Effects Of Drought Stress At Booting Stage On Carbon Metabolism And Yield Formation Of Japonica Rice In Cold Region

As one of the main food crops in China,rice is an important determinant of food security.Heilongjiang Province,as one of the main rice producing areas,is responsible for ensuring food security in China.Drought has become the main reason for crop yield reduction in the world.Rice is most sensitive to water at booting stage.Drought stress at booting stage leads to degradation of a large number of rice branches and stems,decreases photosynthetic rate and dry matter production capacity,and has a significant impact on"sink"enrichment.It is of great significance to study the changes of rice from carbon metabolism to yield formation under drought stress at booting stage,so as to fully understand the disaster mechanism of rice under drought stress at booting stage.In this experiment,Songjing 6?SJ6?and dongnong425?DN425?were used as experimental materials to study the effects of different degrees of drought stress and recovery process on photosynthesis,accumulation of sucrose and starch in functional leaves and grains,transport and distribution of dry matter,grain filling dynamics,yield and its components at booting stage.The purpose of this study is to explore the accumulation of sucrose and starch and their molecular mechanisms in the process of drought stress and its recovery from the perspective of carbon metabolism;to clarify the impact of drought stress at booting stage on the yield formation of Japonica Rice in the cold region;to analyze the internal mechanism of the impact of photosynthetic material production,transport and accumulation on Yield Formation in the process of drought stress and its recovery at booting stage.This study provides a theoretical basis for understanding the response mechanism of carbon metabolism and yield formation to drought stress at booting stage and enriching the physiological basis of drought resistance of Japonica Rice in cold region.The main results demonstrated that:?1?Drought stress reduced the leaf area index of Japonica Rice in cold region,and the more severe the drought stress was,the greater the decrease of leaf area index was.Mild and moderate drought stress had little effect on SPAD value?Relative chlorophyll content?of Japonica Rice Leaves in cold region,but moderate drought stress showed a large decline rate of SPAD value after irrigation restoration,and severe drought stress significantly reduced SPAD value of leaves.Drought stress significantly reduced the net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO₂ concentration of Japonica Rice in cold region.After irrigation,the characters of light and moderate drought stress were restored to the control le vel in the filling stage,and the time of severe drought stress was longer.SPAD value and stomatal conductance were the main factors affecting net photosynthetic rate.Drought stress promoted the activity of ribulose-1,5-bisphosphosphate carboxylase/oxygenase?Ru Bis CO?in a short time,but after a period of drought,the activity of Ru Bis CO decreased;drought stress increased the maximum activity of fructose-1,6-diphosphate aldolase?FBA?.?2?Compared with the control,SJ6 concentrated more soluble sugar a nd sucrose in the stem sheath,less in the root system,and higher in DN425.Under drought stress,the activity of vacuolar invertase?VIN?in functional leaves increased significantly,and the higher the degree of drought stress was,the greater the increase was.Drought stress significantly reduced the activities of sucrose synthetase?Su Sase?and sucrose phosphate synthetase?SPS?in functional leaves,and affected the synthesis and degradation of sucrose.After irrigation,each treatment failed to return to the control level.Three enzymes,VIN,susase and SPS,work together to regulate the sucrose content in leaves.The decrease of net photosynthetic rate under severe drought stress is the main factor limiting the sucrose content.Drought stress significantly reduced the susase activity and SPS activity of strong and weak grains,and the susase activity of weak grains had the most significant effect on the sucrose content of grains.The VIN activity of DN425 strong grains was significantly higher th an SJ6.?3?The activity of ADP-glucose pyrophosphorylase?AGPase?and soluble starch synthetase?SSS?increased in weak grains under moderate and severe drought stress,but decreased significantly in DN425 strong grains under severe drought stress;the ac tivity of Granule-bound starch synthase?GBSS?was not sensitive to drought stress;the activity of Starch branching enzyme?SBE?increased in weak grains and strong grains under moderate and severe drought stress Under moderate and severe drought stress,the synthesis of strong amylopectin was affected,while the synthesis ability of weak amylopectin was enhanced;under mild drought stress,the content of total starch was not significantly affected,while under moderate and severe drought stress,the conte nt of total starch was significantly reduced.Drought stress significantly reduced NSC accumulation in roots,stems and sheaths and leaves.NSC accumulation in stem and sheath of SJ6 under severe drought stress was significantly higher than that under moderate drought stress,while the trend of DN425 was opposite.After resuming irrigation,NSC of both cultivars remained in vegetative organs under severe drought stress.Sucrose content and SSS activity were the main factors affecting starch content under drought stress,especially SSS activity of weak grains played a key role in starch synthesis in grain.?4?Drought stress significantly reduced the dry matter accumulation in all organs of Japonica Rice in cold region;after the restoration of irrigation,the dry matter accumulation in all vegetative organs of the two varieties under moderate drought stress and the stem and sheath of SJ6 under mild drought stress never recovered to the control level;a large amount of dry matter remained in the vegetative organs under severe drought stress.Different degree of drought stress significantly reduced the amount of dry matter transport after anthesis of Japonica Rice in cold region.Light and medium drought stress increased the rate of dry matter transport after anthesis of two varieties,increased the rate of dry matter transport and contribution of SJ6 leaves,and medium drought stress reduced the rate of DN425 leaves.?5?At booting stage,drought stress significantly reduced the grain filling rate of Japonica Ri ce in cold region,while slight drought stress significantly prolonged the active period of strong grain filling,but with the aggravation of drought stress,the active period of strong grain filling shortened;drought stress significantly prolonged the active period of weak grain filling.Drought stress significantly reduced the number of secondary branches and 1000 grain weight,and the number of effective panicles also decreased with the increase of drought stress;the grain filling rate of strong and weak potential mainly affected the yield indirectly by affecting 1000 grain weight,especially the grain filling rate of weak grain had a greater impact on 1000 grain weight.Drought stress significantly reduced the theoretical yield and actual yield of Japonica Rice in cold area.Under mild drought stress,the decline of theoretical yield and actual yield of DN425 was less than SJ6,and under severe drought stress,the actual yield of DN425 exceeded SJ6.?6?Combining with transcriptome sequencing,we found that the number of differentially expressed genes was the largest from the 6th to the 9th day of drought stress;combining with go and KEGG enrichment analysis,we found two time-specific invertase genes and four?-amylase genes involved in the metabolism of carbon and water compounds in functional leaves of Japonica Rice under drought stress;combining with WGCNA analysis,we found that the VIN activity was affected by b ZIP?Osb ZIP04?And WRKY?Os WRKY62?.