Different Hypoxia Tolerance And Underlying Physiological Mechanism Among Cucumber (Cucumis Sativus L.) Varities

Thirteen cucumber varieties were adopted to investigate responses and differences of their growth and photosynthesis parameters to root hypoxia stress. We also explored change of respiratory pathway of Baoyou 1 and Zhongnong 8 under root hypoxia stress and tried to discover the physiological basis of different hypoxia sensitivity. The results were as follows:Growth of all cucumber varieties were inhibited to various degrees under root hypoxia stress by waterlogging. After 7 days hypoxia treatment, biomass of Huifeng declined most by 33.4% and that of Zhongnong 8 by 27.7%, whereas that ofBaoyou 1 only by 10.6%. Total nitrogen content of shoot of Suifeng was influenced mostly by 21.8% and that of Zhongnong 8 by 13.7% and that ofBaoyou 1 by 9.0%, whereas that of Lubachun 4 the least. The reason of growth inhibition was maybe due to decline to leaf chlorophyll content, stomatal conductance, which resulted in transpiration and photosynthetic capacity decreased. We used a (the percent of treatment/control) [treatment and control represent hypoxia and normal matrix cultivation respectively] to estimate the inhibition degree of different varieties. We introduce a of biomass as major index and combine other assay parameters to evaluate varieties. Four varieties of Baoyoul, Yuexiu 2, Lubachun 4 and Zaofulu had resistance to hypoxia stress. However Suifeng, Jinchun 2, Xintaimici, Zhongnong 8 were sensitive to hypoxia stress.Two cultivars of different tolerance of Baoyou 1 and Zhongnong 8 were selected to research mechanism of different hypoxia tolerance. During 5 days treatment root respiratory activities of two cultivars declined compared to control, but not in significant level. And root respiratory activities of two cultivars began to restore at 7th day, while that of Baoyou 1 had much more activity than that of control. Thisindicated that cucumber would develop acclimation gradually with hypoxia treatment and root respiratory activity inhibition decreased. Root LDH and ADH activities of two cultivars were both induced and showed low-high-low tendency with treatment. There was no obvious difference between treatment and control in Baoyou 1 root LDH activity. However treatment of Zhongnong 8 was significantly higher than that of control and also higher than that of Baoyou 1. Root ADH activity of Zhongnong 8 increased to the highest 3 days after treatment, while that of Baoyou 1 increased to the highest 6 days after treatment which lasted much longer and much higher than that of Zhongnong 8. During treatment activity of ADH was much higher than that of LDH. This indicated that under hypoxia stress cucumber produce ATP by alcohol fermentation pathway. Root NR activities were induced in both cucumber varieties under hypoxia stress. Induced NR activities of Baoyou 1 were significantly higher than that of Zhongnong 8. But NR activities of leaves in both cultivars declined significantly compared to control.