Abstract:

【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.

Key words: Cucumis sativus L., putrescine, photosynthesis, mitochondrial respiration, nitrate reduction, nitrate reductase