腐胺提高黄瓜根际低氧耐性的生理机理

 【目的】明确腐胺（putrescine，Put）对黄瓜根际低氧耐性的作用及其机制。【方法】以黄瓜为材料，分别在抑制和不抑制酸还原过程的条件下，在水培体系中对植物进行Put和根际低氧胁迫处理。【结果】外源Put显著提高了硝酸还原酶的实际（NRact）和最大（NRmax）活性，且这种作用在低氧胁迫植株中表现尤为明显。Put缓解了低氧胁迫下黄瓜叶片的净光合速率（Pn）、气孔导度（Gs）、胞间CO2浓度（Ci）以及根系线粒体总呼吸（Vt）、细胞色素途径呼吸（Vcyt）和交替途径呼吸（Valt）速率的下调。然而，当硝酸还原过程被钨酸钠抑制后，Put不仅失去了对光合作用及线粒体呼吸的缓解作用，反而进一步加剧了这两个基础代谢过程活性的下降。【结论】Put参与提高黄瓜对低氧胁迫抗性的作用和硝酸还原过程有关。

Physiological Mechanism of Putrescine Enhancement of Root-Zone Hypoxia Tolerance in Cucumber Plants

【Objective】 The purpose of this study is to investigate the physiological mechanism involved in the enhancement effects of putrescine (Put) on hypoxic stress tolerance. 【Method】 Cucumber (Cucumis sativus L.) seedlings were grown hydroponically and subjected to Put and root-zone hypoxia treatment with or without inhibition the internal nitrate reduction reaction. 【Result】 The actual (NRact) and maximal (NRmax) nitrate reductase activities were greatly enhanced by Put application, particularly in roots exposed to hypoxia. The reduction of leaf net CO2 assimilation rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci) together with the root mitochondrial respiration rate of total (Vt), cytochrome pathway (Vcyt), and alternative pathway respiration (Valt) were all greatly alleviated by the exogenous Put application. However, when nitrate reduction was inhibited by tungstate in the nutrient solution, Put not only failed to alleviate the hypoxia injury of leaf photosynthesis and root mitochondrial respiration, but also exacerbated the decrease of the activities of the two basic metabolic processes. 【Conclusion】 These results indicate that nitrate reduction process is involved in the enhancement effects of Put on root-zone hypoxia tolerance in cucumber plants.