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					Nitrogen has to be reduced

NH3/NH4+          ammonia/um         -3
N2                dinitrogen         0
N2O               nitrous oxide      +1
NO                nitric oxide       +2
NO2-              nitrite            +3
NO2               nitrogen dioxide   +4
NO3-              nitrate            +5



                                     + N fertilizer
- N fertilizer
                                          nitrification


               denitrification


Soil nitrate is lost by denitrification

Ammonium is lost by nitrification
Examples of N
containing compounds
Comparison
of metabolism
                     The nitrogenase enzyme




The metal cofactors are oxygen labile
   Symbiotic N fixation


 N-deficiency induces nodules (new organ)




               3X pea                              7X pea

See table 16.4 for specific symbiosis of legumes
                                                   New organ is
                                                   produced

Communication between bacteria and plants contributes to specificity
                     symbiosomes




Bacteria also differentiate to establish symbiosis
         ATP production at low partial pressure of O2




High affinity cytochrome oxidase
Leghemoglobin
O2 permeability barrier
  GS-GOGAT cycle

                          Asn, Gln, ureides
                          transported through xylem




diCOOH acid in, gln out
Purine synthesis is turned on by NH3
Purine degradation is developmentally determined
    Nitrate uptake and reduction




Taken up in roots but also leaves

                             Transport driven by H+ gradient
                             H+ gradient established by ATP hydrolysis
Regulation of nitrate uptake depending on availability
Identification of a
mutant in nitrate uptake



Chlorate resistant plant
 After uptake, nitrate is reduced to nitrite
                     first committed step
 NO3- + NADPH + H+                  NO2- + NADP+ + H2O
 Nitrate reductase is in cytosol
 has heme, FAD and MoCo
 Dimers/tetramers




-10 mV                -272 mV
          -160 mV
 Domains combined to form enzyme?
Nitrite is then reduced to ammonia in the plastid

 NO2- + 6 Fdred + 8 H+           NH4+ + 6 Fdox + 2 H2O

NiR is regulated coordinately with NR at tx level


From photosynthesis or
from NADPH in
colorless plastids   NADPH + 2 Fdox         NADP+ + 2 Fdred + H+




 60-70 kDa with two domains

				
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