Abstract: 【Objective】 Study on the relationship between the grain hardness and the endosperm composition and microstructure will benefit further understanding of the formation mechanism of grain hardness. 【Method】One hundred and forty-nine RILs and 2 NILs populations were developed from the cross of Zhengmai 9045(hard)×Yangmai13(soft). Using the RILs and NILs lines, the relationships between the grain hardness and the vitreousness, thousand kernel weights, protein content, total starch content, amyloase content and glutenin subunit composition were analyzed. The soft and hard grain transverse sections were also observed under the electron microscope. 【Result】The result showed that the soft grain texture of all family lines carries wild type Pin genes (Pina-D1a/Pinb-D1a) while hard grain texture carries mutant Pin genes (Pina-D1b/Pinb-D1a). The coefficient of variation of soft family lines was higher than hard lines both in Zhengzhou and Nanjing sites. The environmental impact on soft grain texture was more than that on hard grain texture. In RIL population, the highly significant correlation between hardness value and vitreousness, and correlation coefficient was lower in Nanjing site than Zhengzhou site, while the thousand kernel weight, protein content, total starch content and amyloase content with hardness value were not significantly related. There was no obvious difference between the hardness values of lines having high molecular weight glutenin subunit 14+15 and 7+8, while the hardness values of low molecular weight glutenin subunit Glu-A3b lines was significantly greater than Glu-A3c. The result of electron microscope observation showed that there was no obvious difference in the aleurone cells in soft and hard NIL lines, while there was a clear difference in endosperm cells between NIL hard line and soft line. The matrix proteins were clearly separated from the surface of starch granules in the hard line, anyhow they adhered in soft line. In NIL population, the highly significant correlation between the hardness value and vitreousness was proved, while no significant correlation between hardness and other grain characters were found. These characters are the thousand kernel weight, protein content, total starch content and amyloase content. 【Conclusion】The hardness value was the index to reflect the adhesion degree of endosperm protein and starch granule. It did not affect the endosperm density and seed shape. The protein content, total starch content and amyloase content did not affect the hardness value in a certain range, while the glutein subunits have some influence on hardness.

Key words: wheat , hardness , protein content , starch content , glutenin subunit