
TY  - JOUR
A1  - Shearer, G 
A1  - Kohl, DH 
T1  - Natural <sup>15</sup>N Abundance of NH<sub>4</sub><sup>+</sup>, Amide N, and Total N in Various Fractions of Nodules of Peas, Soybeans and Lupins
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 1989
VL  - 16
IS  - 4
SP  - 305
EP  - 313
KW  - 
UR  - https://doi.org/10.1071/PP9890305 
N2  - Nodules of certain N2-fixing root nodules are substantially enriched in 15N compared with non-nodular tissues. This enrichment usually resides largely within bacteroids. Isotope discrimination associated with export of ammonia(um) from the bacteroid would result in 15N enrichment of NH4+ within bac- teroids. Bacteroid protein synthesis from this pool of 15N enriched NH4+ would then account for enrichment of the bacteroids. Measurements of 15N abundances of total N and free NH4+ in nodule fractions from lupins (Lupinus luteus), soybeans (Glycine max) and peas (Pisum sativum) showed this was not the case. With the inocula used in experiments reported here, lupin and soybean nodules were enriched in 15N, while pea nodules were not. There was no correlation between 15N abundances of NH4+ and total N in the nodule fractions (r= 0.445, P> 0.2). We conclude that isotope discrimination associated with ammonia(um) transport does not explain the 15N elevation of lupin and soybean nodules. We also conclude, on the basis of the large isotope effect for the equilibrium between NH4+ and NH3, that most of the ammonia(um) is exported from bacteroids as NH4+ rather than NH3.    We also measured the 15N abundance of free amide N. There was a strong correlation between 15N abundances of free amide N and total N in nodule fractions (r=0.924, P<0,001), suggesting that amide N is a significant source of N to the amino acid pools from which proteins are synthesised. 
ER  -

