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In order to determine the mechanism of cold tolerance in crops, changes in biochemical factors related with the biological reduction of molecular oxygen upon cold shock treatment were analyzed at an early stage of Brassica germination. As the cold shocked seedlings were recovered under the normal growth condition for 24 hours, the peroxidase activities in cold sensitive rape(B. napus) and cold tolerant $quot;Sandongchae$quot;(B. campestris) were considerably increased by 33% and 87% in root fraction and, 84%. and 206% in hypocotyl, respectively. The content of superoxide(O₂) in hypocotyl fraction was dramatically accumulated until 8 hours after recovery and then gradually decreased. The extent of superoxide accumulation was severer in B. napus than 13. campestris. At 24 hours after cold shock, O₂ content was decreased to the nearly control level in B. campestris but still remained by 38% in B. napus. Even though H₂O₂ content in hypocotyl fraction was decreased only 2% in B. napes during cold shock, while in B. campestris it was severely decreased about 15%. On the other hand, the cold shock at 3 days after Uniconazole treatment was more effective in increase of peroxidase activity than each separate treatment.
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