ORIGINAL ARTICLE Physiological performance, secondary metabolite and expression profiling of genes associated with drought tolerance in Withania somnifera Sanchita & Ruchi Singh & Anand Mishra & Sunita S. Dhawan & Pramod A. Shirke & Madan M. Gupta & Ashok Sharma Received: 24 November 2014 /Accepted: 26 January 2015 # Springer-Verlag Wien 2015 Abstract Physiological, biochemical, and gene expression responses under drought stress were studied in Withania somnifera. Photosynthesis rate, stomatal conductance, transpi- ration rate, relative water content, chlorophyll content, and quantum yield of photosystems I and II (PSI and PSII) de- creased in response to drought stress. Comparative expression of genes involved in osmoregulation, detoxification, signal transduction, metabolism, and transcription factor was ana- lyzed through quantitative RT–PCR. The genes encoding 1-pyrroline-5-carboxylate synthetase (P5CS), glutathione S-transferase (GST), superoxide dismutase (SOD), serine threonine-protein kinase (STK), serine threonine protein phosphatase (PSP), aldehyde dehydrogenase (AD), leucoanthocyanidin dioxygenase/anthocyanin synthase (LD/AS), HSP, MYB, and WRKY have shown upregu- lation in response to drought stress condition in leaf tissues. Enhanced detoxification and osmoregulation along with in- creased withanolides production were also observed under drought stress. The results of this study will be helpful in developing stress-tolerant and high secondary metabolite yielding genotypes. Keywords Withanolides . Water stress . Withania somnifera . Gene expression . Photosynthesis rate Introduction Withania somnifera (Ashwagandha) is an important medicinal plant of Indian origin. The plant is well known to be effective in immunomodulation, hematopoiesis, anti-aging, chronic stress, cardiovascular protection, hypothyroidism, anxiety, and depression (Verma and Kumar 2011). Secondary metab- olites play an important role in plants for adaptation and de- fense against adverse environmental conditions (Ramakrishna and Ravishankar 2011). These metabolites are useful for humans as pharmaceutical agents. Withanolides are a class of secondary metabolites synthesized in W. somnifera. Withanolide biosynthesis starts with Acetyl Co A, a byproduct of glycolysis, followed by terpenoid and steroid biosynthetic pathways. Generally, secondary metabolite content increases under stress conditions in plants. Drought stress generates reactive oxygen species (ROS) such as singlet oxygen, su- peroxide anion radicals, hydroxyl ions, and hydrogen peroxide (Cruz de Carvalho 2008). These ROS are con- sidered as markers of initiation of stress, serving as signal- ing molecules to activate the cell response against stress (Shulaev and Oliver 2006). Osmolytes are organic molecules of low molecular weight which play a prominent role as osmoprotectant. The osmolytes such as glycine betaine and proline accumulate in cells and balance the osmotic difference between cytosol and surrounding of the cell. The accumula- tion of these molecules results in the enhancement of stress tolerance (Agarwal et al. 2013). The leaf and soil water con- tent decreases with the increase in drought stress. Due to loss of relative water content (RWC), leaves lose their turgidity and stomata get closed. CO 2 concentration decreases in Handling Editor: Bhumi Nath Tripathi Sanchita : A. Mishra : S. S. Dhawan : A. Sharma (*) Biotechnology Division, CSIR–Central Institute of Medicinal and Aromatic Plants, Lucknow, India e-mail: ashoksharma@cimap.res.in R. Singh : P. A. Shirke Plant Physiology Division, CSIR–National Botanical Research Institute, Lucknow, India M. M. Gupta Chemical Sciences Division, CSIR–Central Institute of Medicinal and Aromatic Plants, Lucknow, India Protoplasma DOI 10.1007/s00709-015-0771-z