EFFECTS OF THE LOW TEMPERATURE ON DEFENSE ENZYME ACTIVITIES OF DIFFERENT CHILLING-TOLERANT SOYBEAN CULTIVARS DURING THE GERMINATION

The chilling-tolerant soybean cultivars Kottman and Tiefeng 31 and the chilling-sensitive soybean Shennong 8 and Dongnong 46 were used as experimental materials.Their seeds were germinated under low temperature,10 ℃ and 6 ℃.The changes of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT) activities were investigated,compared with those under 20℃,during seed germination stage.The results showed that the soybean cultivars with different cold tolerance presented remarkably change trends in the defense enzyme activities as the temperature decrease.Under 6 ℃,the tolerant cultivars Kottman and Tiefeng 31 presented a relatively stable and higher SOD activity during the middle and late stage of germination,and POD activity increased rapidly as the germination develops and was notably higher than the sensitive ones in all the process.Under the same low temperature,CAT activity in the tolerant cultivars and the sensitive cultivars decreased dramatically during the early stage of germination(0~9 d),then the tolerant cultivars CAT activity increased slightly as the germination develops,but the sensitive cultivars,CAT activity decreased slowly during the stage of germination(9~15 d),then increased slowly.These results suggested that SOD,POD and CAT activities in the tolerant soybean cultivars response quickly to low temperature during seed germination period,which activities were higher or more stable compared with the sensitive cultivars.There was a significant difference in CAT activity between the tolerant and sensitive cultivars under 6 ℃.This implied that CAT may play a pivotal role in reactive oxygen species metabolism during soybean germination.