Responses of antioxidant enzymes and compounds in strawberry (Fragaria x ananassa 'Toyonaka') to cold stress

The aim of this study was to investigate the responses of the antioxidative system of strawberry (Fragaria x ananassa 'Toyonaka') to cold stress. Strawberry seedlings were exposed to four temperatures (25 degrees C or control, 10 degrees C, 4 degrees C, and 0 degrees C) and the compounds and enzyme activities were determined during six evaluation periods (0, 6, 12, 24, 48, and 72 h). Malondialdehyde (MDA) and H 2 0 2 concentrations fluctuated and increased overall at lower temperatures. The production rate of superoxide radical (O-2(-)) increased continuously with all treatments. Cold stress increased antioxidant enzyme activities such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDAR), when compared with the control. Ascorbate (AsA) content reduced, however dehydroascorbate (DHA) showed a significant increase, as did the ASA/DHA ratio. The results suggest that the ascorbate-glutathione cycle is regulated in response to low temperature, but this mechanism and consequently regulation ability peaks and declines with exposure to cold stress.