| Drought is a major yield limiting factor heavy affecting the crop grown and productivity,especially rice.C4 plants,such as maize,shows higher photosynthetic and water use efficiencies under drought stress than rice.Given virtue of C4 plant has variety different mechanisms to cope with the drought,Botanist hope to the key gene of C4 plant introduce to C3 plant rice via genetic engineering,to improve its photosynthetic efficiency,drought tolerance and yield.The key enzyme of v photosynthetic pathway,PEPCase(Phosphoenolpyruvate carboxylase)(PEPC,EC 4.1.1.31)not only increasing the C4 photosynthesis,but also the considerable part of plant resistant reaction,especially drought tolerance.Now,applying genetic engineering technology,it has got the miaze C4-PEPC transgenic rice(PC),showing higher net photosynthetic(Pn),carboxylation efficiency and grain yield than wild type rice,but also its has relatively stronger Pn and oxidative resistance in drought stress.However,How PC respond to drought stress of molecular mechanisms is still limited.Soluble sugar in plants is not only a key material,structure and energy,but also proved to play a important role in plant resistance to stress environment recently,full participation in the biological process of growth and reproduction,such as environment stress.Previous research has been found that under normal conditions,carbon and nitrogen metabolism enzyme activity of PC rice are higher than that of WT,and soluble sugar content was significantly higher than that of WT.We speculate that the soluble sugar may participate in regulation of rice drought resistance.In this paper,based on the high expression of maize PEPC gene in rice(PC)and wild type(WT)of rice as material,analysis of rice photosynthetic characters and production factors of artificial drought pot experiment and study of PEG-6000(Polyethylene glycol-6000,PEG-6000)simulation under drought stress,analyze the physical signs and ultra microstructure of rice leaf discs,analyze the soluble sugar regulation of genetically modified transgene rice drought resistance.The results are as follows:1.In the pot drought experiments,PC under drought stress compared with WT showed higher net photo synthetic rate,stomatal conductance and carboxylation efficiency,and PC under drought stress on thelater growing stage,compared with WT to maintain higher chlorophyll content.About the production,drought stress reduce the production both of PC and WT under drought stress.The yield of PC were significantly higher than that of WT whenever under drought stress or not..Under drought stress,each hole solid grain number,each hole total grain number per plant,grain,and the actual yield of PC is better than that of WT.And we measured rice stem weight,leaf weight and gross weight after harvest,PC were higher than that of WT.This shows that to compared with WT,PC in later stage of growth under drought stress that can maintain a relatively stable chlorophyll content,carboxylation efficiency in leaves to keep the net photosynthetic rate and stomatal conductance stability,thus reducing the bad effect on biological yield(dry matter weight)and rice yield(grain weight)under drought stress,then to improve the rice drought tolerance.2.To study the role of soluble sugar in the drought resistance of C4-PEPC transgenic rice,we use the rice leaf discs of PC rice and wild type(WT)as material,using 25%(w/v)PEG-6000 treated 3h to study the leaf water retention,MDA content,antioxidant enzyme activity,soluble sugar and various components in sugar,sugar metabolism related enzymes of SPS,SS,Invertase activity and metabolic enzyme gene related to carbon and SUT and the activity of PEPC enzyme and PEPC gene relative expression.in the control group and experimental group rice materials.Results showed that under the drought stress of PEG-6000,PC leaf discs has high water retention(P<0.05),lower MDA content(P<0.05),higher activity of antioxidant enzymes(P<0.05)compared with WT,showed better drought resistance.At the same time,the soluble sugar content in the PC leaf discs is higher than that of WT after drought treatment,and the glucose and fructose content increased significantly(P<0.05),and the results of sugar metabolism related enzyme activity,SPS and SS activity in PC leaf discs increased significantly,AIN activity is 13.3 folds than that of the WT(P<0.05),NIN activity is 37.3 folds than that of the WT(P<0.05),and PEPC enzyme activity increased significantly(P<0.05),while WT has no significant changes.Analysis of gene expression,PEG-6000 after processing,VIN1,CIN1,NIN1 and SUTs,PEPC in PC leaf discs is induced significantly increased(P<0.05).3.To study further analysis of PC drought resistance,we observed the ultrastructure of PC and WT leaf after the treatment of PEG-6000.Concluded from the results,after PEG treatment,of PC has no significant deformation,the chloroplast thylakoid lamella structure are tidy,and have more starch grains,but mesophyll cells complete structure of WT was loose,chloroplasts deformation occurred serious and collapse,and thylakoid lamella loosely,in addition that WT does not appear obvious starch granules.These results show that the PC can keep diachyma cells,chloroplasts,and thylakoid relatively complete form and structure,and in favor to maintain higher photosynthesis of leaf under drought stress to increase the drought tolerance.Altogether,PC leaves can maintain higher chlorophyll content,net photosynthetic rate and the complete cell ultrastructure under drought stress.And through the rapid mobilization of soluble sugar,strengthen the metabolism of sugar and sugar transport to enhance drought resistance,maintain the stability of yield under drought. |
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