om www.scholarsresearchlibrary.c t Available online a Scholars Research Library Annals of Biological Research, 2015, 6 (11):39-46 (http://scholarsresearchlibrary.com/archive.html) ISSN 0976-1233 CODEN (USA): ABRNBW 39 Scholars Research Library Germination and antioxidant defense system in onion (Allium cepa. L) cultivars under salt stress Sai Sudha Gunisetty and Riazunnisa Khateef * Department of Biotechnology and Bioinformatics, Yogi Vemana University, Kadapa, Andhra Pradesh, India _____________________________________________________________________________________________ ABSTRACT Salinity is one of the major environmental aspects, which affects on plant growth, development and productivity of the agricultural crops worldwide. The aim of this study was to evaluate germination, initial growth parameters, antioxidant enzyme (CAT, APX and GR) activities and proline accumulation, Na + / K + content in seedlings of four onion cultivars Agrifound Rose, Bellary, Prema-178 and Nasik Red exposed to salt stress with different concentrations of NaCl (0, 50, 100, 150 and 200 mM). In all cultivars, morphological parameters and relative water content decreased with increasing NaCl concentrations, whereas antioxidant enzyme activities, proline accumulation and Na + / K + content increased. Bellary cultivar showed highest salt tolerance than the Agrifound Rose, Prema-178 and Nasik Red. Decrease in RWC was least in Bellary as compared to other cultivars. The results suggest that high NaCl concentrations have a negative effect on the physiological quality of onion seedlings, resulting in lower seedling growth rates and increased antioxidant enzyme activity and among four cultivars Bellary was found more tolerant to salt stress. Keywords: catalase, ascorbate peroxidase, glutathione reductase, morphological parameters, salt stress, proline. _____________________________________________________________________________________________ INTRODUCTION Salinity is a major problem in many parts of arid and semiarid regions of the world [1]. It also has an adverse effect on the growth and development of most salt sensitive plant species [2]. Nearly 20 % of world’s cultivated area and 50 % of the world’s irrigated lands are affected by salinity [3]. Salinity causes morphological, physiological and biochemical, molecular changes in the plants. Seed germination, seedling growth are adversely affected by high salt concentration, ultimately causing diminished economic yield, quality and productivity [4]. Successful seedling establishment depends on the frequency and ability of the seed species to germination. The decrease in germination race particularly under salt stress conditions may be due to the fact that seeds to prevent germination development and osmotically enforced dormancy under stress conditions. Plant growth is adversely affected by salinity from decreasing availability of water in the soil for plant consumption and toxicity of certain ions that contribute to salinity [5]. The mechanism of salt tolerance, cell turgor and depressed rates of root and shoot elongation, suggests that environmental salinity acts primarily on water uptake [6] Furthermore, high intracellular concentrations of both Na + and Cl - can inhibit the metabolism of dividing and expanding seedlings, retarding germination and even leading to seed death [7]. Salt stress can also lead to excess intracellular production of reactive oxygen species (ROS) such as the superoxide radical (O 2 •- ), the hydroxyl radical (OH - ), hydrogen peroxide (H 2 O 2 ) and singlet oxygen ( 1 O 2 ). To eliminate these