Abstract: The diurnal variations of electrolyte leakage, MDA concentration and cell defense enzyme in leaves of maize seedling were synchronously measured under the artificial conditions. The results showed that the variations of electrolyte leakage over a day-night presented respectively a dual-peaked curve with the maximum after 4 h of the light and after 4 h of the dark. MDA concentration in leaves presented a simple-peaked curve with the maximum in 4 h of the dark. With light continued, the activities of SOD, POD and CAT showed different levels of descend, but they came to the minimum of a day-night between four O’clock in the afternoon and eight O’clock in the evening. With the dark continued, the activities of defense enzyme all increased. But the rates of increasing were different, until eight O’clock in the next day, the activities of defense enzyme all reached the levels similar to the light before. Under the light and dark, the activities of all kinds of defense enzyme were significantly different. The diurnal variations of the activities of cell defense enzyme didn’t significantly relate to soluble protein content in leaves.

Key words: maize seedlings, cell defense enzyme, diurnal variation