Effects Of Post-silking Heat And Drought Stress On Grain Development Of Waxy Maize

The pot trial was conducted at Agricultural College of Yangzhou university in 2017-2019.Two waxy maize hybrids,namely Suyunuo 5(SYN5)and Yunuo 7(YN7),were used as test materials.The temperature was controlled by artificial intelligent greenhouse,and soil moisture content was controlled by weighing method.The grain yield,grain filling and development,enzymatic activities related to starch development,and endogenous hormone content under post-silking normal temperature(CK,28/20 ?,75%),heat stress(HS,35/27?,75%),drought stress(DS,28/20?,55%),and heat and drought stresses(HDS,35/27?,55%)were studied.The main results were as follows:1.Grain yieldPost-silking HS and/or DS significantly reduced the grain number and weight,which reduced grain yield ultimately.The grain numbers was similar between HS and DS in SYN5,but it in YN7 was higher under DS.The decrease of grain weight and yield was severe decreased under HS than that under DS.Among the three stresses,the decrease of grain yield,weight and numbers were most severe when drought and heat occurred simultanously.2.Grain filling characteristicsPost-silking HS and/or DS reduced the grain weight and volume at the middle and late grain filling stages,and the influence was severe under HDS.HS and/or DS accelerated the decrease of grain water content and shortened the filling process.Post-silking HS and/or DS significantly reduced the pericarp weights in the grain at the filling stage,and the effect was pronounced at the late filling stage than that at the early filling stage.The embryo and endosperm weights were increased by stresses at the 5-20 days after pollination(DAP),but the growth rates of the embryo,endosperm and pericarp weight were significantly restricted by stresses at the 25-30 DAP,which resulted in the decrease of weight at the late filling stage.3.Grain endosperm cell developmentHS and/or DS increased the volume of endosperm cells at 5 DAP,and there no amyloplast in the cells.The cell wall was obviously formed,and spherical nuclei developed.At 10 DAP,the endosperm cells began to accumulate spherical amyloplasts and the amyloplasts in the cells presented as clusters in the cells.The amyloplasts under CK and HS were similar,but the amyloplasts under DS were smaller than those of CK and HS.The amyloplasts of SYN5 were smaller than those of YN7 under HDS.At 15 DAP,the volume of endosperm cells in all treatments increased significantly,and the number and volume of amyloplasts in cells increased.In comparison with CK,stresses accumulated more amyloplasts,and present quickly filling status at 15 DAP,but the numbers of amyloplasts were similar between HS and HDS.At 20 DAP,the amyloplasts almost filled the entire endosperm cells under stresses(similar among HS,DS and HDS),but the number of amyloplasts under CK was less than that under stresses.At 25 DAP,the amyloplasts of all treatments were full of the whole endosperm cells and arranged closely.There was no significant difference in the size of amyloplasts among all treatments.At the 30 DAP,the amyloplasts were smaller under HS,and there was no significant difference among the other treatments.4.Grain component metabolismPost-silking HS and/or DS reduced the contents of soluble sugar,starch and albumin,and increased the contents of total protein,globulin,prolamin and glutelin at the late growth stage.HS and/or DS significantly increased the grain GOGAT activity,and the activity was similar between HS and DS but was higher under HDS.The enzymatic activities of GOGAT,GS,SS,SPS,AGP,SBE,SDBE and SSS in the grains initially increased and decreased with grain filling proceeding.HS and/or DS after silking significantly reduced the enzymatic activities of AGP,SDBE,SBE,SSS,SPS,SS and GS in the grain,and they were mainly scheduled as CK>HS>DS>HDS at the later stage.HS and/or DS reduced the IAA content and increased the ABA content in the grain,and the effects of HDS were the greatest.The results of correlation analysis indicated that the yield was positively correlated with the enzymatic activities of GS,SS,SPS,AGP,SBE,SSS,SDBE,and IAA in the grain,and negatively correlated with the content of GOGAT and ABA.Lower activities of GS,SS,SPS,and SSS in the grain restricted the starch depostion at later stages and caused grain weight decrease,ultimately,induced grain yield loss.The negatively effects were aggravated when heat and drought occurred simultaneously at the grain filling stages.