AB toxin produced by Alternaria brassicae could increase the membrane permeability in cell of Chinese cabbage. Results showed that there was a positive correlation between the susceptibility to A.brassicae and the change of permeability in cells of different varieties: the higher the conductivity was, the bigger the lesion was on leaf. Results also showed that the changes in activities of SOD and POD in cell were similar. Both of them decreased rapidly within 12 h after treatment and then incre...