Scientia Horticulturae 140 (2012) 66–73 Contents lists available at SciVerse ScienceDirect Scientia Horticulturae journa l h o me page: www.elsevier.com/locate/scihorti Antioxidant defense system and proline accumulation enables hot pepper to perform better under drought Shakeel Ahmad Anjum a , Muhammad Farooq b,c,∗ , Xio-yu Xie a , Xio-jian Liu a , Muhammad Furqan Ijaz d a College of Agronomy and Biotechnology, Southwest University, Chongqing 400716, China b Department of Agronomy, University of Agriculture, Faisalabad 38040, Pakistan c The UWA Institute of Agriculture, The University of Western Australia, Crawley, WA 6009, Australia d Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad 38040, Pakistan a r t i c l e i n f o Article history: Received 13 December 2011 Received in revised form 23 March 2012 Accepted 27 March 2012 Keywords: Antioxidant enzymes Drought stress Lipid peroxidation Pepper Proline a b s t r a c t Water availability is the most critical factor, which limits the productive potential of plants. Plants adapt to water deficits by physiological alteration, biochemical changes and osmotic adjustments. The responses of two pepper (Capsicum annuum L.) cultivars (Shanshu-2001 and Nongchengjiao-2) were investigated to elucidate the leaf water status, osmolyte accumulation, membrane lipid peroxidation, and key protective antioxidant enzymes activity under varying levels of progressive drought stress. Pepper cultivars were submitted to four water supply regimes [80,60, 40 and 20% field capacity (FC)]; served as control, mild, moderate and severe water stress, respectively. Shanshu-2001 showed a higher relative leaf water con- tent (RLWC), protein, and proline accumulation than Nongchengjiao-2 in all water regimes during the course of experiment. Interestingly, total soluble proteins and proline continued to increase with progres- sion in drought in cultivar Shanshu-2001, whereas in cultivar Nongchengjiao-2 only proline continued to increase but with a lower rate than cultivar Shanshu-2001. Membrane lipid peroxidation and electrolyte leakage were increased with prolongation in drought, with higher rates in cultivar Nongchengjiao-2 than cultivar Shanshu-2001. The progression in drought enhanced the activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) initially, which were then decreased. Constitutive activities of SOD, POD, and CAT were higher in Shanshu-2001 than in Nongchengjiao-2, which resulted in improved growth and yield in Shanshu-2001. Overall the cultivar Shanshu-2001 was better able to resist drought as indicated by better growth and yield due to higher antioxidant enzymes, reduced lipid peroxidation, better accumulation of osmolytes and maintenance of tissue water contents. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Changing climate is mainly characterized by increase in emis- sion of green house gases, global mean temperature, and changes in precipitation levels and patterns (IPCC, 2007). Owing to changed patterns of precipitation, episodes of drought are increasing and are expected to increase in days to come (IPCC, 2007). It is thus imperative to make the plants ready for the water deficit or drought. However this all requires better understanding of the mechanism of resistance and adaptation to drought (Farooq et al., 2009a). Plants have evolved complex mechanisms to perceive, respond and adapt to water deficit. For instance, they can avoid drought by maximizing water uptake or minimizing water loss (Chaves ∗ Corresponding author at: Department of Agronomy, University of Agriculture, Faisalabad 38040, Pakistan. Tel.: +92 300 7108652; fax: +92 41 9200605. E-mail addresses: mfarooq@uaf.edu.pk, farooqcp@gmail.com (M. Farooq). et al., 2003) or accumulate some osmolytes to cope with the stress (Szira et al., 2008). These osmolytes accumulate in the cytosol and are not toxic even at higher concentrations (Reddy et al., 2004). Drought induces oxidative damage leading in the forma- tion of active and reactive oxygen species (Farooq et al., 2009a,b). Production of these species is started with reduction of O 2 lead- ing in the synthesis of singlet oxygen ( 1 O 2 ), superoxide (O 2 - ), hydroxyl radical (OH - ) or hydrogen peroxide (H 2 O 2 ) (Wu et al., 2008). Production of these species at higher level may damage cellular membranes and other vital substances like chlorophyll, DNA, proteins and lipids (Blokhina et al., 2003). Accumulation of osmolytes, such as proline, glycinebetaine, etc., helps in conserv- ing tissue water and protect the proteins and cellular membranes from the osmotic and oxidative stresses (Ashraf and Foolad, 2007; Farooq et al., 2009a,b). Improvement in the synthesis of these osmolytes has been found to improve resistance against drought in maize (Anjum et al., 2011a,b), rice (Farooq et al., 2008a), sunflower (Hussain et al., 2008); chilling in maize (Farooq et al., 2008b, 2009c), and heat in sugarcane (Rashid et al., 2011) and wheat (Farooq et al., 2011). 0304-4238/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2012.03.028