Effect Of HMW-GS On Formation Of Polymeric Protein And On Secondary And Micro Structures Of Gluten In Wheat

Gluten is the main component of dough and they are primary determinants of wheat end-use quality. The monomeric gliadin and polymeric glutenin comprise the gluten proteins. The high-molecular-weight subunits(HMW-GS) and low-molecular-weight subunits(LMW-GS) of glutenin combine to form the polymeric protein, thereby contributing to the strength and elastic properties of gluten. In this study, we clarified the effects of the HMW-GS on the polymerization of glutenin during grain development and on the secondary and micro structures of gluten by using six Xinong1718 near-isogenic lines(NILs) and two Xinong2208 near-isogenic lines. Totally, the polyacrylamide gel electrophoresis(PAGE), reverse phase-high performance liquid chromatography(RP-HPLC), size exclusion(SE)-HPLC, Fourier transform infrared spectroscopy, scanning electron microscopy were used. The results of the research are as follows:(1) The near-isogenic lines had variations of HMW-GS encoded by Glu-1, with identical LMW-GS and gliadin composition.(2) The polymerization of glutenin was monitored by the percentage of unextractable polymeric protein(UPP%). The near-isogenic lines with different HMW-GS composition exhibited changes in acccumulation of UPP%. At Glu-A1, the line with 1 subunit exhibited a steep increase in UPP% by several days earlier compared with the line with Null, and higher UPP% vaule was obtained in maturity seeds. At Glu-B1, the line with 17+18 subunits exhibited a steep increase in UPP% by 5 days earlier than those with allelic counterparts. Furthermore, the greater increase rate was maintained until maturity and thus the highest UPP% were obtained in line with 17+18. Line with 14+15 ranked second in terms of its higher UPP% value at maturity and had higher accumulation rate of polymeric protein, followed by 7+9, 7+8 and finally 6+8. At Glu-D1, the line with 5+10 started an earlier steep increase of UPP% several days earlier than 2+12; the line with 2+12 exhibited a faster increase rate of UPP% than line with only 12 at Glu-D1 locus. Therefor, the line with strength-associated alleles start to form larger polymers several days earlier than those without, and finally obtained higher UPP% in its’ mature seeds.(3) The near-isogenic lines with different HMW-GS composition exhibited changes in secondary structure of glutens. At Glu-A1 locus, the gluten of line with Null showed a lower proportion of β-sheet content and a higher ptoportion of α-helices and α-helix/β-sheet ratio. At Glu-B1 locus, the gluten of line with 17+18 had the highest β-sheet content, followed by 14+15, 7+9, 7+8 and 6+8. Contrastingly, the gluten of line with 6+8, had greatest α-helix content as well as α-helix to β-sheet ratio, followed by 7+8, 7+9, 14+15 and 17+18 subunits. At Glu-D1 locus, the gluten of line with 2+12 subunits and the line with 5+10 subunits showed no significant difference in β-sheet content, α-helix content, but significant difference in lower and higher α-helix/β-sheet ratio. The line with 2+12 had higher β-sheet content, lower α-helix/β-sheet ratio than line with only 2 at Glu-D1 locus.(4) The microstructure of the gluten in NILs exhibited significant differences. The freeze-dried gluten of NILs exhibited honeycomb-like structures, and the line with superior subunits showed more crosslinkage in its gluten. At Glu-A1, the gluten of line with 1 subunit showed larger pores and more crosslinkage than Null. At Glu-B1 locus, the lines with superior alleles(17+18 and 14+15) exhibited pores with appropriate size and heterogeneous distribution in the gulten structure compared with lines carrying other Glu-B1 alleles, whereas distinct tiny pores were found in the gluten cross linkage of line with 17+18. At Glu-D1 locus, the line with 5+10 showed distinct tiny pores in its crosslinkage and exhibited more cross linkage than 2+12; the gluten of line with 2+12 had a fibrous structure with more crosslinkage than line with 2 at Glu-D1.