摘要：

It is well known that the drought stress may induce active oxygen species (AOS) generation and cause injuries to plants at various degrees. Defense enzymes such as SOD, POD and CAT etc, which clean AOS, exist in plant cells. AOS such as O ·- 2,OH · ,H 2O 2 were cleansed effectively and the degrees of lipid peroxidation and cell membrane injury were decreased by the compatible functions of these enzymes. Liquorices(Glycyrrhiza uralensis) can survive in some extreme environmental conditions such as dehydration, high and low temperature, high salt or alkali concentrations in the arid or subarid areas. Liquorices are very important in hampering wind, fixing sand and improving soil construction, but it is known a little about the mechanism of its tolerance to drought stress. In this study, Liquorices seedlings were treated with the osmotic stress solution PEG 6000(-2.5MPa,-1.5MPa). The content of MDA, cell membrane electrolyte leakage and several defense enzymes activities were measured at the different times after treatments. The content of MDA increased generally under -2.5MPa PEG stress, but decreased in the early stages of stress then increased to that of origirating state approximately under -1.5MPa PEG stress. The levels of the cell membrane electrolyte leakage were decreased in the early stages and increased in the later stages, the changed rate was slower under -1.5MPa stress than that under -2.5MPa stress. Several defense enzymes activities varied under -2.5MPa or -1.5MPa PEG osmotic stress: POD activities increased in all days except the first day; SOD activities raised and CAT activities declined, at 1 or 2d after treatment,but SOD activities decreased and CAT activities increased; ASP activities changed, which given a peak at the first and third day respectively under -2.5MPa stress. All of the alterations were in less extent under -1.5MPa stress than under -2.5MPa correspondingly. This results suggested that the system of the defense enzymes might play a key role by balancing all of the responding enzymes under drought condition in plants.

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