The effect of cold acclimation on the freezing resistance and total soluble protein content in Populus tomentosa seedlings was studied for the first time in this paper. The results showed that in order to acquire higher freezing resistance, cold acclimation of Populus tomentosa seedlings might get through three periods, in which temperatures were -1℃、-2℃and -3℃ respectively. The freezing resistance of seedlings began to be induced by -1℃,but the third period of cold acclimation at -3℃ had most effect on the development of seedling freezing resistance. Suitable light could increase the freezing resistance and the content of total soluble protein of seedlings during cold acclimation, whereas 20 mg·L -1 of cycloheximide pretreatment of seedlings obviously decreased the freezing resistance and the content of total soluble protein. Further analysis found that the enhancement of total soluble protein content was closely related to the freezing resistance during cold acclimation.
