Glutenin macropolymer is an important characteristic that affect significantly processing quality of wheat flour. It is determined by glutenin subunit composition and influenced by field environment during grain development. Application of nitrogen fertilizer is one of the most important measure to increase grain yield and protein content in winter wheat production. However, misuse of nitrogen fertilizer will not only affect grain yield, but also cause the decline of quality. To evaluate effects of nitrogen rates on GMP contents and GMP particles distribution in grains, a fertilizer experiment was designed with four treatments: without applying N fertilizer (N0), nitrogen rates of 160 kg/hm²(N1), 240 kg/hm²(N2), and 320 kg/hm²(N3), ratios of base fertilizer to topdressing of 1 ∶ 1, using two wheat cultivars differing in spike type. The plot area was 3 m×4 m = 12 m². At the three-leaf stages, the seedings were thinned to a density of 225 plants per m² for Taishan9818 (the large-spike cultivar), while for Shannong15 (the small-spike cultivar) that was 180 plants per m².
The results showed that application of nitrogen fertilizer increased markedly the GMP content in both cultivars, but, there were different patterns in response to nitrogen application between the two cultivars. Nitrogen application generally increased GMP content at nitrogen rate ranging from 0 to 240 kg/hm², and decreased when excessive nitrogen of 320 kg/hm² was applied in Shannong 15, while in Taishan9818, the content of GMP was increased within the nitrogen rates from 0 to 160 kg/hm², and decreased with the increasing nitrogen supply. This indicated that appropriate N fertilizer rate generally increased GMP content of wheat grain, while at the excessive nitrogen rate, the contents of GMP decreased. Taishan9818, the large-spike cultivar, was more sensitive to nitrogen in GMP content as compared with small-spike cultivar Shannong15. At maturity, the diameter of GMP particles changed in the range of 0.375-256 m. Volume and surface area distribution of GMP particles exhibited the typical two populations, while number distribution showed single peak curves. The D4,3 (weighted average volume) of Shannong15 was higher than Taishan9818, this contribution mainly came from the higher percentage of >100 μm GMP particle volume distribution in Shannong15. At the rage of 0-240 kg/hm², the percentage of <10 μm GMP particle volume distribution was decreased with the increasing nitrogen supply. It indicated that appropriate nitrogen fertilizer rate generally increased the percentage of lager particles volume distribution. The surface area percentage of 10-100μm and >100 μm GMP particle and the D_3,2 (weighted average surface area) were increased within the nitrogen rates from 0 to 240 kg/hm², and decreased when excessive nitrogen of 320 kg/hm²was applied, nitrogen application also increased the percentages of number of >10 m GMP particles. These indicated that appropriate nitrogen application promoted the formation of lager particles. The analysis of correlation showed that the content and proportions of GMP in total protein were positively correlated with the volume of >100 m GMP particles and sensitively with the D4,3. It suggested that the higher proportion of larger GMP granules was consistent with higher content of GMP in grains of wheat.