Abstract: The effects of magnesium deficiency on the growth and active oxygen scavenging system under different light intensities were studied in cucumber. The results showed that magnesium deficiency under high light intensity inhibited plant growth, however, magnesium deficiency did hardly affect plant growth under low light intensity. O-2 producing rate, H₂O₂ and MDA contents, and the activit ies of superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase in the leaves were considerably increased by magnesium deficiency under high light intensity, but were not significantly affected under low light intensity. There were no significant differences of catalase activity among all treatments.

Key words: Cucumber, Def iciency, Magnesium, Light intensity, Active oxygen, H₂O₂􀀁, scavenging enzymes