Study On The Nitrogen Absorb,Transport And Molecular Mechanism Of Different Nitrogen Forms Of Citrange

Citrus is an important fruit in the world.It is often planted by grafting method.While Citrus.sinensis?L.?Osb×Poncirustrifoliate?L?Raf?citrange?is a main rootstock of citrus and used widely because of its strong tolerance to Citrus tristeza virus.Nitrate nitrogen?NO₃^-?and ammonium nitrogen?NH₄⁺?are two inorganic nitrogen forms absorbed and utilized by plants.Blended Nitrate nitrogen and ammonium nitrogen was proved to be better for plant growth and has higher nitrogen use efficiency than single Nitrogen forms.But it is not sure why and how nitrogen forms and their ratios influence the nitrogen absorption and transportation mechanism of citrange.This paper took citrange as the experiment materials,and planted them in improved Hoagland nutrient solution with different forms and ratios of nitrogen to study the seedling growth,n';itrogen absorption kinetics characteristics,nitrogen transport,metabolism and allocation of citrange.It aims to provide scientific basis for improving nitrogen use efficiency and scientific fertilization in citrus production.The main results showed as follows:1.From the citrange growth indicates either aboveground or underground,the blended nitrogen forms were better than single nitrogen form.All seedlings'growth was inhibited,even poisoned by total ammonium.The mixed nitrogen treatment on the content of chlorophyll a,chlorophyll b and total chlorophyll were better than single nitrogen,and total nitrate was better than total ammonium.The No3?NO₃^-:NH₄⁺=5:5?treatment was better than the other treatments on the seedling growth since chlorophyll content was continually increasing and it would be good for its accumulation.2.The results on the total nitrogen,the phosphorus content,nitrate and ammonium content and distribution showed that the nitrogen,phosphorus content were all increased by the adding of NH₄⁺,and NO5?NO₃^-:NH₄⁺=0:10?was the best in the content of nitrogen and phosphorus content;While NO3?NO₃^-:NH₄⁺=5:5?was higher on the nitrogen and phosphorus accumulation than others.Nitrate and ammonium content were all increased by the addition of NH₄⁺,and NO3?NO₃^-:NH₄⁺=5:5?were favorable to nitrate accumulation in roots,NO2?NO₃^-:NH₄⁺=7:3??NO4?NO₃^-:NH₄⁺=3:7?could reduced significantly overground nitrate content.Ammonium content of NO5?NO₃^-:NH₄⁺=0:10?was at most in underground and NO4?NO₃^-:NH₄⁺=3:7?in overground.3.The results on seedling roots activity showed that NO2?NO₃^-:NH₄⁺=7:3?was the optimal treatment and all ammonium treatment was least.Studied the characteristics and kinetics of NO₃^-uptake indicated that the parameter of Vm,Km and?value were all raised at first time and then reduced as the NH₄⁺percentage increasing;while NH₄⁺uptake study indicated that the parameter of Vm and Km were all raised at first time and then reduced,but?value changed in complex.All treatments showed that VmNO₃^->VmNH₄⁺and KmNO₃^->KmNH₄⁺,it indicated that citrange love mixed nitrogen and needed more nitrate than ammonium.4.The results on the nitrate transporter genes analysis showed that CitNRT2.4 was not tested in seedling leaves and roots of all 6 genes,while other 5 genes?CitNRT1.1?CitNRT1.2?Cit NRT2.5?Cit NRT1.5?CitNRT2.7?were exit in all treatments.CitNRT1.2 was the constitutive NRT;Cit NRT1.1,CitNRT2.5,CitNRT1.5 and CitNRT2.7 were inducible NRT,and were induced in roots and leaves by a certain percentage of NO₃^-.The results on the ammonium transporter genes analysis in all treatments showed that 3 AMT genes were expressed in seedling roots and leaves of all treatments.CitAMT1.2 was maybe the main AMT type in roots;CitAMT1.1 and CitAMT2 were expressed in leaves mainly,and were all regulated by NH₄⁺concentration.5.The results on the Nitrate Reductase?NR?activity showed that the activity of seedling leaves and roots were all raised since the culture continuing,and NR activity of leaves were higher than roots'.The overground of NO2?NO₃^-:NH₄⁺=7:3?and NO3?NO₃^-:NH₄⁺=5:5?were higher than others.Nia gens analysis further showed that Cit Nia1?CitNia2?CitNia OA were all tested in all treatments,and CitNia1 and CitNia2 were the main NR genes in roots and leaves respectively,and these on NO3?NO₃^-:NH₄⁺=5:5?were higher than others.The effect on the Glutamine Synthetase?GS?activity and Gln genes of seedlings of all treatments showed that the GS activity of leaves were less than roots',and NO2?NO₃^-:NH₄⁺=7:3?and NO3?NO₃^-:NH₄⁺=5:5?were higher than others in roots;3 GS genes?CitGln1.3?CitGln HZ,CitGln 2?were all detected in leaves and roots,CitGln HZ was the main type genes of roots and leaves,analyzing further by phylogenetic trees and tested that its function was similar to GS1 family.