Nitrate, but not nitrite, derived from nitrogen dioxide accumulates in Arabidopsis leaves following exposure to N-labeled nitrogen dioxide.

It is known that when plant leaves are exposed to exogenously applied nitrogen dioxide (NO), nitrogen derived from NO is reduced to amino acid nitrogen. However, whether this is the sole metabolic fate of exogenously applied NO is unclear. In this study, Arabidopsis leaves were exposed to 4 ppm N-labeled NO for 4 h in light, followed by capillary ion analysis and elemental analysis-mass spectrometry with an elemental analyzer connected directly to a mass spectrometer. We found that leaf cells exposed to N-labeled NO accumulated a large amount of N-labeled nitrate. Neither N-labeled nitrite nor endogenous nitrite was present in exposed leaves. It is likely that exogenously applied NO is first converted to nitrite, and that nitrite is oxidized to nitrate in Arabidopsis leaf cells. The complete disappearance of nitrite derived from exogenously applied NO and endogenous nitrite supports this mechanism.