The Physiological Mechanism Research Of Manganese, Copper And Zinc On Enhancing Chilling Tolerances Of Cucumber Seedlings

Under normal conditions, the contents of Mn, Cu and Zn in grafted cucumber leaves were higher than in own-root cucumber leaves, while the Fe was contrary. And the cold tolerance of grafted cucumber was evidently higher than own-root cucumber. In order to make clear the relationships between high contents of Mn, Cu, Zn and cold tolerance, the effects of increasing or decreasing the concentrations of Mn²⁺, Cu²⁺, Zn²⁺ in nutrient solution on the contents of Mn, Cu and Zn, the activities of SOD, POD and CAT, the MDA content, electrolytic leakages and the expressions of Cu/Zn-SOD and Mn-SOD under low temperature stress in grafted and own-root cucumber seedlings leaves were studied. The conclusions were below:1. In order to make clear the relationships between high contents of Mn, Zn, Cu and SOD activity in grafted cucumber, Mn²⁺, Cu²⁺ and Zn²⁺respective and different combinations were added into own-root cucumber leaves extractions in the third day during low temperature stress so that the contents of Mn²⁺, Cu²⁺ or Zn²⁺could be the same as in grafted cucumber leaves extractions. The results showed that adding Mn²⁺, Cu²⁺, Zn²⁺ respective and different combinations into own-root cucumber leaves extractions could enhance the SOD and its isoenzymes activities except the Fe-SOD activity. The sequence of increasing level was Mn²⁺+Zn²⁺, Mn²⁺+Cu²⁺, Mn²⁺, Cu²⁺, Mn²⁺+Cu²⁺+Zn²⁺, Cu²⁺+Zn²⁺and Zn²⁺.This research proved that the Mn, Cu and Zn in cucumber leave could affect the SOD activity and the higher SOD activity in grafted cucumber leave might be attributed to higher accumulation of Mn, Cu and Zn.2. The contents of Mn, Cu and Zn, the activities of SOD, Mn-SOD and Cu/Zn-SOD of own-root cucumber seedling leaves treated by high concentrations of Mn²⁺+Cu²⁺+Zn²⁺ as a whole in nutrient solution were higher than the control, while the Fe-SOD activity and electrolytic leakages were lower; When grafted cucumber seedlings were treated by low concentrations of Mn²⁺+Cu²⁺+Zn²⁺ as a whole in nutrient solution, the results were contrary. It showed that Mn²⁺+Zn²⁺+Cu²⁺ played a very important role on cold tolerance of cucumber seedlings. And it was proved that the more great absorbability of grafted cucumber seedlings after grafted by figleaf gourd was one of the important reasons that it could have stronger chilling tolerance than own-root cucumber seedlings. Both the contents of Mn, Cu and Zn and SOD activity of own-root cucumber seedling leaves could been increased by increasing the contents of Mn²⁺+Cu²⁺+Zn²⁺as a whole in nutrient solution, consequently its chilling tolerance could been enhanced.3. Increasing the concentrations of Mn²⁺,Cu²⁺or Zn²⁺respectively in nutrient solutions all could enhance the SOD, POD and CAT activities and reduce the MDA contents and electrolytic leakages in own-root cucumber seedling leaves, the sequence of their functions were Mn²⁺,Cu²⁺,Zn²⁺. When decreasing the concentrations of Mn²⁺, Cu²⁺or Zn²⁺respectively in nutrient solutions all could make the SOD, POD, CAT activities reduce and MDA content and electrolytic leakage increase in grafted cucumber seedling leaves, the sequence were Mn²⁺,Cu²⁺,Zn²⁺. So it could been approved that Mn²⁺was the most important in cucumber cold tolerance among Mn²⁺,Cu²⁺and Zn²⁺.4. The Mn content in cucumber seedling leaves continuously increased with the Mn²⁺concentration becoming higher and higher. But the relationships between cold tolerance and Mn²⁺concentration were not the direct proportion. The activities of SOD, POD and CAT were the highest, the MDA content and electrolytic leakages were the lowest when the Mn²⁺concentration was 20 times than the standard. But the differences of cold tolerance between 20×M and 3×M treatments were little.5. The different combinations of Mn²⁺and Cu²⁺or Zn²⁺ in nutrient solutions all could increase the contents of Mn, Cu, Zn and cold tolerance under low temperature stress. The biggest of SOD and its isoenzymes, POD, CAT activities and the lowest MDA content and electrolytic leakages were found in 3×MCZ treatment, but the differences between 3×MCZ and 3×MZ, 3×M were little. So the 3×MCZ, 3×MZ and 3×M treatments all could enhance the cucumber seedlings'cold tolerances.6. The Cu/Zn-SOD and Mn-SOD expressions and activities of increasing the concentrations of different combinations of Mn²⁺and Cu²⁺or Zn²⁺ in nutrient solution all were higher than CK, their mRNA expressions both reached the highest in the third day but Cu/Zn-SOD activity increased contiously and Mn-SOD activity reached the highest in the fourth day during low temperature stress, it showed that the Cu/Zn-SOD and Mn-SOD were expressed firstly, then their activities increased. Before three day during low temperature stress, the change rules of activities of Cu/Zn-SOD and Mn-SOD were the same as the mRNA expressions, it showed the transcriptional regulation was the main method to control the activities. In the late stage of low temperature stress, Cu/Zn-SOD and Mn-SOD expressions declined, but their activities still increased, this indicated the other factors were the main method in this stage. So it could make a conclusion that the SOD activity was codetermined by the SOD expressions and other factors.Through these experiments, we had made conclusions that increasing the concentrations of Mn²⁺, Cu²⁺or Zn²⁺ could increase the contents of Mn, Cu and Zn, enhance the SOD and its isoenzymes, POD, CAT activities and cold tolerance of cucumber leaves. These indicated that the relationships between Mn, Cu, Zn and SOD activity were tight and Mn, Cu, Zn played a important role in cucumber cold tolerance. Among all treatments, the effect of Mn²⁺+Cu²⁺+Zn²⁺, Mn²⁺+Zn²⁺and Mn²⁺were the evident. Among Mn²⁺, Cu²⁺and Zn²⁺, the function of Mn²⁺was the largest, the suitable concentration was 2-3 times than the standard. And the higher SOD activity in grafted cucumber leaves than own-root cucumber was attribute to the higher contents of Mn, Cu and Zn. At the same time, it was found that through incesasing the concentrations of Mn²⁺, Cu²⁺and Zn²⁺ in nutrient solutions could be the effective methods to alleviate the cold disaster.