The Brassica napus (canola) plant is a member of the Brassicaceae family. This crop is grown in various regions worldwide and has multiple uses, such as animal and human consumption, industrial products, and biofuel production. Canola is the second most-produced oil seed in the word after soybean. Plant employs effective methods to enhance plant growth and counter environmental stress factors. Salinity stress disrupts plant growth and development and causes oxidative stress in plants by producing free radicals. Plants have developed defense mechanisms to handle the negative effects of salt stress. These mechanisms include an enzyme antioxidant defense system to combat oxidative stress. This study examines how various NaCl and KCl salts impact the growth, enzyme function, and non-enzyme antioxidant defense system of the canola seedlings. The canola seeds were disinfected using a 1% bleach water solution and then washed. Similarly, the petri dishes and filter paper were soaked in bleach water before being washed with distilled water. To experiment, canola seeds were arranged with appropriate spacing on moist paper and placed in petri dishes. The experiment involved three replicates of each treatment including 80, 160, and 240 mM of NaCl and/ or KCl. Each petri dish was contained 40 seeds which put in an oven at 30 oC for germination. The number of seeds that germinated each day was counted to calculate the germination percentage and rare. The germinated seeds were collected after five days. The seed germination percentage and rate, fresh and dry weight of the shoot and root, the content of sodium, potassium, peroxide hydrogen H2O2, malondialdehyde (MDA) and DPPH radical scavenging activity was measured. In addition, the activity of the oxidative enzyme like peroxidase (POD), total superoxide dismutase (SOD), manganese superoxide dismutase (Mn- SOD) and copper/zinc superoxide dismutase (Cu/Zn- superoxide dismutase), polyphenol oxidase (POD), phenyl alanine ammonia-lyase (PAL) and lipase was evaluated. The current research indicated that the high treatment of KCl and NaCl reduced the germination percentage and rate. However, when canola seedlings exposed to NaCl indicated a more significant inhibitory influence may due to more toxic effect of sodium. Treating plant with KCl and NaCl at high concentrations was resulted in more reduction in the fresh and dry weight of shoots and roots. Likewise, the growth was inhibited stronger by sodium salt. In current study, the activity of lipase was substantially reduced in canola exposed to salinity (KCl and NaCl) at high concentration (240 mM) especially in plant exposed to NaCl salt. It has been observed the higher content of the MDA and H2O2 in plant exposed to NaCl compare to those of the plant exposed to the same concentrations of KCl. DPPH radical scavenging activity was significantly decreased at high concentration of NaCl (240 mM). When seedlings exposed to NaCl, the content of both potassium and sodium was increased. However, the toxicity was mostly due to sodium content that could attribute to imbalance of many important ions. The activity of total SOD was enhanced mostly due to an increase in the activity of the Mn-SOD with salinity stress. However, in this study the activity of POD was substantially reduced in canola exposed to salinity (KCl and NaCl) especially in plant exposed to NaCl salt. The activity of PAL enzyme went up with increase in the concentration of both types of salts. However, NaCl indicated a higher impact on the activity of PAL compared to KCl. Likewise, the activity of PPO was substantially enhanced with increase in the content of KCl and NaCl especially NaCl salt. Also, salt stress increased MDA and H2O2 content in canola plants exposed to high concentrations of both salts. These data strengthen the role of antioxidant defense system in salt stress conditions especially in plant exposed to NaCl.
