Effect of selenium foliar spray on physiological and biochemical processes and chemical constituents of wheat under drought stress Fahim Nawaz a,n , R. Ahmad a , M.Y. Ashraf b , E.A. Waraich a , S.Z. Khan c a Department of Crop Physiology, University of Agriculture, Faisalabad, Pakistan b Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan c Department of Entomology, University of Agriculture, Faisalabad, Pakistan article info Article history: Received 3 June 2014 Received in revised form 13 November 2014 Accepted 1 December 2014 Available online 11 December 2014 Keywords: Foliar spray Se Drought stress Nutrients contents Antioxidants Wheat abstract Selenium (Se) is considered an essential micronutrient for humans, animals and plants due to its phy- siological and antioxidative properties. The positive role of Se in attenuation of drastic effects of various environmental stresses in plants is, however, still unclear and need to be explored. The present study aimed at investigating the physiological and biochemical changes induced by Se foliar spray to improve the drought tolerance potential of wheat. Additionally, we also examined the effect of supplemental Se on uptake of nutrients using detection by ICP-OES. Foliar Se application significantly lowered osmotic potential (13%) that markedly improved turgor by 63%, enhanced transpiration rate (60%), improved accumulation of total soluble sugars (33%) and free amino acids (118%) and activity of antioxidant system which ultimately increased the grain yield by 24%. Supplemental Se also significantly increased Se contents (5.77 mgg À1 DW) and improved Fe (91%) and Na (16%) uptake, whereas it reduced Zn accu- mulation by 54% and did not affect Ca contents. The results supported our hypothesis that supplemental Se influences nutrients uptake and wheat yield through maintenance of turgor and gas exchange char- acteristics and enhancement in antioxidant system activity. & 2014 Elsevier Inc. All rights reserved. 1. Introduction Drought stress is one of the major limitations to agricultural productivity around the globe (Waraich et al., 2011). The identifi- cation of strategies to improve plant productivity under limited water conditions is a big challenge for plant scientists. The arid and semi-arid regions of the world, especially in the developing countries, are at greater risk because these regions are already facing acute shortage of water. Furthermore, an increasing fre- quency of droughts in days ahead will make natural and cultivated vegetation more vulnerable to severe and acute shortage of water (Nawaz et al., 2012). Wheat is a major food grain crop of the world. Hence it is necessary to develop better drought mitigation stra- tegies, with the ultimate goal of increasing drought tolerance po- tential and wheat yield to meet the demands of ever growing world's population. The physiological and antioxidative properties of selenium (Se) have raised the curiosity of biologists in recent past. It plays beneficial role in plants by enhancing growth of plants (Cartes et al., 2010), reducing damage caused by UV-induced oxidative stress (Yao et al., 2013), increasing chlorophyll and carotenoids in plant leaves (Dong et al., 2013), stimulating enzymatic and non- enzymatic antioxidant system against Cd-toxicity (Kumar et al., 2012; Lin et al., 2012) and improving plant tolerance to drought stress by regulating water status (Yao et al., 2009). Low levels of Se stimulate the antioxidant machinery in plants but it acts as a prooxidant at high levels (Feng et al., 2013). The increase in acidity, iron oxides/hydroxides, organic matter and high clay content of soil (Mikkelsen et al., 1989; Kabata-Pen- dias, 2001) decreases the effectiveness and bioavailability of Se to plants. The soil moisture also affects the availability of Se as it is more available under low precipitation conditions (Zhao et al., 2007). The foliar application of Se can be used as an alternative for enrichment of agricultural products with Se (Smrkolj et al., 2006) because it minimizes the impact of soil chemistry and micro- biology on Se uptake and accumulation, hence improving efficacy even with low volumes of foliar applied Se solution (Kapolna et al., 2012). Furthermore, the actively growing tissues usually contain large amounts of Se (Kahakachchi et al., 2004) and accumulation is higher in shoot than in root tissues (Zayed et al., 1998). Hence Se foliar spray is much more viable and effective approach than soil application to improve Se content in plants (Kapolna et al., 2009). Foliar Se application facilitates Se transport through xylem and Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety http://dx.doi.org/10.1016/j.ecoenv.2014.12.003 0147-6513/& 2014 Elsevier Inc. All rights reserved. n Corresponding author. Present address: Department of Plant Sciences, Uni- versity of Oxford OX1 3RB, United Kingdom. E-mail addresses: fahim5382@gmail.com, fahim.nawaz@plants.ox.ac.uk (F. Nawaz). Ecotoxicology and Environmental Safety 113 (2015) 191–200