Abstract:The generation of active oxygen and the activities of active oxygen scavenging enzymes as well as the effect of light on active oxygen metabolism were studied in soybean during germination. The O2 uptake, the rate of O2 production, and the level of H2O2 in imbibed seeds all increased at the beginning of germination, but all decreased after 4 days of imbibition. Gradual increases in activities of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) were observed at the early stage of germination, then the activities of SOD, POD, and APX tended to be in a certain level with little alteration. A new band of SOD isoenzyme presented respectively on the 2nd and 3rd day of seed imbibition. There was about a 50-fold increase in catalase (CAT) activity at the early stage of germination, and then turned stable. Among the three H2O2-scavenging enzymes (CAT, POD and APX), the capacity of CAT for scavenging H2O2 was much higher than those of POD and APX. So it seems that CAT is the most important H2O2 scavenging enzyme during germination. Although the O2 uptake of seeds germinating under light was lower than that in the dark, the rate of O2 production and the H2O2 level under light were higher than those in the dark. The ratio of O2- production to total O2 uptake was 1.1 - 2.7% in seeds germinated under light, while this ratio was 0.9 - 1.3% in the dark. The activities of SOD and APX under light were higher than those in the dark, but the activities of POD and CAT had no distinct difference under light and dark.