(A–D) Effect of low temperature on superoxide dismutase (A), catalase (B), ascorbate peroxidase (C), and glutathione reductase (D) activities of ‘Baekbongdadagi’ cucumber leaves expressed on a milligram protein basis. Leaf 1 is the oldest. Enzyme activities are expressed as percentages of the control values (enzyme units, milligrams of protein per hour). APX, ascorbate peroxidase; CAT, catalase; GR, glutathione reductase; SOD, superoxide dismutase.