High Temperature On Starch Formation Of Wheat With Different Heat Tolerance

Wheat is the main food of mankind,playing a pivotal role in ensuring the food security.Wheat contains more than 70% starch,which is one of the main carbohydrates sources of human.In most wheat grown area,the highest temperature usually occurred during wheat grain filling stage,heat stress hinders the normal accumulation of wheat endosperm starch,resulting in decreased wheat yield and quality.however,disagreed results were obtained in the amylase and amylopectin deposition under heat stress in different research group,and the alteration of starch granules were also show conflicted results under heat stress in different studies,furthermore,there are few reports on the effects of high temperature on starch granules of wheat grain with different heat tolerance.It is necessary to clarify the fact that how the heat stress affect the starch composition and granules particles of wheat grain.Therefore,we need to explore the changes of starch composition and grain size of wheat grains under high temperature.Preliminary explored the mechanism of wheat starch granules response on the high temperature,there are few reports on the effects of high temperature on starch granules of wheat grain with different heat tolerance which lay the foundation for the further research of heat tolerance mechanism and screening high quality heat resistant wheat varieties.seven spring wheat lines with different heat tolerance were screened by the sowing experiment with the change rate of thousand kernel weight(TKW)as the index.The experiment was carried out by field experiment and growth chamber experiment.The change of starch granule and the ratio of amylose to amylopectin were studied.The field experiment was carried out by random sampling design and late snowing was used to provide the corresponding heat stress environment and the growth chamber was used to provide the heat stress in indoor environment.We got the following conclusions:1 The late sowing approach was applied and resulted in temperature increase during grain filling stage.Correspondingly,four lines(132,95,CS,94)showed significant decrease in grain weights,with more than 14% in reduction of grain weight,thus were assigned as heat sensitive lines,whereas the other three lines(44,32,228)displayed slightly declined grain weight and less than 5% in reduction of grain weight,hence were regarded as heat resistant lines.In heat stress condition,the mature grains showed a shrinking grain,the grain shape showed reduced width but increased length.Correlation analysis showed that decrease of grain width was significantly related to the reduction of grain weight(P=0.028*),and could explain 65.3% grain weight variation in late sowing wheat.2 The starch granules of wheat grain response to heat stress by changing the particle size,and the grain size distribution of wheat starch with different heat tolerance was different.In normal conditions,heat-sensitive varieties(132,95,CS and 94),the type A and type B granules could classified clearly based on granules diameter in control conditions,few intermediate granules(8-14?m)were observed.In contrast,intermediate granules didn't show specific less in granules distribution pattern of heat resistant lines(44,32 and 228).Under heat stress conditions,the particle size of type A granules show a general decrease in most investigated wheat lines,and heat sensitive lines show more obvious decrease than that in heat resistant wheat lines.Notably,more intermediate granules(8-14?m)were observed in wheat of heat stress condition,showed a similar granule size distribution in heat resistant wheat lines,whereas no remarkable alteration occurred in heat resistant wheat.3 The change of starch particle size under heat stress was accompanied by the change of amylose / amylopectin of wheat starch.Surprisingly,the amylose / amylopectin of heat tolerant lines(44,32,228)were all decreased,while most heat sensitive wheat lines(94,132,95)showed a increase amylose proportion.The same time,the amylose contents of heat tolerant lines were all decreased,while most heat sensitive wheat lines showed a increase amylose proportion.