The relationship between seasonal changes in anti-oxidative system and freezing tolerance in the leaves of evergreen woody plants of Sabina

Abstract

Although the relationships between reactive oxygen species (ROS) and membrane damage, between anti-oxidative enzyme activity and chilling tolerance, and between antioxidant concentration and chilling tolerance are well documented, the mechanisms responsible for survival of evergreen woody Sabina plants to survive temperatures below − 30 °C are not well understood. In this study, seasonal changes in the activities of the anti-oxidative enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX), as well as levels of ascorbic acid (ASA), glutathione (GSH), proline (Pro), carotenoids (Car) and lipid peroxidation were examined in the leaves of Sabina przewalskii Kom. and Sabina chinensis (Lin.) Ant. Leaves were sampled at monthly intervals from the summer of 2004 to spring of 2005. Anti-oxidative enzyme activities and antioxidant contents were affected by declining temperatures in the autumn (September to October) and winter (November to January) and increasing temperatures in the spring (February to April). Activities of POD, CAT and APX, as well as contents of ASA, GSH, Car and Pro increased with the decrease in temperature. The highest values were found in the winter. In contrast, the leaf content of thiobarbituric acid-reactive substances (TBARS) increased markedly in the autumn and remained relatively constant during the following winter. In the autumn, presumably in anticipation of acclimation during the winter, leaf freezing tolerance was closely correlated with the activities of anti-oxidative enzymes and contents of antioxidants, indicating that anti-oxidative systems in the leaves played an important role in limiting the production of free radicals to protect membrane integrity. Freezing tolerance in evergreen woody plants of Sabina is correlated with an increased capacity to scavenge or detoxify ROS by the anti-oxidative system. ROS accumulated as part of the cold acclimation response may induce anti-oxidative defence systems for the acquisition of freezing tolerance in the leaves. The results also suggested that a better capacity for anti-oxidative defences in S. przewalskii might account for its greater capacity for freezing tolerance than S. chinensis.