| In this study,we selected twelve different type wheat cultivars to study starch granule size distribution,isolated starch pasting properties,accumulation characteristics of amylose and amylopectin,dynamic changes of the activities of key enzymes related to starch biosynthesis.At the same time,we selected different quality-type wheat cultivars and set three nitrogen fertilizer rates to study effects of nitrogen application rates on starch granule size distribution,composition of amylose and amylopectin,and starch pasting properties.The realtionship between wheat starch composition and pasting properties was also analyzed.The main results were as follows:1 The granule size distribution characteristics of wheat grain starch and its response to nitrogen application ratesMost of wheat endosperms had a unimodal or bimodal curve in starch granule number distribution,and a bimodal curve in starch guanule volume or surface area distribution.Few cultivars in our study showed a trimodal curve in starch granule number distribution and a trimodal curve in starch guanule volume or surface area distribution.The number and surface area ratioes of B-type starch granules were much higher than those of A-Type starch granule in wheat grains.But the volume ratioes of A-Type starch granules were commonly higher than those of B-type starch granules.There exised obvious difference in the starch granule distribution among different type wheat cultivars.The ratioes of B-type starch granules in waxy wheat grains were much higher than those in nonwaxy wheat grains.The ratioes of B-type starch granules in strong-gluten wheat grains were much higher than those in weak-gluten wheat grains.The nitrogen rates influenced the distribution of starch granules in different quality-type wheat grains significantly,and the influencing trend varied with genotypes.Increasing nitrogen fertility amount decreased the ratioes of B-type starch granules and augmented the average diameter and the middle diameter markedly in the endosperm of strong-gluten wheat.The peak diameters of B-type starch granules in the volume and surface area distribution enhanced markedly in the endosperm of strong-gluten wheat with the increasing of nitrogen rates.The B-type starch granule ratioes in the medium-gluten wheat enhanced with a reasonable nitrogen rate,at the same time,the average diameter and the middle diameter decreased.The B-type starch granule ratioes in the weak-gluten wheat enhanced significantly by increasing nitrogen rates,and the B-type starch granule ratioes of low nitrogen rate(LN) were the highest among those of three treatments.The average diameter and the middle diameter of LN in the weak-gluten wheat were lower than those of CK.2 The difference of starch accumulation and the enzymatic mechanism of starch biosynthesis in different type wheat cultivarsDuring wheat grain filling,the dynamic changes of starch content and accumulation were significantly different among waxy,nonwaxy and partial waxy wheat cultivars.The starch and amylopectin(AP) content began to increase quickly in nonwaxy and partial waxy wheat grains at 6 days after anthesis(DAA),and that was at 10 DAA in waxy wheat grains.The time of AP content stopped increasing quickly in waxy wheat grains was earlier than that in nonwaxy and partial waxy wheat grains.The starch contents in waxy and partial waxy wheat were commonly higher than those in nonwaxy wheat during grain filling after 10 DAA.The AP content in waxy wheat was much higher than those in nonwaxy and partial waxy wheat.The time of amylase(AM) accumulation increasing quickly in waxy wheat was much shorter than those in nonwaxy and partial waxy wheat.It resulted in the low AM content in waxy wheat.The AM content in waxy wheat was much lower than those in nonwaxy and partial waxy wheat.The dynamic changes of the ratio of AM to AP were significantly different during different type wheat grain filling stage.The ratio of AM to AP in waxy wheat was much lower than those of nonwaxy and partial waxy wheat.At initial grain filling stage (before 6 DAA),the activity of SS in waxy wheat was higher,the ability of degradation of sucrose was stronger,which appeared as the sucrose content was lower in waxy wheat.At the same time,the activities of UGPP and AGPP were higher,which suggested that the supplying ability of substrates to synthesize starch in waxy wheat was stronger.The activities of SSS,GBSS and SBE in waxy wheat were lower than those in nonwaxy and partial waxy wheat at initial grain filling stage,but the starch and AP contents in waxy wheat were higher than the two latters'.The dynamic changes of activity of AGPP were obvious difference in waxy,nonwaxy and partial waxy wheat during grain filling.The activity of AGPP