Abstract
Atmospheric NOx, which includes nitric oxide and nitrogen dioxide, is usually regarded to act as N source or to exert detrimental effects on plants. No reports on its signaling effect, however, have so far been reported. In this study we cultured plants (Nicotiana plumbaginifolia) under the natural light for several months in the air "polluted" with 15N-labelled NOx (100 to 200 ppb) and in the "clean" air with no or very low level of NOx (<5 ppb). We have discovered that the biomass yield, element contents, total free amino acids and crude proteins were almost doubled in the plants cultured in the polluted air than the ones cultured in the clean air. Isotopic mass spectrometry showed that the nitrogen derived from NOx made only a negligible contribution in the total nitrogen of plants. Therefore, the present findings imply that urban NOx "pollution" is a plant vitalization signal.
