Accumulation Of High Molecular Weight Glutenin Subunits In Wheat Grain As Regulated By Nitrogen Rate

Bread quality correlates closely with glutenin macropolymer (GMP) in wheat grains, which consists of high molecular weight glutenin subunits (HMW-GS) linked with low molecular weight glutenin subunits (LMW-GS) by disulphide bonds. Moreover, HMW-GS played key roles in determining the formation of GMP structure in wheat grain. The composition and amount of HMW-GS in different wheat varieties were different, and were relative to the industrial quality of wheat grains. The composition of HMW-GS present inheritance stabilization, but the content of HMW-GS was effected by environment and the cultivated measures. Recombinant inbred lines were used to investigate the contents of glutenin macropolymer (GMP) and HMW-GS, and to evaluate effects of T6VS·6AL chromosome translocation segment on contents of HMW-GS and GMP during grain filling in combination with effects of genetic background. Besides, the accumulation patterns of HMW-GS and GMP in different wheat varieties were also studied. The result should help clarify HMW-GS and GMP accumulation mechanism and provide regulatory approaches for super quality wheat. Total experiments were established as:Experiment 1:The aim of this experiment was to study analyze the dynamic changes in contents and accumulations of HMW-GS and GMP, and to evaluate effects ofT6VS·6AL chromosome translocation segment on contents of HMW-GS and GMP in wheat grains. Field experiment was conducted at the Experimental station of Nanjing Agricultural University in the growing season of 2008-2009. The wheat varieties for this experiment were two winter wheat (Triticum aestivum L.) varieties, i.e. Xumai 31 with high grain protein content and Ningmai 13 with low grain protein content, and four lines from an F8 RIL population, differing in grain protein content between two lines of each group (with and without the T6VS·6AL chromosome translocation segment).Experiment 2:The aim of this experiment was to study nitrogen rate effects on content of HMW-GS and GMP. Field experiment was conducted at the Experimental station of Nanjing Agricultural University for two years. Total three nitrogen rate treatment were established as 0,150 and 225 kg·hm-2.The main results were as follows:All HMW- glutenin subunits were detected at 13 days after anthesis (DAA) in grains of the four lines and the two wheat cultivars. However, the initial formation timing differed within subunits. The concentration and accumulation of the HMW-GS increased during the whole grain filling period, and the rapid accumulation occurred from 23DAA to maturity. Concentration and accumulation of HMW-GS of the higher grain protein content lines(wheat cultivar) were higher than those of the contrasting low protein content lines(wheat cultivar).Nitrogen showed no impact on the formation timing of HMW-GS in grain of both cultivars and lines. N fertilization showed a positive contribution to protein content resulting in an increase in both gliadins and glutenins. HMW-GS in grains accumulation rate was increased and the rapid accumulation period was prolonged with the increasing nitrogen rate, therefore, the contents of HMW-GS and GMP. Under the same nitrogen rate, content of each HMW-GS in grain with high grain protein content was higher than that in grain with low grain protein content. Therefore the accumulation of GMP and HMW-GS was speculated to cooperate with another protein in grain resulting in the isochronous change of the total grain protein. In conclusion, N showed a significantly regulatory effect on HMW-GS accumulation, especially their rates of accumulation during the grain filling period, which consequently led to differences in the final grain GMP content at maturity under different N fertilization rates. The fractionation pattern of individual subunits to total HMW-GS in response to N rate varied with subunit type. The responsibilities to N fertilization rates between four lines and two winter wheat varieties were different.T6VS·6AL chromosome translocation segment had no significant effect on content of GMP and HMW-GS. Grain gliadin content was found higher in the lines containing the T6VS·6AL chromosome translocation segment than those contrasting lines. The effect of T6VS·6AL CTE on the wheat quality might reflect in difference of quality and quantity of gliadin. Therefore the application of this germplasm resource was speculated to enhance the resistance to powdery mildew.GMP accumulation in wheat grain was found to depend greatly on HMWGS synthesis. In this study, significantly linear relationships were observed between GMP contents and individual encoded by different loci (Glu-A1,Glu-B1,Glu-D1) and total HMW-GS contents. The slope between HMW-GS content and GMP content at three nitrogen rate treatment was as follow: xumai31> 170>ningmai 13>49> 141> 194.The content of 5+10 subunit pair of xumai 31 was close to the content 2+12 subunit pair of ningmai 13. The content of 7+9 subunit pair of xumai 31 was close to the content 7+8 subunit pair of ningmai 13. However, the GMP content of xumai 31 was higher than ningmai 13. This implied that quality composition of glutenin subunits were in favor of consecutive macropolymer.