Effect Of Nitrogen Metabolism On Starch Synthesis In Grain Of Wheat With Different Quality

There are two metabolism paths, nitrogen metabolism and carbon metabolism during the development of grains in wheat. Both of them are interactional. They have completed the substance accumulation and codetermined the quality of seed together. Illustrating the regulation and effect mechanism of nitrogen metabolism to starch quality of wheat which has important significance both in theory and practice to instructed the production of wheat with different quality. Strong-, middle and weak gluten wheat each type has two varieties are used in this experiment and the aim is to study the effect of nitrogen metabolism on starch formation in grains of wheat with different quality.1. Difference in nitrogen metabolismThe change current of protein content has the pattern of high- low- high. The protein content of strong-gluten varieties was higher than middle-gluten and higher than weak- gluten. Protein content has nearly correlation with nitrogen assimilation and the activities of NR and GS. The ability of nitrogen assimilation of strong-gluten wheat higher than middle- and weak- gluten because it is have higher NR activity in flag leaf and higher GS activity in grain, its can offer enough substrates to protein synthesis and better to the accumulation of protein.2. Difference of the synthesis and metabolism of sucrose in flag leaf and grainThe sucrose content in grains performed was declining gradually during grain filling of wheat with different quality, the activities of SS, SPS in flag leaf and SS in grain all performed in the pattern of a single-peak curve during grain filling. Comparing the SS activity of flag leaf in different types, the result indicate that the activity of weak-gluten higher than middle-gluten and higher than strong-gluten wheat. The peak value of SS activity of middle- and weak-gluten types was higher than strong-gluten. Time of peak appearance of SPS activity in weak-gluten was earlier than middle- and strong-gluten wheat. It may be an important reason for the starch content of weak-gluten higher than strong-gluten wheat.3. Difference of activities of enzymes involved in starch synthesis in grainThe activities of AGPP, UGPP, SSS, GBSS, SBE, and DBE performed in the pattern of a single-peak curve during grain filling. The peak value of activities of AGPP, UGPP, SSS and GBSS of weak- and middle-gluten are higher than strong-gluten wheat significantly. It is indicated that weak- and middle-gluten wheat have stronger ability of starch synthesis than strong-gluten wheat. It is an important reason for the starch content of weak-gluten higher than strong-gluten wheat. Activities of SBE and DBE have no significant difference of wheat with different quality. The correlation between enzymes and accumulation rate of starch synthesis is different on the basis of different varieties and starch components.4. Microstructure of inner endosperm cells in strong- and weak-gluten wheatDuring grain filling, the aleuronic layer of two cultivars became thick and dense; the number of starch grain in inner endosperm is increased. Starch grain numbers in inner endosperm cells of GC8901 is less than LM21 at the same days. Compare with the same variety at the same day, starch grain is small and dense at dorsum, but at abdomen, starch grain is big and exiguous. GC8901 has one or two layers aleuronic layer, but LM21 has only one. That may be the primary reason why protein content of GC8901 higher than LM21.5. Effect of nitrogen metabolism on starch synthesisBefore 15 days after anthesis, the ratio of SPS to NR in flag leaf and the ratio of AGPP to GS in grain were low and had not obvious difference in wheat with different quality, but at this time, the activities of NR and GS of strong-gluten cultivars are higher than weak-gluten cultivars, which can offer more photosynthesis carbon to synthesize amino acid and protein. From 15 to 30 days after anthesis, the ratios of SPS to NR of flag leaf and the ratio of AGPP to GS in grain raised rapidly, the peak value of SPS/NR of weak-gluten cultivars are higher than middle- and strong-gluten cultivars significantly. The ratios of AGPP to GS of weak- and middle-gluten cultivars were significantly higher than strong-gluten cultivars. but at this time, activities of NR and GS of weak-gluten are low, activities of AGPP and UGPP which correlated with starch accumulation rate significantly and highly significantly are all higher than strong-gluten cultivars, so photosynthesis carbon were better used to synthesize starch, It was indicated that the size of SPS/NR and AGPP/GS ratio had the decisive effect to the photosynthesis carbon participated in carbon and nitrogen metabolisms.