中华蚊母树在干旱-水淹交叉胁迫下形态和活性氧代谢的适应机制

为阐明中华蚊母树（Distylium chinense）在消落带干旱-水淹交叉胁迫下的形态和活性氧（ROS）代谢适应机制，通过控制实验模拟了三峡水库消落带的水文节律，研究了干旱-水淹交叉胁迫及恢复过程施加不同外源物质对中华蚊母树形态学和ROS清除的变化。结果表明：（1）前期干旱胁迫增强了中华蚊母树对后期水淹胁迫的适应，主要表现在叶片脱落、大量不定根的形成及茎基部膨大等形态学的变化；（2）干旱或水淹单一胁迫下，中华蚊母树·OH、O₂^·等ROS水平明显高于对照，表现出氧化应激反应，其超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、抗坏血酸过氧化物酶（APX）等抗氧化系统酶活性及脯氨酸（Pro）等抗氧化系统小分子含量也均显著高于对照，表现出一定的抗氧化防御作用机制，且在复合胁迫下，SOD、CAT、APX酶活性及Pro含量显著高于单一胁迫；（3）恢复阶段，相关性分析表明，中华蚊母树清除ROS （·OH、O₂^·）的酶促（SOD、CAT、APX）及非酶促（Pro）系统具有一定的协同性。同时，恢复阶段施加脱落酸（ABA），内源Pro显著高于正常水平；施加Pro，SOD、CAT等抗氧化酶活性显著高于对照；施加可溶性糖（Glu），APX活性显著升高。表明外源添加ABA、Pro、Glu，均对ROS的清除产生显著影响，同时，SOD活性显著高于CAT和APX活性，因此SOD可能是中华蚊母树清除冗余ROS的主要因子。因此，中华蚊母树形态学的变化、较高的脯氨酸积累和对ROS有效的清除防御，可能是其适应干旱-水淹交叉胁迫的主要机制，ABA、Pro、Glu等外源物质的添加对中华蚊母树的胁迫恢复过程具有显著的促进作用，前期干旱可提高中华蚊母树植株对后期水淹的耐受能力。

Adaptive mechanism of morphology and reactive oxygen species metabolism of Distylium chinense seedlings to alternate drought and submergence stresses

Distylium chinense, the genus Distylium of the Hamamelidacea, is an evergreen perennial shrub between 0.8 and 1.2 m in height, native to the riparian areas and wetlands and a dominant species in the riparian areas of the Three Gorges Reservoir (TGR) region of the Yangtze River and its branches. Our previous studies showed that D. chinense had a certain survival rate in the middle and upper part of the water level fluctuation zone (WLFZ) of the TGR to alternate drought and submergence stresses, but the adaptive mechanisms of its morphology and reactive oxygen species (ROS) metabolism is still unknown. To evaluate its adaptation mechanisms of D. chinense to alternate drought and submergence stresses, a simulation alternate drought and submergence experiment was conducted, and morphology and ROS metabolism of D. chinense seedlings and their recovery growth with different exogenous substances, i.e., abscisic acid(ABA), proline(Pro) and glucose (Glu), were analyzed, including adventitious roots, plant height, base stem diameter, leaf numbers, ROS content, enzymatic and non-enzymatic antioxidant parameters. The results were as follows. (1) The early drought stress stimulated the adaptation of D. chinense seedlings to the later flooding stress.The adaptation mainly refered as more morphological changes of stems and roots i.e., stem base hypertrophy, formation and development of adventitious roots. (2) Comparing to the control group, there were significant increases in the ·OH and the O₂^· in D. chinense seedlings under either drought or flooding stress, which showed oxidative stress responses occurred and their superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities and the proline (Pro) contents were also significantly higher than those of controls, which showed that the enzymatic and non-enzymatic antioxidants were induced as a defense mechanism. Under the alternate drought and submergence stresses, the activities of SOD, APX and CAT and Pro contents were higher than those under single drought or flooding stress. (3) Correlation analysis showed that to a certain extent there were coordinated effects between the enzymatic (SOD, CAT, APX) and non-enzymatic (Pro) systems in ROS-scavenging in D. chinense. Exogenous ABA significantly triggered an increase of endogenous Pro contents compared to the controls during the recovery growth and the activity of SOD, CAT and APX was significantly higher than those of the control group under exogenous Pro treatment. Of these, the activities of SOD were significantly higher than those of CAT and APX. The activities of APX increased significantly when soluble sugar (Glu) was added. The ABA, Pro and Glu all had significant influences on the removal of ROS and the ability of D. chinense to up-regulate the SOD activity might be an important attribute for the removal of redundant ROS linked to drought and flooding tolerance. Thus the higher Pro accumulation and effective defense to ROS could be the main physiological adaptation mechanisms for D. chinense under the alternate drought and submergence stresses. The combination of morphological changes and the up-regulating of enzymatic and non-enzymatic anti-oxidative system might be the main mechanisms of D. chinense adapting to alternate drought and flooding stresses. The ABA, Pro and Glu treatment significantly promoted the recovery growth of D. chinense.. The drought in the early stage could improve the tolerance to submergence in the later stage.