Nitrogen metabolism of Spirodela oligorrhiza : I. Utilization of ammonium, nitrate and nitrite

Spirodela oligorrhiza grown in axenic culture was able to use either ammonium, nitrate, or nitrite as sole source of nitrogen, although the morphology of the plants was affected. Plants utilizing ammonium contained higher levels of NH4, arginine, asparagine and glutamine than did those utilizing NO3, whereas concentrations of other amino acids were similar.The utilization of NH4 inhibited that of NO3 by inhibiting, at least partially, NO3 uptake, and by inhibiting almost completely the reduction of NO3 to NO2. NO2 also inhibited the utilization of NO3. NH4 and NO2 were taken up and assimilated simultaneously when they were supplied together in the medium.