Analyses Of Chlorophyll Degradation And Antioxidative Characteristics Of Flag Leaf And Ear Organs In Wheat Under Water Deficit

The contribution of ear organs to grain yield during the grain-filling stages could not be ignored,due to their better photosynthesis and drought-tolerance traits,especially under water deficit condition.Therefore,exploring the mechanism of high-efficiency photosynthesis and drought resistance in ear organs has theoretical guidance for wheat breeding.A winter wheat cultivar Pubing143 was used in this pot experiment,which was widely cultivated in the Northwestern China.In this study,we explored the effects of water deficit on chlorophyll degradation,chloroplast ultrastructure,chlorophyll fluorescence,antioxidant defense system and gene expression in the flag leaves and glumes during the grain-filling stages.It can provide theoretical evidence for further study to reveal the mechanism of ear organs resist drought.The main results as follows:1.Water deficit decreased the net photosynthetic rate(P_N)of flag leaves during the whole grain-filling stages,but the spike P_N had a peak at 6 DAA,and then decreased.Under water deficit,the flag leaf P_N decreased by 20%,23.1%at 12 and 18 DAA,the reduction rates of glume P_N(7.9%,20%)were less than flag leaf P_N.The Fv/Fm,NPQ and?PSII values decreased by 33.9%,20.4%,18.3%,while the glumes decreased by 16.0%,14.9%,11.9%,respectively.In addition,the chlorophyll contents(Chl)of flag leaves were higher than that of ear organs.These results suggested that compared with the flag leaves,the glumes can maintain higher photosynthesis,and the activities of glume PSII was more higher during the late grain-filling stages under water deficit.2.The activities of CHL,PPH in flag leaves firstly increased and decreased subsequently under water deficit,they reached the peak at 18 and 24 DAA,respectively.The glume CHL activities gradually increased,reaching the maximum at 24 DAA,then decreasing.The glume PPH activities increase during the whole grain-filling stages,but there was no significant difference between the treatments(P<0 05).The similar tends were observed in CHL,PPH expression.The expression of CHL in flag leaves were 1.24,1.21times higher than that in glumes,respectively,as for PPH were 1.24 and 1.18 times at 18 and24 DAA.But there was no significant difference of PPH between the flag leaves and glumes2.at 12 DAA(P<0.05).Under water deficit,the shape of chloroplasts began to smaller and the numbers of plastoglobuli increased in the flag leaves.The better developed chloroplasts with thylakoid membranes and starch grains were observed in the glume.3.Water deficit increased the ROS accumulation and the activities of SOD,CAT and POD.The flag leaves displayed deeper staining than the glumes at the middle and late grain-filling stages.The activities of SOD,POD and CAT in flag leaves increased at 0 and 18DAA,then decreased at 24 DAA.The similar tends were observed in POD,CAT and SOD expression.The glume CAT were significantly higher than that in the flag leaves at 24 and 30DAA(P<0.05),and the expressions were 1.55 and 1.53 times,respectively.As for the Cu/Zn-SOD in glumes,the expressions 1.21 and 1.74 times higher than that in flag leaves at18 and 30 DAA.Moreover,The expression of genes encoding Fe-SOD and POD in the glumes were also higher than that in the flag leaves at the middle and late grain-filling stages.In summary,ear organs showed higher photosynthetic characteristics and PSII activity,the chloroplast structure was complete,the chlorophyll degradation began late,and the antioxidant potential was strong at the late grain-filling stages.It helps the ear organs to maintain high light efficiency and delaying senescence at the late grain-filling stages.