Abstract: Effect of heat treatment and pretreatment (prior to heat treatment) with dimethylthiourea (DMTU, a trap for H2O2) on cell membrane injury and metabolism of reactive oxygen species in cucumbers stored at 2 ℃was investigated. The content of malondialdehyde (MDA), the chilling injury index and electrolyte leakage in control cucumbers were increased during the cold storage; H2O2 content, the activities of superoxide dismutase (SOD) and catalase (CAT) exhibited an initial fast increase followed by a reduction; the activities of peroxidase (POD) and ascorbate peroxidase (APX) were decreased with storage time. Heat treatment alleviated the chilling injury development, enhanced the endogenous H2O2 content during early storage, postponed the increase of MDA content and increased the activities of CAT, APX and SOD in cucumbers stored at low temperature. However, heat treatment had no significant effect on POD activity, suggesting that the enzyme did not play a key role in chilling tolerance in relation to antioxidant activity. On the contrary, DMTU treatment counteracted heat treatment-induced tolerance in cucumbers, exhibiting higher chilling injury index and MDA content, and decreased activities of CAT and APX. It is suggested that H2O2 mediated chilling resistance induced by heat treatment in cucumbers. 

Key words: cucumber, heat treatment, H2O2, antioxidant enzyme, chilling injury