Freezing stress effects on antioxidant enzyme activities, ion leakage and lipid peroxidation of olive (Olea Europaea L. cvs. Fishomi and Roughani)

Changes in freezing injury percentage, malonaldehyde (MDA; as indicator of lipid peroxidation), antioxidant enzymes activity and proline content were monitored in the leaves of olive cvs. Fishomi and Roughani under different freezing temperatures (-5, -10, -15 and -20°C for 10 h). The results showed that freezing injury (determined by ion leakage analysis) and malonaldehyde (MDA) content of Fishomi cultivar were significantly lower than Roughani ones. The activities of peroxidase (POD), catalse (CAT), ascorbate peroxidase (APX) and polyphenol oxdase (PPO) enzymes of Fishomi were significantly higher than Roughani cultivars. However, superoxide dismutase (SOD) activity Roghani cultivar was higher than Fishomi cultivar. The proline accumulated in leaves of Fishomi was significantly higher than Roughani during freezing stress. The results demonstrated that freezing injury percent was positively correlated with ion leakage percent and MDA content in both cultivars. In contrast, SOD, APX, CAT and PPO activities and also proline content negatively correlated with freezing injury percent. It can be concluded that the lower freezing injury percentage, ion leakage, and MDA content followed by the higher antioxidant enzyme activates as well as proline content in Fishomi cultivar is a consequence of more effective protective mechanisms.