Response Of Wheat Grain Quality With Different Protein Content To Nitrogen Fertilizer Levels And Its Physiological Mechanism

This study was conducted to combine with field and pot experiments.In order to analyze the effects of cultivar,site and N rates on grain yield,protein and amino acid content in grains and processing quality of HPC and LPC wheats,and to determine the different responses to N rate between two groups of wheat cultivars.The field experiment were carried at Zhengzhou,Nanyang and Xinyang during two consecutive crop growing seasons of 2012-2013 and 2013-2014,used ten wheat cultivars with different protein content?4 LPC and 6 HPC?,under four N rates?0,120,225 and 330kg/hm²?.The pot experiment was carried out with three N rates?0,120 and 330kg/hm²?,used high-and low-protein content wheat cultivar?Wanmai16 and Luomai24?at Zhengzhou,to understand the nitrogen?N?rate on GS gene expression level,GS activity,protein accumulation,and the relationship of N metabolism and protein quality.The main results were as follows:1.The variation of gain yield and quality to environment and genotypeGrain yield,NUE,nutrition and processing quality were significantly influenced by cultivar,site and N rate,the significant interactions of them were also observed.For the three factors,grain yield,ANUE,starch content and quality were more likely influenced by site.The cultivar had the greatest effect on albumin content and farinograph properties.N rate imposed relatively high effect on the content of protein,globulin,gliadin and glutenin.Additionally,the amino acid compositions were also significantly influenced by cultiar,site,N rate and their interactions.EAAI and PDCAAS were significantly influenced by cultivar,N site,and the interactions of cultivar×site and site×N rate.For the three factors,site had larger effect on lysine,threonine,isoleucine and EAA.N rate had greater effect on leucine,phenylalanine and TAA.It indicated that breeding work and cultivation management should give full consideration of the environment affects for high yield and quality target.2.Response of grain yield and NUE in wheat culitvar with different protein content to N fertilizer levelsGrain yield of wheat had no significant difference between HPC and LPC,while LPC had significant increased ANUE compared with HPC at Zhengzhou and Nanyang.Added N fertilizer rate significantly increased grain yield,but declined NPFP and ANUE significantly.Considering both grain yield and NUE,the N rate of 120 kg/hm²obtained high grain yield for both HPC and LPC at the three sites.For the yield component,N fertilizer significant increased the spike number and kernels per spike,while decreased the TKW.It indicated N fertilizer mainly improved spike number and kernels per spike for high yield.Additionally,the accumulation and rate of grain filling between HPC and LPC were different.And their responses to N fertilizer also revealed variation.This was a main reason which resulted in different protein content in wheat grains.3.Response of amino acid in wheat grains with different protein content to N fertilizer levelsHPC got significant high essential amino acid compostions,EAA,TAA and EAAI,and it was significant at Nanyang.At Xinyang,it was only significant for lysine and threonine.Increasing N fertilizer rate significantly increased each amino acid composition,but declined EAAI and PDCAAS significantly.LPC had the greater NUE for amino acid content,compared with HPC.Considering both amino acid content and evaluation,N rate of 225 kg/hm²and 120 kg/hm²,respectively at Nanyang and Xinyang obtained the higher nutritional quality in wheat grains.4.Influence of N rate on protein,starch and processing qualityN fertilizer significantly increased protein,its fractions and GMP content.And it was mainly significant improved the gliadin and glutenin content,which increased the total protein content level.The responses of protein fractions in two groups to N fertilizer rates were different.The increased effects of N fertilizer rate on glutenin and GMP content were greater in HPC than that in LPC.It was a main reason for the formation of high protein content in HPC.Nitrogen fertilizer significantly declined the total starch content,amylase content and amylose/amylopectin.For farinograph characters,increased N rate significantly extended the formation and stable time,and also improved FQN.However,it significantly decreased peak viscosity,trough viscosity,final visocity and flour whitness.In the present study,N rate of 225 kg/hm²at Zhengzhou and Nanyang,120 kg/hm² at Xinyang obtained the high processing quality.Considering the grain yield,nutritional and processing qualities,and N efficiency,the N rate of 225 kg/hm² at Zhengzhou and Nanyang,120 kg/hm² at Xinyang were appropriate for wheat production.5.The relationship of N metabolism and protein accumulation,and their response to N fertilizer levleThe tendency of protein and GMP content in both wheat cultivars after anthesis showed the type of“V”with grian filling.And Wanmai16 had higher protein and GMP content.The N rate of 330 kg/hm² had greater increased effect on protein and GMP accumulation in Wanmai16,while lower N rate of 120 kg/hm² got the similar result in Luomai24.GS activity in flag leaf and grains of wheat declined during grain filling stage,which was slow at early stage,while rapid at late stage.Wanmai16?HPC?had higher GS activity both in flag leaf and grains.N fertilizer application increased the GS activity,and it was greater at early grain filling stage.GS genes expression levels showed similar tendency with GS activity after anthesis.Compared with N fertilizer applied,the control without N fertilizer induced the gene expression of GS1 and GS2both in flag leaf and grains.Between two N applied treatments,N330 obtained significant higher GS2 gene expression level at anthesis and early grain filling stage both in flag leaf and grains than that of N120.Similar,N330 significantly promoted GS1 expression level in grians during grain filling.Compared with the two cultivars,GS2 expression levels in flag leaf and grains of Wanmai16 were as 1.5-3.3 folds as that of Luomai24.This indicated that N deficiency induced GS gene expression,while high N level significantly increased GS gene expression level both in flag leaf and grain of wheat.Additionally,GS2 gene had greater function in protein synthesis.