The results indicate that high protoplast quality corresponds to high stress tolerance. The damage of cell membrane is one of the important mechanisms of stress. The protective enzyme system(superoxide dismutase.peroxidase and catalase) plays an important role in stress tolerance. In the research of hormone it is suggested that ABA can induce chilling torlerance, and the mechanism may correlate with the special gene expression. The results indicate that high protoplast quality corresponds to high stress tolerance. The damage of cell membrane is one of the important mechanisms of stress. The protective enzyme system (superoxide dismutase. Peroxidase and catalase) plays an important role in stress tolerance. of hormone it is suggested that ABA can induce chilling torlerance, and the mechanism may correlate with the special gene expression.