The Effect Of Different Drought Stress On Assimilation Accumulation?Translocation And Grain Filling During Wheat Grain Filling Stage

In arid and semi-arid areas where rain-fed agricultural,water deficit is one of the key factors limiting wheat yield.The formation of wheat yield can be regarded as the result of the source-sink-transportation metabolism of the assimilation in the plant.The sucrose,starch of leaf(source)and fructan stored in stem before anthesis are the main assimilates of wheat grain filling,which have an important contribution to crop yield.Wheat after-anthesis photosynthesis assimilation products and before-anthesis fructans accumulated in the stem are converted into sucrose,which are transported by long-distance arrival to grains for filling.Although the yield can be greatly increased through genetic breeding,cultivation management and other measures,the low level of inferior grains fullness limits the further increase of yield.Moderate drought is reported to promote the transport of assimilates,produce a compensatory effect,thereby increasing crop yields,but the relationship between drought stress on the accumulation of assimilates transport and its effect on grain filling of superior and inferior grains is not clear.The object of this study is to revealthe metabolic process of wheat assimilation in drought stress from the source-sink-transportation perspective of crop yield formation,and studies the mechanism of the transport of assimilate to inferior grains.This experiment was conducted in pot under the outdoor rain-proof shed of the Institute of Water and Soil Conservation of the Chinese Academy of Sciences during October 2018 to June 2019.The winter wheat cultivar is Changhan58,and the 10 th day after wheat anthesis began drought treated.The experiment inldcued Three water treatments,well water(WW),moderate drought stress(MD)and severe drought stress(SD).The purpose of this study is to investiage the effect of different drought stress on assimilate transport,and its relationship with weak grain filling.The results will provide theoretical basis for water-saving production,high-yield cultivation and breeding in this region.The main conclusions are as follows:1.For the sources orgin,flag leaf could maintaine water status,stomatal conductance,stabilized electron transfer efficiency and high photosynthetic capacity under slignhtly drought stress during the wheat filling period.sucrose-starch synthesis enzyme activity was ehanced in the flag leaf,thereby enhancing the assimilation ability of the leaves.The soluble sugar content in leaves increased by 5.40%?11.29% compared with the normal water level.In the the stem,slightly drought stress during the wheat filling period enhanced the activity of furctan exohydrolase(FEH)in the stem,mobilized the transport of stem assimilate to the sink(grain),the stem(source)assimilation transport rate is increased,that is,the transport capacity of the transportation is enhanced.The stem dry matter decreased by 5.40%?15.06% compared with the normal water level.However,under severe drought stress,the content of sucrose-starch,related enzyme activity and dry matter content in stem of flag leaves were significantly reduced,among which,on the 35 th day of anthesis,the photosynthetic rate(Pn)of flag leaves decreased by 65.19% compared with the normal water level.2.For the sink organ,slightly drought stress during the wheat filling period increased the activity of sucrose-starch synthase in the sink(grain),accelerated the filling of sink(grain),and promoted the filling of the inferior grains.Therefore,the photosynthetic compounds synthesized by the source(leaf)continue to be transported to the sink(grain),and in the form of starch accumulated in the sink(grain),thereby improving the quality of the wheat grain and increasing the yield of wheat.The content of soluble sugar and starch in the weak grains increased by 7.47%?9.61% and 0.43%?9.54% compared with the normal water level,respectively.However,under severe drought stress,the content of sucrose-starch and related enzyme activities in grains were significantly reduced,among which,the content of starch in the inferior grains decreased by 14.03%?17.91% compared with the normal water level.In short,the slinghtly drought stress during the wheat grouting period enhanced the activity of the source(leaf)sucrose-starch synthase,so that the synthesis capacity of the source assimilated substances maintained a high level.Improved the mobilization and transportation capacity of the assimilating substance stalks in the stem(source),accelerated the transfer of the assimilating substances in the source(leaf)to the sink(grain),and increased the activity of amylase in the sink(grain),thus promoting the accumulation of assimilates in the sink.By promoting the grouting of inferior grains,the quality of the grain is increased,thus increasing the yield,showing a certain compensation effect.In addition,moderate drought stress,wheat leaf stomata were closed,transpiration rate was decreased,and the loss of water was reduced,thereby improving the efficiency of water utilization,with a certain water-saving benefits.However,severe drought stress seriously inhibited the synthesis ability of the source(leaf),resulting in poor transport of the accumulated assimilates in the stem(source),limiting grain filling,thereby reducing the yield of wheat.