Photosynthetic Sugar And Its Transport Level Affecting Ammonium Absorption And Assimilation In Rice Roots

Rice cultivation occupies the important position in our country's agricultural production, and nitrogen nutrition play important role in promoting rice growth and development, increasing production and improving rice quality, etc. At the same time, with the increase of environmental pollution and enhancement of the environmental protection consciousness, reduce nitrogen fertilizer use and improve the utilization rate of nitrogen in the study of crop nitrogen nutrition is thus of key importance.In this study, using the hybrid rice strain HLY6 and its paternal cultivar 9311 as materials, In this study, using the hybrid rice strain HLY6 and its paternal cultivar 9311 as materials, we compared the photosynthetic sugar level and enzyme activities related to root nitrogen and carbon metabolism, and then through the sugar feeding in nutrient solution of 9311 to observe the influence of sugar for the metabolic difference between varieties, to investigate the reputational role of sugar to metabolism of roots. We tested a variety of metabolites content including sugar, protein and amino acids in root and leaf tissues as well as the changes of key enzyme activities of carbon and nitrogen metabolism in the root tissue. The results shown as follows:compared with the 9311, hybrid rice HLY6 had all kinds of comprehensive advantage in total soluble sugar (TTS), sucrose (Suc), fructose (Fru) and glucose (Glc).And related to metabolites in nitrogen absorption and assimilation, the soluble protein and a variety of carbon and nitrogen metabolism related amino acids in HLY6 were higher than in 9311, combining the advantages of activities of GS, NADH-GOGAT, NADP+-ICDH, PEPC and HXK in roots. The advantage of hybrid rice HLY6 compared with 9311 in physiological metabolism is indisputable. However, after adding sucrose in the nutrient solution of 9311, the physiological indicators in 9311, including several kinds of key enzyme activity of carbon and nitrogen metabolism, were rising sharply, many of them were close to or exceed the levels in HLY6. This suggests that the differences in the levels of sugar is perhaps plays important role in leading to hybrid rice and its parent have physiological differences in carbon and nitrogen metabolism.In order to confirm the important role of sugar metabolism for rice root, we treated HLY6 rice seedlings with DCMU, a inhibitor of photosynthetic. Results found after DCMU treatment, photosynthetic efficiency in HLY6 leaves dropped sharply, sugar levels and protein levels in the organization were significantly reduced, biomass had also been seriously affected. Carbon and nitrogen metabolism related enzymes in the root activity was also at very low levels. Ammonium nitrogen absorption and assimilation efficiency is decreased obviously. The above results showed photosynthetic sugar plays a important role of physiological metabolism in plant. When sugar added into the nutrient solution with inhibitor, can make up and restore, to a certain extent, the missing photosynthetic sugar for the roots of carbon and nitrogen metabolism, but recovery effect is quite limited, and more confined to the roots. The recovery of sucrose for the blade and the effects of biomass of plants are not obvious. This fully embodies the key role of photosynthetic sugar for the whole plant physiology.Spraying the sucrose solution on 9311 seedling leaves to mimic the increase of photosynthetic sugar contents, and the activity of carbon and nitrogen metabolism related enzyme in roots, as well as the metabolites content change were observed, to further reflect the regulation function of the photosynthetic sugar for the non-photosynthesis organization. According to the results, though the promotion of carbon and nitrogen metabolism levels in rice roots by spraying sucrose solution is weaker than adding sucrose into nutrient solution, the sugar level, protein level, amino acid content and the roots' enzyme activity level does exist obviously promoted. This results further evidence that the photosynthetic sugar can be regulation of physiological metabolism of the whole plant.The gene expression levels of SPS, a key enzyme of sucrose synthesis, as well as members of the family of sucrose transporters, SUT1,2,3,4,5, were investigated by RT-PCR. First, we found that there was a significant difference in the SPS gene expression in hybrid rice and their parents, while some of the sucrose transporters members had significant difference (SUT1,4), and others are not significantly different (SUT2,3,5). After inhibited by DCMU, SPS and SUT1 genes in HLY6 are a significant compensatory increased expression. When sucrose feeding to the nutrient solution of 9311, the SPS expression was significantly up regulated, while the sucrose is sprayed on blade, and its expression down regulated. SUT gene family members were sucrose-induced expression of the sucrose treatment except the SUT5. This fully reflects the important role of the sucrose transporters for sucrose transport. These results suggest that the sucrose synthesis and transport protein plays a very important role in the photosynthetic sugar regulation of plant physiology.In summary, the photosynthetic sugar has a very important role in regulating carbon and nitrogen metabolism of the non-photosynthetic tissues, this regulation is complex and sophisticated on the level of the whole plant, including sucrose synthesis and transport, many of the protease and transport carrier protein are having irreplaceable role in this process. In addition, the difference in sugar levels which lead to metabolic differences may be an important aspect of the presence of plant heterosis.