Study On Development Of Wheat Superior And Inferior Grain And Its Physicochemical Properties Of Starch

There are great differences in spikelet differentiation,development order,and flowering time between different spike positions and grain positions in wheat.Early flowering,good endosperm filling grain is called superior grain,and late flowering,poor endosperm filling is called inferior grain.The poor development of inferior grain and the low grain weight are the problems that have been solved in wheat production for a long time and have not been solved so far,which not only restricts the increase of yield,but also affects quality improvement.Starch is the main storage material in wheat endosperm,and its physicochemical properties are closely related to wheat quality.For this reason,in this study,the wheat variety "Yangjing No.1" and"Ningmai 13”were used as test materials.Semi-thin sections and light microscopy were used to observe the differences in the development of superior and inferior grain of wheat.Transcriptome sequencing technique was used to analyze the differentially expressed genes in superior and inferior grain of wheat at 15 days after anthesis.Morphology of amyloplast in superior and inferior grain of wheat was observed by using polarized light microscopy and scanning electron microscopy.Rapid viscosity analysis,thermodynamic analysis and X-ray diffraction techniques were used to compare the differences in physicochemical properties of superior and inferior grain.The main results are as follows:(1)There are significant differences in the development of pericarp of superior and inferior grain.The rate of exocytosis of superior grain exocarp was faster than that of inferior grain.In the supeiror grain,the accumulation of starch in mesocarp was more than that of inferior grain.The degradation time of intracellular starch was earlier than inferior grain,and the extinction time of superior grain in early grains was earlier than inferior grain,the stratum corneum of endocarp in superior grain between the transverse cells and the integument was significantly thicker than inferior grain.(2)There were significant differences in the development of amyloplasts and protein bodies in the endosperm of superior and inferior grain.The accumulation and number of protein body and amyloplasts in superior grain were significantly more than those of inferior grain.The emergence of amyloplasts in superior grain was earlier than that of inferior grain,the time of emergence of superior grain protein body was earlier than that of inferior grain,the superior grains were at 7 days after anthesis,and the inferior grains were at 10 days after anthesis.The number of protein body of superior grain reached its maximum at 20 days after anthesis,while the number of inferior grain reached the maximum at 25 days after anthesis.(3)The results of transcriptome sequencing showed that there were 2285 differentially expressed genes among superior and inferior grain,including 1200 up-regulated genes and 1085 down-regulated genes.There were 13,9,and 16 GO items involved in pericarp development,starch synthesis,and protein synthesis,respectively,and the related differentially expressed genes were 8,6,and 3 respectively.(4)There were differences in the accumulation of materials and the morphology and distribution of starch grains in superior and inferior grain.Compared with the inferior grains,the 1000-grain weight,the total starch content,the apparent amylose content,the total protein content,the gliadin and the glutenin content of the superior grain were higher.The small starch granules of superior grain and the large starch granules and the small starch granules of the inferior grain are standard "X" polarized crosses,but the large starch granules of the superior grain are disordered in the polarized cross and there are many micropores on the surface..Superior grain starch had a higher percentage of B-type starch granules but a lower proportion of A-starch granules.(5)There were differences in crystal structure,gelatinization characteristics and hydrolysis rate of superior and inferior grain.Superior grain starch had lower initial temperature,peak temperature,enthalpy value,breakdown value,and gelatinization temperature,but its setback value and solubility were higher.The relative crystallinity,single helix,and amorphous structure ratio of superior grain were lower,but the proportion of double helix structure was higher.The hydrolysis rate of superior grain was higher than that of inferior grain.The above research results not only could deepen the research on the development mechanism of superior and inferior grain,but also provide a theoretical basis for tapping wheat yield potential,improving wheat quality and using wheat starch.