Effect of freezing desiccation on cold hardiness, ROS, membrane lipid levels and antioxidant status in spruce seedlings

Abstract

The symptoms of oxidative stress and antioxidative response were investigated on Norway spruce seedlings subjected to freezing desiccation conditions. Three-year-old seedlings were exposed to freezing desiccation at -3^oC and -10^oC for 45 days in two acclimation stages: autumn (October) and winter (January). The stress enhanced the production of reactive oxygen species (ROS): superoxide radical anion (O₂^.-), and hydrogen peroxide (H₂O₂). Concentrations of low molecular antioxidants: glutathione (GSH), ascorbic acid (AsA) and a-tocopherol declined at both low temperatures and acclimation stages. The activity of superoxide dismutase (SOD) increased with ROS production, while guaiacol peroxidase (POX) activity decreased. The freeze-induced desiccation of needles was significantly correlated with the cold hardiness (LT₅₀), the level of low-molecular antioxidants, and POX activity, but not with SOD activity. Under extreme freezing desiccation conditions, these reactions continued, leading to the degradation of membrane phospholipids and a strong decrease in cold hardiness. The results show that membranes are the primary site of injury induced by ROS, produced under the influence of low temperature combined with dehydration. The acclimation response of Norway spruce needles to the oxidative stress generated by long-term cold and/or freezing desiccation is discussed.