continually increased in nonwaxy and partial waxy wheat grains after anthesis,which reached peak at about 20 DAA and then decreased.The activity of AGPP slightly decreased in waxy wheat grains before 6 DAA,increased quickly from 6-25 DAA,reached peak at about 25 DAA and then decreased.The activity of GBSS in nonwaxy and partial waxy wheat was much higher than that in waxy wheat during grain filling.The activities of UGPP,AGPP,SBE and DBE in waxy wheat were higher than those in nonwaxy and partial waxy wheat during the later grain filling stage,which was the important physiological reason for the higher and continual longer of AP content.3 Nitrogen rate affected the dynamic changes of starch content and accumulation during wheat grain filling markedlyIncreasing nitrogen fertility could decrease the AM content in wheat grain during grain filling.Increasing nitrogen fertility appropriately could heighten the starch content in wheat grain,but as the amount of nitrogen continued to increase,grain starch content might decrease.The changing trend of AP content was similar to that of starch content.Increasing nitrogen fertility could decrease the AM accumulation in wheat grain during grain filling.Increasing nitrogen fertility appropriately could heighten the AP accumulation in strong-gluten wheat cultivar YM47,but as the amount of nitrogen continued to increase,the AP accumulation decreased.Increasing nitrogen fertility appropriately could heighten the AP accumulation in medium-gluten wheat cultivar SN8355,but as the amount of nitrogen continued to increase,the increasing percent of AP accumulation decreased.Increasing nitrogen fertility could decrease the AP accumulation in weak-gluten wheat cultivar YM50 in the early stage of grain filling.During the later grain filling stage,the AP accumulation of LN increased quickly in weak-gluten wheat YM50,which was higher 2% than CK,but the AP accumulation of HN increased slightly and was lower than CK all the time.Increasing nitrogen fertility excessively could decrease markedly the starch accumulation in strong-gluten wheat cultivar YM47.Increasing nitrogen fertility appropriately, the starch accumulation of LN was mostly much higher than that of CK in medium-gluten wheatcultivar SN8355 during grain filling.As the amount of nitrogen continued to increase,he starch accumulation decreased markedly in the early stage of grain filling.The starch accumulations of LN and HN decreased markedly in weak-gluten wheat cultivar YM50 in the early stage of grain filling,the decreasing range was higher than 5% and it was higher than 10% sometimes.4 The pasting properties of isolated wheat starch and its response to nitrogen application rateThe peak viscosity (PV) and final viscosity (FV) of isolated starch from nonwaxy and partial waxy wheat were much higher than those of isolated starch from waxy wheat.The through viscosity (TV) of nonwaxy and partial waxy wheat was much lower than that of waxy wheat.It resulted in that the breakdown (BD) and setback (SB) of nonwaxy and partial waxy wheat were much higher than those of waxy wheat.The pasting temperature (PM) and peak time (PT) of waxy wheat were much higher than those of nonwaxy and partial waxy wheat. The PV and BD of strong-gluten wheat were much higher than those of medium-gluten and weak-gluten wheat,but its TV,FV,SB,PT and PM were much lower than those of the two latters.In strong-gluten wheat, increasing nitrogen fertility properly could increase the TV,FV,SB,PM and PT,but decrease PV and BD.As the amount of nitrogen increasing to 300kg/hm2,the PM and PT decreased,and thePV,TV,BD,FV and SB increased.In medium-gluten wheat,increasing nitrogen fertility properly could increased the PV,TV,FV and BD,but decreasing PM and PT.As the amount of nitrogen increasing to 300kg/hm2,the PV,TV,FV,BD, PM and PT increased.The RVA parameters of isolated starches from weak-gluten wheat declined after using more nitrogen fertility,and the decreasing range of LN was higher than that of HN.5 Relationships of wheat grain starch composition and starch pasting propertiesThe correlative analysis results indicated that there were close correlations between wheat starch composition,which included AM or AP content and granule size distribution,and starch pasting properties.The number, volume and surface area ratioes of B-type starch granules were significantly positively correlated with PV and BD,and were negatively correlated with TV,FV and SB significantly,and were negatively correlated with PT,but the former did not reach significant level.The AM, AP and starch contents of wheat grains were significantly negatively correlated with PV and BD,and were positively correlated with TV,FV,SB and PT.
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