The activities of catalase and ascorbate peroxidase in olive (Olea europaea L. cv. Gemlik) under low temperature stress

In this study, one-year-old shoots of the olive (Olea europaea L.) cv. Gemlik were tested at artificial low temperatures (4, −5°C, −10°C, and −20°C) every month for two years. For low temperature treatment, the degree of cell membrane injury in leaves and barks was determined by ion leakage method. In addition, with regard to antioxidative defense mechanism, activities of catalase (CAT, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.11) enzymes were determined. Leaf and bark tissues subjected to 4°C and −5°C injured to a limited extent in all months. However, more than 50% injury occurred by temperatures equal to or colder than −10°C treatments depending on the season. For −10°C and −20°C treatments, the lowest and the highest injury in leaf and bark tissues were detected during winter and summer seasons, respectively. We determined in this study that CAT and APX enzyme activities are generally higher during fall and winter compared with those in summer. On the other hand, CAT and APX enzyme activities started increasing during fall along with a decreasing freezing injury while the activities of these enzymes decreased to some extent during winter when freezing injury was the lowest. In addition, while CAT activity decreased with low temperature treatments, APX activity did not change until −5°C treatment but decreased with decreasing temperatures starting from −10°C depending on the month the tissue was obtained. In conclusion, olive plant shows considerable tolerance to low temperatures that are achieved after daily gradual decreases by increasing cell membrane stability through complicated mechanisms including antioxidative enzyme metabolisms. In addition, APX may be more effective in maintaining cold-hardiness of olive compared with CAT.