Effects of PEG and Chilling Stress on Some Physiological Characters of Tobacco Seedlings

After submerging tobacco seeds(NC89) with different concentrations (0,20%) of PEG solution, seedlings of tetraphyllous phase were treated with temperature ( 5℃) for 1 - 5 days in order to probe into the effects of PEG on some physiological and biochemical characters related to chilling resistance in tobacco seedlings. The results showed that 20 % of PEG not only increased the survival rate of seedlings after chilling stress at 5℃ temperature, but also increased the content of soluble sugar by 95.7 % , and the content of proline by 161.8 % in tobacco seedling leaves. In comparison with the control, the content of chlorophyll and nucleic acid and respiratory rate in seedlings treated with PED all increased significantly under chilling stress. At the same time, activities of superoxide dismutase (SOD) , catalase( CAT) were kept at a high level in tobacco seedlings submerged with PEG than that of control seedlings . The level of malondialdehyde(MDA) in the seedlings and the relative permeability of membrane and the O2- . formation in tobacco seedlings decreased during the chilling stress. The changes of physiological index before and after the chilling stress showed that the index were closely related to the chilling resistance of seedlings. These results suggested that 20% PEG had an effect on stability of membranes and increased the content of protective substance for cold tolerance in tobacco seedlings under chilling stress.