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1、PlantNitrogenAssimilationandUseEfficiencyWhatdidyoulearnfromthereview?SignalingNetworkinSensingPhosphateAvailabilityinPlants第四讲大量元素（氮）Section1GeneralIngeneral,0.3-5.0%ofdryweight.Varyingamongdifferentspecies,organs,growthstage.IncreasingwithApplicationofNFertilizer,especially
2、leaves!!Species:Legumes>Cereals,Maize>Wheat>RiceOrgans:Grains>Leaves>StemsGrowthStages:Tilling>Seedling(Rice),Vegetativeorgan>ReproductiveOrganFormsofnitrogeninplant:◆NH4+、NO3-，◆Lowmolecularorganiccompounds;◆Highmolecularorganiccompounds.VitalElement!!DNAandRNAChlorophyllEnzy
3、mesVitamin(B1,B2,B6andsoon)ProteinPhytohormoneIncreasingcropyieldandimprovingqualityNH4-NandNO3-NarethemajorsourcesofN.PlantcanalsoabsorbNO2–N,N2,aaandurea.NH4+、NO3-lowmolecularorganicNhighmolecularorganicNNO3-NuptakeisanactiveprocessNO3-NH4+aaProteinVacuole(Root)XylemShootXy
4、lem(Root)(NH4+aaProtein)AssimilationpathwayofNO3-inrootManyaffectingfactors:Light,Temperature,pH,andsoon.Whicharetightlyrelatedtonitratereductaseactivity.NitrateAssimilationMechanism:NO3-+8H++8e-NH3+H2O+OH-Twoseparateenzymes:Nitratereductase（硝酸还原酶,NR）reducingnitratetonitrite;
5、Nitritereductase（亚硝酸还原酶,NiR）reducingnitritetoammonia（氨）.NitratereductaseisacomplexenzymeNRcontainsseveralprostheticgroups:FAD,cytochrome,andmolybdenum.NRislocalizedinthecytoplasmandrequireseitherNADHorNADHPasanelectrondonor.NRhasahalf-lifeofonlyafewhours.NRispresentonlyinlowl
6、evelsinplantnotreceivingnitrate,butcanbereducedwithinafewhoursbytheadditionofnitrate.NiRhasalowmolecularweightandisassociatedinleaveswithchloroplastandinrootsmostlikelywithproplastide(前质体).Asarule,nitriterarelyaccumulatedinintactplantsundernormalconditions,becauseNiRispresent
7、atmuchhigherlevelsthanNR.Inmostplantspeciesbothrootsandshootsarecapableofnitratereduction.Theproportionofreductioncarriedoutineachlocationdependsonvariousfactors.AssimilationofammoniumAbsorptionofammoniumAbsorptionform:NH4+orNH3外界溶液NH3质膜细胞质NH4+H+AfterNH4+-Nwasabsorbedbyroots,
8、itwillberapidlyassimilatedintoaminoacidandamides,thenbetransportedto
