International Journal of Agriculture and Crop Sciences. Available online at www.ijagcs.com IJACS/2013/5-4/401-409 ISSN 2227-670X ©2013 IJACS Journal Evaluation of total soluble protein and antioxidant activities in two spring cultivars of canola (Brassica napus L.) in response to low temperature Zeinab Moieni-Korbekandi 1* , Ghasem Karimzadeh 1 , Mozafar Sharifi 2 1. Plant Breeding and Biotechnology Department, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran. 2. Department of Plant Biology, Faculty of Biological Science, Tarbiat Modares University, Tehran, Iran. * Corresponding author email: Moeini_0010@yahoo.com ABSTRACT: Canola (Brassica napus L.), as the third oil seed worldwide, is an important resource in providing raw oil in Iran. The expansion of spring annual production is limited by high temperature during the flowering. In Iran where high temperature in summer appears to be premature, canola is cultivated in autumn or winter. However, spring cultivars are perceived to be low resistant to low-temperatures particularly in the early stages. In efficient physiological processes, they are induced in cold-tolerance. The present work aims at assessing the physiological traits of two spring canola cultivars: cold-sensitive (Option 500, cv.1) and cold-resistant (Zarfam, cv. 2). They responded to cold treatment at a four-leaf stage in terms of the amount of total protein and SOD (superoxide dismutase), POX (peroxidase) and CAT (catalase) antioxidant enzymes by a treatment comprising shifts from 22 °C to 10 °C. Variance analyses showed significant differences between sampling times, cultivars and temperature treatments as a result of low temperature (LT) on SOD, CAT, and POX. As a result of LT on protein content, there were significant differences between all sources of variation except between-temperature treatments. In both cultivars, antioxidant activity was changed differently, increasing significantly under low-temperature, in comparison with the controls but in Zarfam cv. cultivar, it was more. In cold-resistant the highest increase in protein content and SOD activity under low-temperature was observed in the second day. It was in the fourth day of POD and CAT activity that the features of cold hardening in Zarfam cv. were found. It shows the importance of cellular antioxidant machinery for protection against low-temperature. Keywords: Brassica napus L., Canola, Protein content, Cold stress, Antioxidant enzymes. Abbreviation: SOD- Superoxide dismutase; POX- Peroxidase; CAT- Catalase; LT- Low Temperature; ROS-reactive oxygen species; ANOVA-Analysis of variance INTRODUCTION The genus Brassica includes a number of important crop species used for various purposes, such as producing oil seeds, vegetables, fodders and condiments (Gustafsson et al., 1983). Oil seeds, along with cereals, are the second global food resources. One of the most important oil seed crops is canola (B. napus L.), which is the third oil seed in the world among annual oil seeds by yields >14% (Weiss, 2000). In Iran, Brassica napus L. is an important resource in providing raw oil due to its cultivation capability in various regions, high percentage and desired quality of oil. Therefore, the most important prerequisite in developing this crop is adapting varieties in different conditions (Naseri, 1991). Low temperatures cause more crop losses worldwide and may be a significant factor influencing plant distribution (Burke et al., 1976). During the last decade, many efforts have been made to understand the biology of Brassica species (Janda et al., 2003; Karimzadeh et al., 2003; Wang-hao et al., 2007;