Nitrate, but not nitrite, derived from nitrogen dioxide accumulates in Arabidopsis leaves following exposure to 15 N-labeled nitrogen dioxide

Abstract

It is known that when plant leaves are exposed to exogenously applied nitrogen dioxide (NO 2 ), nitrogen derived from NO 2 is reduced to amino acid nitrogen. However, whether this is the sole metabolic fate of exogenously applied NO 2 is unclear. In this study, Arabidopsis leaves were exposed to 4 ppm 15 N-labeled NO 2 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 15 N-labeled NO 2 accumulated a large amount of 15 N-labeled nitrate. Neither 15 N-labeled nitrite nor endogenous nitrite was present in exposed leaves. It is likely that exogenously applied NO 2 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 2 and endogenous nitrite supports this mechanism.