中文摘要：

通过测定自然降温过程中抗氧化系统、膜脂过氧化、NO释放量、NO合成酶（NOS）和硝酸还原酶（NR）活性的季节变化，研究植物内源NO在圆柏属植物祁连圆柏（Sabina przewalskii）和圆柏（Sabina chinensis）叶抗冻过程中的信号功能．结果表明：随温度降低，过氧化氢酶（CAT）、过氧化物酶（POD）、抗坏血酸氧化酶（APX）活性和谷胱甘肽（GSH）、脯氨酸（Pro）、类胡罗卜素（Car）含量增加并在冬季达最大值，NO释放率、NOS和NR活性以及丙二醛（MDA）含量也显著增加并在9月和2月出现两峰值；两树种叶中的抗氧化酶活性和抗氧化剂含量都与平均温度和MDA含量负相关，而且NO的产生总是发生在抗氧化酶活性和抗氧化剂含量增加之前，表明抗氧化系统在清除氧自由基抑制膜脂过氧化提高抗冻性方面具有重要作用，NO作为信号分子可能激活了抗氧化系统诱导植物抗冻性．在抗冻过程中，祁连圆柏叶的NO释放率、NOS和NR活性、抗氧化酶活性以及抗氧化剂含量都高于圆柏，表明祁连圆柏具有较强的适应性策略．

英文摘要：

The seasonal changes of anti-oxidative systems, lipid peroxidation, apparent NO-release, activities of NO synthase （NOS） and nitrate reductase （NR） in the leaves of Sabina przewalskii （SP） and Sabina chinensis （SC） were investigated to understand the role of endogenous NO, as a signal molecule in freezing tolerance of evergreen woody plants. The results showed that activities of CAT, POD and APX, contents of GSH, Pro and Car increase with temperature decrease, and the maxima appear in the winter. MDA content, the rate of NO release, NOS and NR activity increase markedly and reach two peaks in September and February, respectively. Meanwhile, with mean temperature decreasing from August to January, the correlations between the activities of POD, CAT, APX and contents of GSH, Car and Pro and the mean temperature and MDA content in the both species become negative. Furthermore, NO generation is always found before increasing of anti-oxidative enzyme activity and antioxidant content, indicating that the anti-oxidative systems play an important role in potentiating freezing--resistance of the plant and limiting the production of free radicals to protect membrane integrity. NO as an early signal molecule is able to induce the freezing tolerance by activating the anti-oxidative system involved in both anti-oxidative enzyme and antioxidant. On the other hand, SP shows a prevailing strategy in signal function of NO and has higher anti--oxidative enzyme activity and antioxidant content than SC in order to develop the tolerance to freezing.