Mechanism Analysis Of Nitrogen Fertilizer And Irrigation During Seed Production Regulating Seed Vigor In Wheat

Seed vigor,a complex quantitative trait,is controlled by multiple genes and influenced by environmental factors.It is also one of the important indicators of seed quality.High seed vigor is associated with the potential for increasing growth and productivity in agricultural production.Fertilizer and irrigation play important roles in high vigor seed production.Researches on the effects of fertilizer and irrigation in the seed production on seed vigor are seldom,and the molecular mechanisms of fertilizer and irrigation regulating seed vigor are still unkown.In this study,we used wheat as material to investigate the effects of nitrogen fertilizer and irrigation on seed vigor.We study the mechnism of high seed vigor from aspects of physiology,transcriptome and proteome.We expected to find the common features of high vigor seeds.It can help us to know more about high vigor seed production in wheat.It is of great significance to keep rapid and uniform emergence of plants at field,high grain yeild and stable yeild.The main results were as follows:1.Nitrogen levels significantly affect high vigor seed production in wheatIn this study,we used wheat cultivar Tainong 18 as material.We set four nitrogen fertilizer levels,that is,N0(0 kg/ha),N168(168 kg/ha),N240(240 kg/ha,the usual nitrogen fertilizer level for winter wheat production in the North China Plain)and N300(300 kg/ha).Four nitrogen fertilizer levels significantly affected grian yield,germination,seedling establishment and seed vigor.Seeds of N168 and N240 had significantly higer seed vigor than seeds of N0 and N300.There were no obvious difference among four nigtrogen levels in germination energy(GE),germination percentage(GP)and germination index(GI).It was suitable for high vigor seed production in wheat under 168 kg/ha and 240 kg/ha nitrogen levels.N0(0 kg/ha)and N300(300 kg/ha)treatment caused low grain yield and seed vigor.Moreover,N300 might also cause lodging at late stage of grain filling.Therefore,we should keep suitable nitrogen level in seed production.2.The mechanism on rapid germination of wheat seeds produced under low nitrogen levelSeeds showed 0% radicle emergence at 8 h after imbibition(HAI).Seeds under N0 and N240 showed the highest and lowest radicle emergence from 12 to 24 HAI in two years,respectively.Seeds under N168 and N300 had slightly higher radicle emergence than N240 seeds,and all of seeds under four nitrogen levels showed at least 95% at 36 HAI.These observations indicated that N0 seeds germinated more rapidly than seeds under N168,N240 and N300.Further study showed that nitrogen fertilizer affects seed protein content,resulting in the changes of endosperm structure and eventually influencing water uptake and seed moisture content.Transcriptome analysis revealed that cell wall metabolism(GO: 0016998,cell wall macromolecule catabolic process,p = 1.99E-7;GO: 0004568,chitinase activity,p = 1.99E-7)accelerates radicle protrusion,thereby promoting seed germination.There were 30 cell wall metabolism related genes shwing down-regulation in 8 h imbibed N240 seeds.In these genes,the top four were chitinase that had about fourfold higher expression in faster germinated seeds.Protein metabolism(GO: 0006412,translation,p = 1.70E-5;GO: 0030529,ribonucleoprotein complex,p = 1.52E-4)in 8 h imbibed seeds of N240 was higher than that in 8 h imbibed seeds of N0,which might be due to higher protein content in N240 seeds.Moreover,faster germinated seeds had enhanced expression in glutathione metabolism,which might be related to scavenge ROS during seed germination.3.The mechanism on nitrogen fertilizer regulating seedling establishment and seed vigor in wheatThere were no significant among four nitrogen level in GI of wheat seeds.Therefore,vigor index(VI)was determined by seedling weight,which is influenced by seedling establishment.Seeds of N168 and N240 had significantly higher plant dry weight than seeds of N0 and N300.There were no obvious difference between seeds of N168 and N240 in plant dry weight.The changes of VI were consistent with the trends of plant dry weight.Transcriptome and proteome analysis revealed that pathways involved in nutrients mobilization(starch and sugar,nitrogen and linoleic acid metabolism)and glutathione metabolism showed enhanced expression during seedling establishment of high vigor seeds.Moreover,proteome analysis showed that the biggest difference of wheat seed protein was α-gliadin,and photosynthesis related protens were up-regulated in high vigor seeds.N240 seeds had significantly higher α-amylase activity than N0 seeds at 72 HAI,which was consistent with the gene expression level of α-amylase.Seedlings under N240 showed significantly higher plant dry weight than that under N0 from 3 to 8 DAI.The differences of plant dry weight between seedlings of N0 and N240 seeds increased gradually following seedling establishment from 3 to 8 DAI.N0 seeds had the highest germination speed,but seed vigor was the lowest one.This study confirmed that seeds with high germination speed might not mean high seed vigor.Comprehensive analysis of transcriptome at stage of seed germination and seedling establishment revealed that protein metabolism and nitrogen metabolism palyed important roles in regulating seed vigor.4.Drought stress after anthesis significantly affects high vigor seed production in wheatIn this study,we used wheat seed cultivar Shannong 20,Tainong 18 and Zimai 12 as materials.We set two soil moisture levels,that is,CK(Normal irrigation)and drought stress(Control rainfall and no irrigation)after anthesis.Drought stress after anthesis caused low grain yield and seed vigor,and the decreased degree was slightly different among wheat cultivars.Most wheat cultivars had lower GE,GP and GI under drought stress after anthesis than that under CK.There were no significant difference in GE,GP and GI of minority weat cultivars between under drought stress and CK.Therefore,we should keep suitable irrigation based on soil moisture at grain filling stage of seed production.5.Common features of high vigor seedsThe absolute content of protein and plant dry weight were extremely significant positive correlation based on analysis of seed vigor of multiple wheat cultivars and maize cultivars under several of treatments.When the difference of GI was low among treatments,plant weight determined VI.Therefore,the absolute content of protein could be used to evaluate seed vigor.The relative content of protein and 100-grain weight and plant dry weight were significant positive correlation in some experiments,but they were not suitable for all experiments.Moreover,correlation coefficient of these traits were lower than that of the absolute content of protein and plant dry weight.Validation experiment by using 30 wheat cultivars seeds stored about six months showed that the correlation coefficient of the absolute content of protein and plant dry weight was 0.897.Therefore,the absolute content of protein could be used to evaluate seed vigor of just harvest seeds or short time stored seeds,which accelerates seed vigor test.Moreover,the absolute content of protein could potentially be used to high vigor seeds sorting.