Subject: what do fabaceae with the oxygen it bind because there is rhizobia?

fabaceae live in symbiose with rhizobia. The bacteria recieves N2 nad H2 
from the air and it produces NH4+. The only problem for the plant is, that it 
there is oxygen in the air and N2 "want" to produce N02. because there is 
this wish, the plant has to keep the oxygen out. fabaceae bind the  oxygen 
in its "skin".  But the plant dont need the oxygen in fact. It is in its skin and 
now? What does the plant do with it? 
thanks 
joelle

Re: what do fabaceae with the oxygen it bind because there is rhizobia?