| In recent years,with the global warming and the frequent occurrence of extreme high temperature weather,the wheat production has been harmed to some extent,especially the high temperature in the filling period,which is easy to cause the premature senescence of wheat,and the yield has been greatly reduced,which has become one of the important factors limiting the wheat production.In order to explore the effect of nitrogen application period on the high temperature premature senescence of spring wheat after anthesis,this study took Ningchun 50 as the test material and adopted a split-zone test design.The main zone was five different nitrogen dressing period,set tillering stage and booting stage(N1,control),tillering stage and jointing stage(N2),tillering stage and heading stage(N3),jointing stage and booting stage(N4),jointing stage and heading stage(N5).The sub zone was temperature,set two temperature treatments of(25 ± 2)℃(control)and(35 ±2)℃(T).To study the differences of nitrogen nutrition on the growth status of spring wheat in the field,key enzymes related to starch metabolism and related regulatory genes.The main results were as follows:1.Under high temperature stress after anthesis,the chlorophyll content,SPAD value,fluorescence parameters Fv/Fm、Fv/F o、and PI of spring wheat all decreased in varying degrees.The total amount of chlorophyll、SPAD and PI of NT5 treatment increased by 5.2%、1.5%and 28.1%respectively compared with the control,which indicated that proper nitrogen topdressing could improve the function duration of leaves,delay the senescence of flag leaves of wheat,and facilitate photosynthesis of plants.2.The high temperature stress after anthesis makes the membrane lipid peroxidation of wheat flag leaves intensified and the protective enzyme activity decreases.The appropriate nitrogen chasing period can increase the protective enzyme activity and enhance the plant’s stress resistance.Compared with the control,the content of malondialdehyde and O2" in NT3 and NT5 were reduced by 3.5%,8.0%and 4.0%,9.4%.The activity of SOD increased by 12.8%only in NT5,and the POD and CAT enzyme activities increased respectively 10.3%,8.0%and 13.1%,0.1%,proline content increased by 2.1%,0.4%.3.Under high temperature stress,the content of soluble protein and nucleic acid in flag leaf decreased,the activity of protease and nuclease increased,and the content of soluble protein increased 26.0%and 28.6%in NT3 and NT5 treatments,The total amount of nucleic acid increased by 18.99%and 12.98%,DNA content increased by 25.99%and 24.35%,RNA content increased by 17.57%and 10.68%,endopeptidase and aminopeptidase activity decreased by 43.35%,45.2%and 17.7%,15.6%compared with the control,and nuclease activity also decreased compared with the control.4.Under high temperature stress after anthesis,the nitrogen content and Rubisco activity of NT5 and NT3 leaves increased by 1.8%、24.3%and 31.52%、32.61%respectively.Proper nitrogen topdressing can promote carbon and nitrogen metabolism of wheat and slow down the damage of high temperature to plants.5.After anthesis,high temperature stress reduced the activity of starch and key enzymes of starch synthesis in spring wheat,while appropriate nitrogen application period could improve the activity of starch synthetase in different degrees and promote the synthesis of wheat starch.NT3 and NT5 treatments increased amylose by 24.2%and 23.1%,amylopectin by 19.8%and 16.9%,total starch by 20.4%and 17.9%,respectively,compared with the control.Similarly,appropriate nitrogen fertilizer could significantly improve the activity of starch forming key enzymes(adpg-ppase,udpg-ppase,GBSS,SSS,SBE).6.In this study,RNA-Seq technology was used to sequence the transcriptome of spring wheat grain under post anthesis high temperature stress.It was found that there were 20 differentially expressed genes related to starch metabolism,7 of which were up-regulated genes,mainly involved in the biosynthesis of phenylpropionic acid,the metabolism of cyanamide acid and the metabolism of starch and sucrose,promoting the accumulation of starch in the grain;13 down regulated genes,mainly involved in pyruvate Metabolism,carbon assimilation of photosynthetic organic matter,biosynthesis of phenylpropionic acid,cyanamide metabolism,starch and sucrose metabolism,galactose metabolism and other pathways can inhibit the photosynthesis of wheat,reduce the transformation of photosynthetic products,and then affect the accumulation of starch in grains,reduce the weight of grains,and reduce the yield.7.High temperature stress after anthesis will reduce the number of grains per ear,1000 grain weight,seed setting rate and harvest index,and then reduce the yield of wheat.However,the number of grains per ear,1000 grain weight and yield of NT3 and NTS treatments are higher than those of the control.The number of grains per ear of the two treatments increased by 6.2%and 14.7%respectively,and the weight of 1000 grain increased by 1.30%and 6.10%respectively.In summary,proper nitrogen fertilizer backward movement,especially the application of nitrogen fertilizer at the heading stage,can effectively alleviate the harm of high temperature to wheat,improve the photosynthetic efficiency and antioxidant capacity of the plant promote plant protein and nucleic acid metabolism,accelerate the formation of grain starch,and then obtain more high production.Therefore,to change the traditional way of fertilization in production,in addition to applying nitrogen fertilizer in the critical period,adding a topdressing in the heading period can effectively resist the damage of high temperature on the plant in the filling period and avoid yield loss. |
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