Primary Study On The Mechanism Of Physiochemical Properties Of Wheat Starch In Response To Nitrogen Application Stages In Sichuan

Wheat seeds are mainly composed of starch and protein,and starch accounts for 70% of the grain weight of wheat.Up to now,there is no systematic study on the effects of nitrogen application stage on starch synthesis,key enzyme activities of starch synthesis and gene expression of key enzymes in Sichuan wheat.In this study,the medium strong-gluten cultivars(Shumai 482 and Shumai 969)and two weak-gluten cultivars(Chuannong 16 and Mianmai 51),widely cultivated in Sichuan,were grown at Renshou and Chongzhou under the treatments with 3 nitrogen application stages: i.e.T1(only bottom fertilizer),T2(bottom fertilizer + fertilization at elongation stage)and T3(bottom fertilizer + fertilization at booting stage).The contents of total starch and its components,activities of key enzymes in starch synthesis,paste characters,starch structure and gene expression of key enzymes for starch synthesis under different treatments were compared.These results provide the possibility to understand the mechanism of the physical and chemical properties of wheat starch in response to nitrogen application stage,and provid useful data for wheat quality breeding in Sichuan.The main results are listed as follows:1.When comparing the T3 treatment with T1,the content of total starch and its components and the ratio of amylose to amylopectin in samples of Chongzhoul showed a downward trend;In the samples of Renshou,the amylopectin content was increased,and the remaining indicators showed a downward trend.It indicated that the content of total starch and its components are affected by both ecological environment and nitrogen application stage.In terms of starch pasting properties,the values of peak viscosity,trough viscosity,final viscosity,and breakdown were increased with the nitrogen application stage.Among them,the content of amylopectin was positively correlated with the peak viscosity,the breakdown value,the peak time,and the pasting temperature(P < 0.05).2.The activities of adenosine two phosphate glucose pyrophosphorylase(AGPase),starch synthase(SSS)and binding starch synthetase(GBSS)in Shumai 482 and Mianmai 51 were increased firstly and then decreased.At the early grain filling stage,there was little difference in the activity of the three enzymes between treatments.At the middle and late stages of grain filling,their activities were increased except for the GBSS of Mianmai 51.3.Electron microscopic observation showed that the numbers of A-and B-types of starch granules were respectively decreased and increased in three cultivars with the exception of shumai482,and the volume of B-Type starch granules became smaller with the shift of nitrogen application period.This reflects the effect of nitrogen application stage on the grain starch of wheat at the microscopic level.4.For the same cultivar,the expression patterns of AGP-L,WX-DI and SBE1 D were similar in the grain filling period,all of which were "single peak" curve.With the shift of nitrogen application period,the expression of WX-DI was enhanced in the early and middle stages,while those of other genes were reduced,when comparing the gene expression between treatments.This reflects the effect of nitrogen application stage on the starch at RNA level.