Antioxidant defense system and proline accumulation enables hot pepper to perform better under drought

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 content (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 progression 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. (C) 2012 Elsevier B.V. All rights reserved.