Effect Of Drought Stress On Photosynthetic Parameters And Sucrose-starch Synthesis Of Wheat Awns And Flag Leaves

Winter wheat,as the main food crop in northern China,is often subjected to drought stress during its critical growth period,which affects wheat production.The ear is an important photosynthetic organ of wheat,which has stronger drought resistance and photosynthetic persistence than flag leaves under drought.Awn is an important photosynthetic organ in the ear,and its photosynthetic contribution cannot be ignored.Therefore,studying the photosynthetic characteristics and sugar metabolism level of awn provides a theoretical basis for the breeding of drought-tolerant wheat varieties.In this study,drought-sensitive wheat Zhengyin 1 was selected.Through pot experiments,the photosynthetic characteristics of wheat awns and flag leaves,the changes of sucrose and starch content,the activities of related synthetic key enzymes and relative gene expression levels were measured under moderate drought stress.The contribution of awn to wheat photosynthesis and carbon assimilation synthesis.The main results are as follows:1.During the whole filling period,the net photosynthetic rate（P_N）of the flag leaves showed a downward trend.The P_N of awns rose and then fell,and reached its peak at 8 days after anthesis（8 DAA）.Under drought,flag leaves P_N decreased significantly（P<0.05）,while awn P_N had no significant difference（P<0.05）.At 12 and 24 DAA,flag leaves P_N decreased by 29.8%and 87.7%under drought-stressed treatment,while awns P_N only decreased by 5.7%and 11.4%,respectively.The transpiration rate（E）,stomatal conductance（g_s）and relative water content（RWC）in the flag leaves are consistent with P_N,but the peak appears at 4 DAA in the awns.Under drought,the E,g_s and RWC of the flag leaves decreased by 40.1%,76.2%and 13.9%at 24 DAA,respectively,while awns decreased by 20.9%,14.7%and 1.5%respectively.Chlorophyll content（Chl）showed the same trend in awns and flag leaves as P_N.At 20 and 24 DAA,the Chl of flag leaves decreased by 58%and 54.1%under drought,respectively,while the Chl of awns decreased by 11.3%and 12.3%,respectively.In addition,the intercellular CO₂ concentration（Ci）of the flag leaves showed an upward trend,and awns decreased at 0-4 DAA,and then slowly increased.The content of malondialdehyde（MDA）in both flag leaves and awns increased.It shows that under drought stress,awns have higher photosynthetic efficiency,better water retention ability and delayed senescence than flag leaves.In the later grain filling stage,awns can replace flag leaves as the main source of carbon assimilation.2.The relative expression levels of genes related to key enzymes of sucrose and starch synthesis showed a trend of increasing and then decreasing during the filling stage,and peaked at 8 DAA,which was consistent with the corresponding trend of enzyme activity.Under drought stress,the relative expression levels of related genes in flag leaves almost all decreased significantly（P<0.05）,but there was no significant difference in awn.At 16,20,and 24 DAA,the SS activity of flag leaves decreased by 20.1%,28.9%,and 30.1%under drought-stressed treatment,respectively,while the activities of awns decreased by 7.5%,9.6%,and 8.3%,respectively.Under drought,the activities of SPS in flag leaves decreased by 25.2%and 36.0%at 20 and 24 DAA,respectively,and the SPS activity of awns decreased by 15.2%and 14.8%,respectively.Under drought-stressed treatment,the activity of AGPase of flag leaves decreased by 27.8%and 32.3%at 12,24 DAA respectively,while that of awns decreased by10.7%and 7.9%,respectively.Under drought,the SSS activity of flag leaves decreased by27.8%and 36.2%at 20 and 24 DAA,respectively,while that of awns decreased by 15.0%and7.0%,respectively.Under drought stress,the contents of sucrose and starch in awns decreased compared with the control,but in flag leaves,there was no significant difference（P<0.05）.During filling,the contents of sucrose and starch in the flag leaves showed a trend of increasing and then decreasing,and reached the peak at 8 DAA.At 16,20,and 24 DAA,the flag leaf sucrose content decreased by 27.7%,34.0%,and 50.1%under drought-stressed treatment,while awns decreased by 14.8%,12.8%,and 18.2%,respectively.Under drought,the starch content in flag leaves decreased by 23.3%,32.2%and 46.4%at 16,20 and 24 DAA,respectively,and the starch contents in awns decreased by 8.1%,4.9%and 18%respectively.It shows that when the flag leaves cannot provide enough sucrose in the middle and late filling stage,awn still has the ability to continue to synthesize sucrose and starch and participate in grain filling.In short,under drought-stressed treatment,awns have higher photosynthetic efficiency than flag leaves,better water retention ability and aging delay,and when flag leaves cannot provide enough sucrose in the middle and late stages of grain filling stage,there are still relatively high ability to synthesize sucrose and starch to increase the contribution to wheat grain yield.