Studies On Polyamine Metabolism And Its Physiological Regulation Role Under Hypoxia Stress In Cucumber Seedlings

Cucumber cultivar of Jinchun No.2 was used as experimental material, cultivated hydroponically with nutrition solution and treated with hypoxia stress by precisely controlling dissolved oxygen in nutrition solution through dissolved oxygen controller, followed by treatment of polyamine, polyamine synthesis inhibitor and PAO inhibitor added to the solution. Then root growth, polyamine metabolism, active oxygen and changes of some related enzymes activity and photosynthesis of the seedling were studied. And physiological regulation role of polyamine in its adaptation to hypoxia stress was explored. Main research results were as follows:1. The roots growth of seedling was significantly inhibited under hypoxia stress, in which the root dry and fresh weights were only 38% of those of the control. However, contents of PAs notably increased, which mean that PAs were involved in the adaptation metabolism. External PAs could positively promote the root growth and alleviate the harm of hypoxia stress mainly in the form of Spd, while Put must convert to the active form of Spd or Spm. As to ethylene, it couldn't reduce the harm but aggravate it under the stress, because ethylene could increase the acceleration of Put and inhibit the synthesis of Spd and Spm, which further illuminated that Put would take effect only after converting to the active form of Spd or Spm.2. Determination method of PAO activity was modified to improve its stability and repetition. It was proposed the perfect reactant and pH range for the free PAO enzyme. On this basis , determination method was put forward for the binding PAO on the cell wall, including its sensitivity, pH range, reactant dependency and sampling section. It found there was some correlation between changes of the free and binding PAO activity( r₂=0.8815). Exogenous Spd and PAO inhibitor could increase PAs contents in seedling roots and alleviate the injury of hypoxia stress. PAO activity was higher than that of control 3-4 days after hypoxia stress, among which the binding PAO activity was 8.54 to 13.17 times higher than that of free PAO with nearly the same tendency (r²=0.8569⁰.8992). The hypoxia stress and enhanced PAO activity would trigger the rapid accumulation of H₂O₂, which would do great harm to seedling roots, while Spd and PAO inhibitor could reduce the H₂O₂ content and alleviate itsharm to cucumber seedling roots.3. Under hypoxia stress, MDA content increased strikingly and active oxygen content and some protective enzymes activity showed the same ascending tendency followed by descending. After exogenous Spd treatment, contents of MDA and active oxygen decreased significantly, while activities of SOD and POD were in a high level and that of CAT in a low level. There's a certain correlation between variations of SOD and O₂- and the same between variations of H₂O₂ and POD.4. Activity of H+-ATPase and H⁺-PPase in vacuole membrane decreased with different levels under root-zone hypoxia stress, while that of H+-ATPase in cell membrane didn't decrease but a little increased, 4 times more than that of H+-ATPase and H+-PPase in vacuole membrane. Exogenous Put and Spd could notably improve activity of H⁺-ATPase in cell membrane and had little effects on H⁺-ATPase and H⁺-PPase in vacuole membrane, which showed that exogenous PAs could alleviate H+ accumulation through regulation the activity of H+-ATPase in the cell membrane. These results illustrated H⁺ were mainly transferred to the outside of cell membrane and secondly to the vacuole to reduce the stress harm in cucumber seedling roots.5. Pn in cucumber leaves carried a downward inclination and was obviously lower than that of control 10 days after hypoxia treatment, while Pn would improve greatly after exogenous Spd treatment. There's a significant correlation between Pn and Ci. Gs and Tr varied greatly and Gs was significantly correlated with Tr, but insignificantly correlated to Pn. Under hypoxia stress Φc and CE decreased greatly while Spd could improve Φc and CE value. It stated that the photosynthesis inhib...