Salinity is considered one of the most important environmental plant’s stress that is effective in all growth stages and as a limitation of agriculture crop production. This stress affects different physiological procedures that Oxidative damages to cellular components which are created by reactive oxygen species, are considered one the most important of them. In response, plants produce enzymatic antioxidants such as CAT, APX, and SOD to reduce the magnitude of these damages to the minimum. Azolla is a floating aquatic fern that grows in wetlands and has many usages such as bio-fertilizers in farms and animals’ food. Considering that Azolla also grows in sewers, it seems that it can withstand salinity. due to limited researches around the functions of genes and antioxidants enzymes of this plant, this research aims to analyze the effectiveness of salinity on the function and expression amount of CAT, APX, and SOD antioxidant enzymes gene of Azolla Filiciloides plant in four different salinity levels (0, 60, 90 and 120 Milimolar NaCl) and 2, 4 and 6 days of treatment. Therefore, first, the RNA components of all specimens have been extracted in the phenol-chloroform method and their cDNA has been synthesized. After designing specific primer pairs, the suitable connection temperature has been assigned by the PCR and the expression of the gene enzyme’s analysis has been conducted in a real-time PCR reaction. The function amount of the mentioned enzymes has been achieved with the extraction of plants sap sample and Spectrophotometry. Results show that at low levels of salinity the function and expression amount of SOD, CAT, and APX enzymes have increased significantly, but at 90 Milimolar, this increase only lasted for four days. At 120 Milimolar, the function and expression amount of all three enzymes gene showed no increase what so ever. Bearing in mind the results of this research, it seems that the activation of antioxidants enzymes defensive system has a major role in explaining the increase of salinity in Azolla’ s planting area. Key words: Salinity, Azolla , Antioxidant enzymes
