Photosynthesis Mechanism And Proteomics Analysis Of Greenhouse Cucumber Under High Temperature And Elevated CO₂ Coupling

Cucumber?Cucumis sativus L.?is an important vegetable for protected cultivation.The light resource is rich and the photosynthetic efficiency is high in northern summer of China,so it plays an important role in improving the quality and yield of cucumber.However,protected cultivation will inevitably generate high temperature stress in summer.Even if the wind is released,it will not alleviate,even cause pests and diseases.At present,the increase of atmospheric CO₂ concentration?CO₂ enrichment?has become the main component of global climate change,so the effect of CO₂ enrichment on plant growth and the structure and function of terrestrial ecosystem has become a hot research topic at home and abroad.Nowadays,it is generally believed that CO₂ enrichment can promote photosynthesis and improve the optimum photosynthetic temperature of plants.However,there is still a lack of research on the regulation mechanism of photosynthesis under the condition of high temperature and elevated CO₂ coupling,especially in proteomics.In this study,the grafting cucumber in greenhouse was used as the test material.The"Jinyou 35"cucumber was selected as the scion and the"Yunnan black pumpkin"as the rootstock.The effects of high temperature and CO₂ on the daily and long-term changes of cucumber photosynthesis;the effects of high temperature and different CO₂ concentration on cucumber photosynthesis,antioxidant enzyme activity and starch metabolism;and the effect of high temperature and elevated CO₂ coupling of cucumber leaf proteome were studied to explore the physiological and molecular response mechanism of photosynthesis in greenhouse cucumber under high temperature and CO₂ enrichment.The main results are as follows:1.The response of cucumber photosynthesis daily and long-term change to the condition of high temperature and CO₂ enrichment.The photosynthesis of cucumber under high temperature treatment was obviously inhibited:the net photosynthetic rate,the activity of key photosynthesis enzymes,plant height,stem diameter,leaf area and single melon weight were significantly reduced.High temperature and CO₂ enrichment treatment could significantly alleviate the high temperature stress and significantly improve the net photosynthesis rate during the"noon break period".In the long-term treatment,it could accelerate the decomposition of starch,eliminate the"photosynthetic feedback inhibition"produced under normal temperature and CO₂ enrichment.Therefore,the photosynthesis in the whole treatment period can be improved under high temperature and CO₂ enrichment.2.The effect of high temperature and different CO₂ concentration coupling on cucumber growth and senescence.The treatment under high temperature and high concentration of CO₂?1200?1600?mol/L?could significantly promote the growth of single leaf,chlorophyll synthesis,the net photosynthetic rate,the activity of antioxidant enzyme,the content of starch and carbohydrate in the early growth stage?21 d?;and significantly reduce the carbohydrate content in the late growth stage?28 d?because of the starch accumulation,the decrease of starch decomposition capacity and the increase of malondialdehyde?MDA?content.The treatment under high temperature and medium concentration of CO₂?900?1200?mol/L?could significantly promote the growth of cucumber leaves,the net photosynthetic rate and the content of starch and carbohydrate and the photosynthesis during the whole growth period;the activity of antioxidant enzyme was significantly higher and MDA content was significantly lower than that of the control after 28 d,so the aging speed of the plant was slow,but the promotion effect in the early treatment?21 d?was less than that of the high concentration CO₂.The treatment under high temperature and low concentration of CO₂?500?900?mol/L?had no significant promotion on the growth of cucumber leaves,but it could increase the net photosynthetic rate significantly by increasing the chlorophyll content,and compared with the other treatments its MDA content was the lowest in the late stage?28 d?,which also played a role in delaying the senescence of plants.3.The effect of high temperature and elevated CO₂ coupling on the proteome of cucumber leaves.The number of different proteins and the proportion of up-regulation proteins under high temperature and CO₂ enrichment were both higher than that under high temperature stress,and many proteins up regulated by high temperature and CO₂ enrichment were all down regulated by high temperature stress.GO enrichment analysis suggested that differentially expressed proteins under high temperature and CO₂ enrichment only involved in response to biological processes,while differentially expressed proteins under high temperature stress related to biological processes,cell component and molecular function.Therefore,it is speculated that the influence of high temperature stress on the cell components and molecular functions of cucumber leaves can be alleviated,even eliminated,by regulating the differential protein expression under high temperature and CO₂enrichment,and thus photosynthesis of cucumber was promoted finally.