Changes in oxidative damage and antioxidant enzyme activities of barley (Hordeum vulgare L.) cultivars exposed to rewarming upon freezing stress

Objective: The growth of plants during recovery period after freezing stress is more important for winter cereals to survive frost. However, little research has been done on physio-biochemical changes in response to recovery or rewarming conditions in cereals. In this study, the changes in oxidative stress intensities and antioxidant enzyme activities were thus examined under cold acclimation (CA), short-term freezing stress (F) and rewarming (R) conditions in barley cultivars differing in cold tolerance in order to assess the changes in Reactive Oxygen Species (ROS) scavenging system. Methods: Electrolyte leakage, Fv/Fm ratio (quantum efficiency of PSII), the contents of hydrogen peroxide (H2O2), malondialdehyde (MDA) and free proline as well as the activities of ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) were measured in leaf and root tissues of spring-(Zafer-160) and winter-(Tarm-92) type barley cultivars. Results: A corresponding increase in the free proline content and activities of APX and GR, the levels of Fv/Fm ratio, electrolyte leakage and the contents of MDA and H2O2 remained unchanged for the leaves of both cold-acclimated barley cultivars. Decreased CAT activity was compansated by increased APX activity following F treatment in the leaves of both cultivars. On the other hand, F treatment caused a significant decrease in activities of APX, GR and CAT in the root tissues of both cultivars. After the R period was complete, the APX and GR activities were determined at maximum level in leaf tissues of both cultivars. It may be verified as lesser accumulation of H2O2 in rewarmed Tarm-92 leaves than those in Zafer-160. Conclusion: Lower amount of H2O2 accumulation in Tarm-92 compared to Zafer-160 in F and R might indicate a higher tolerance to freezing stress due to strong induction of APX and GR enzyme activities.