The Influence Analysis Of Nitrogen And Phosphorus Starvation On Nitrogen Metabolism During Rice Vegetative Growth Stage

Rice is the most important crop in the world, especially in China. At present, the number of people is increasing day by day, while the cultivated lands are just the opposite in China. The contradictions among food safety, resource consumption and environment protection are increasingly sharp. The situation of grain yield have been embarrassed since 1998, we face a serious challenge on the rice production. As we all know nitrogen and phosphorus are the most important nutrient elements for crop production. Various chemical fertilizers especially nitrogen and phosphorus fertilizers were applied into the field in order to satisfy people's demand for food. However the chemical fertilizer utilization is decreasing. Overfertilization has not only greatly reduced the economic return of the fertilizers applied and placed a heavy economic burden on the farmers, but it has also resulted in widespread water eutrophication.We hope to provide theoretical foundations for nitrogen efficiency research, so we tested the concentrations of ammonium and nitrate in roots and the enzyme activities in plants which included NR, NiR, GS, Fd-GOGAT, NADH-GOGAT, NADH-GDH, NADPH-GDH, ICDH, AspAT, PEPc. We studied the influences of nitrogen metabolism with nitrogen and phosphorus starvation during rice vegetative growth stage from the physiological and biochemical view. The main results are as follows:1. The concentrations of ammonium and nitrate in roots significantly decreased in response to N-stress. At first, the expression level of genes NR1, NR2, NiR2, GS2, Fd-GOGAT, GDH2, GDH3 in shoots as well as NR1, NR2, GDH4 in roots were up-regulated, then decreased by N-starvation. In addition, the GS, Fd-GOGAT and AspAT activities in whole plant, NR, ICDH and PEPc activities in shoots, NADH-GOGAT activity in roots were decreased for N-deficiency. In contrast, the NADPH-GDH activity in shoots was increased. Both NR and GDH activities in roots were increased at first and then decreased after N treatment, while the NiR activity in shoots was just the opposite.2. The concentrations of ammonium and nitrate in roots were unaltered in response to P-stress. The activities of NiR, NADH-GDH, AspAT in plants as well as NR, GS, NADH-GOGAT, ICDH, PEPc in shoots exhibited no significant changes. But P-starvation resulted in a significantly increase of NADPH-GDH activity in shoots and ICDH activity in roots. The activities of NR, NADH-GOGAT, NADPH-GDH, PEPc in roots showed significant increases at the early stage of the P-starvation. After 7d of P-starvation, the GS, NADH-GOGAT and PEPc activities in roots were markedly reduced.3. The influences of nitrogen and phosphorus starvation on the concentrations of ammonium, nitrate in roots, and the activities of enzymes in plants were similar to N-stress, which were NR, NiR, GS, Fd-GOGAT, NADH-GOGAT, NADH-GDH, NADPH-GDH, ICDH, AspAT, PEPc.The results mentioned above indicated that, rice nitrogen metabolism activity was severely inhibited by longer N-deficiency treatment. But in the condition of adequate nitrogen, a short-time phosphorus stress may significantly stimulate nitrogen metabolism in rice roots. With nitrogen or phosphorus stress, the NADPH-GDH activity in shoots, and the NR, ICDH, PEPc activities in roots were all increased, indicating that they has important roles in response to nitrogen and phosphorus stress.