Abstract
Our previous study showed that approximately one-third of the nitrogen of 15N labeled NO2 taken up into plants was converted to a previously unknown organic nitrogen (hereafter designated UN) that was not recoverable by the Kjeldahl method. All of the 12 plant species were found to form UN derived from NO2 (about 10–30% of the total nitrogen derived from NO2). The UN was formed also from nitrate nitrogen. Thus, UN is a common plant metabolite. Our studies using transgenic plants suggest that nitrite and other reactive nitrogen species (RNS) are involved in the formation of the UN, and that the UN-bearing compounds are metabolizable. The UN-bearing compounds identified to date in the extracts of the leaves of Arabidopsis thaliana fumigated with NO2 include a Δ2-1, 2, 3-thiadiazoline derivative and 4-nitro-β-carotene. Here, we will discuss on the metabolic and physiological relevance of the UN-bearing compounds.
