Atmospheric nitrogen dioxide (NO2) is ail environmental oxidant that is removed through direct uptake by foliage, but plant responses to this highly reactive gas are nor well understood at the molecular level. From NO2-exposed leaves of a woody azalea (Rhododendron mucronatum), we cloned two cDNAs (RmGLP1 and RmGLP2) for germin-like proteins (GLPs), a group of ubiquitous plant proteins that have been implicated in various plant physiological and developmental processes. Quantitative analysis of mRNA expression, together with immunoblotting data, showed that foliar exposure to NO2 caused a robust induction of these GLP-encoding genes. When produced in tobacco cell Culture, recombinant RmGLP2 was secreted into the apoplast, where it exhibited Superoxide dismutase activity. RmGLP1 and RmGLP2 represent the first examples of plant genes that are responsive to airborne NO2. These enzymes might have a potential role in extracellular defense mechanisms through attenuation of interactions between reactive nitrogen and oxygen species. (C) 2008 Elsevier Inc. All rights reserved.