Effects of Chilling and Ethanol Treatments on the Antioxidant Systems of Cucumber Seedling Roots

Abstract

Previous experiments have shown that soaking 24-hr-old cucumber seedlings in ethanol leads to an increase in chilling tolerance. Seedlings were immersed in a 500-mM ethanol solution for 2 hr prior to chilling, rinsed, and placed in chilling immediately after treatment. All seedlings (except the control group) were treated for 2 hr after a 24-hr germination period at 25°C and a second group was held for 3 hr to allow the ethanol-induced chilling tolerance to dissipate. At this time, the seedlings were retreated with a second ethanol treatment identical to the first. The induction of chilling tolerance seen in both treatment groups was measured as an increase in root growth and decreases in lipid peroxidation and electrolyte leakage after exposure to chilling temperatures (2°C). Although ethanol treatment does clearly enhance chilling tolerance, the mechanisms by which it does so are unclear. Some hypotheses have suggested that ethanol acts as an anaesthetic, preventing a membrane phase change from a liquid to a gel-like state. Other evidence indicates that ethanol is a scavenger of the hydroxyl radical, working in concert with enzymatic-reducing systems and antioxidants to directly prevent damage caused by active oxygen species. Because enzymatic reducing systems and antioxidants have been shown to combat stress, the activities of three H2O2-scavenging enzymes (catalase, glutathione reductase, and ascorbate-specific peroxidase), along with the relative concentrations of reduced and oxidized forms of glutathione and ascorbate as affected by both chilling and ethanol treatments will be discussed in relation to chilling susceptibility.