Effect Of Doubled CO₂ Concentration And Water Stress On Growth And Development And Carbohydrate Metabolism In Cucumber Seedlings

To reveal effects of doubled CO₂ concentration and water stresses at the levels of 0 g/kg,50 g/kg,75 g/kg,100 g/kg of PEG 6000 on adversity acclimation and physiological indexes such as invertase expression, non-structure carbohydrate metabolism, activities of protective enzyme and osmotic adjustment substance of cucumber seedlings (Cucumis sativus L. cv. Jinyou No.1) seedlings were studied under hydroponic culture. The results were showed as follows.Under the condition of water stress, the invertase expression in leaves of cucumber seedlings was closely related to both the strength and the duration of water stress.The soluble acid invertases and the soluble alkaline invertase expressed significantly incresed under water stress. Invertases in leaves were increased under 75 g/kg PEG 6000 treatment several days after stress. The invertases were increased under 0 g/kg and 50 g/kg PEG 6000 treatments and decreased under 100 g/kg PEG6000 treatment with the strength of water stress in different stress days. The increases of glucose, fructose and sucrose in leaves were corresponding to the trend of leave invertases expression. The increasing degrees of glucose, fructose were significantly increased with the strength and the duration of water stress. The increasing degrees of glucose, fructose were maximum and sucrose was lower than glucose, fructose under various levels of PEG treatments in the duration of stress. The increasing degrees of starch were increased with the strength of stress. Furthermore, in the same level of water stress, the increasement of the invertase activity and the contents of non-structure carbohydrate were higher under the doubled CO₂ concentration than at normal atmospheric CO₂ concentration.The results showed that the doubled CO₂ concentration signigicantly enhanced the root activity, photosynthesis rate, the content of photosynthesis pigments, soluble protein and Proline in leaves of cucumber seedlings under various levels of water stress. Futhermore, under high CO₂ condition, the amplitude reduction of the transpiration rate and stomatal conduction were obviously decresed; in addition, elevated CO₂ concentration considerably increased the activities of SOD, POD and CAT, the intercellular CO₂ concentration, the conductivity and the content MDA also showed less increase under the latter condition.The results indicate that doubled CO₂ concentration seems to hace ameliorating effect on drought induced oxidative damage and significantly effective on the 75 g/kg PEG 6000 treatment specially.In a word, the research was concerned on non-structure carbohydrate metabolism, morphological index and invertase expression. The result showed that doubled CO₂ concentration improved the drought resistance of cucumber seedlings, and the effects were significant under moderate (75 g/kg PEG 6000) water stress. One purpose of the study was to to provide theory bases and technological parameters for cucumber culture under CO₂-fertilized greenhouse or changed climatic conditions in the future.