belonging to the Asteraceae family. It also known as milk thistle and native to Southern Europe. In India, Western Himalayas and Kashmir are its natural habitat. Its medicinal effects documented among the alternative medicines referred to as liver and bile- related diseases remedy (Fraschini et al., 2002; Kurkin, 2003). Milk thistle oil has suggested for suitable edible oil and a vitamin E rich source it contains a phenolic compound known as silibinin, which is a major constituent of silymarin an extract of milk thistle seeds. (El- Mallah et al., 2003). Abiotic stresses such as high temperature, freezing/cold, drought/water, salinity, heavy metals, UV radiation and nutrient stresses have adverse effects on the physiology, biochemistry, molecular mechanisms, and survival of plants (Atkinson and Urwin 2012; Jeandroz and Lamotte 2017). In the scenario of global climatic change, different biotic and abiotic stresses are severe threats to the agricultural production worldwide. In nature, plants continuously stressed by exposure to multiple adverse conditions. Reactive oxygen species due to unfavorable environmental conditions such as drought, salinity, heavy metals, herbicides, nutrient deficiency, or radiation. Abiotic stress also lead to oxidative stress in the plant cell resulting in a higher leakage of electrons towards O 2 during photosynthetic and respiratory processes, which cause enhancement of reactive oxygen species (ROS) generation. Several ROS continuously produced in plants as byproducts of many metabolic reactions such as photosynthesis, photorespiration and respiration. Depending on the nature of the ROS, some are highly toxic and rapidly detoxified by various cellular enzymatic and non-enzymatic mechanisms. Abiotic stresses especially drought has the greatest effect on medicinal plants and do not generally adapt quickly to these stresses. *Author for correspondence : E-mail : somvirsingh@shooliniuniversity.com Water stress may arise either due to excess of water