Is ‘NO’ news good news? Nitrogen oxides are not components of smoke that elicits germination in two smoke-stimulated species, Nicotiana attenuata and Emmenanthe penduliflora

Abstract

Both the California chaparral species,Emmenanthe pendulifloraBenth. (Hydrophyllaceae), and a tobacco native to the Great Basin Desert of south-western Utah,Nicotiana attenuataTorr. ex Wats. (Solanaceae), germinate in response to component(s) of wood smoke. Nitrogen oxides (NO and NO2), in amounts produced by a fire, have been proposed to be germination signals forE. penduliflora. We examined the germination response of dormant seeds ofE. pendulifloraandN. attenuatato aqueous solutions of smoke adjusted to different pHs, and two NO donors [sodium nitroprusside (SNP) andS-nitroso-N-acetylpenicillamine (SNAP)]. The smoke solutions, at pH 4 or 5, induced the maximum germination response. Aqueous solutions of SNP and SNAP, releasing NOx as high as 42 μM, had no effect on germination. Additionally, NO2–could not be detected in aqueous smoke extracts derived from combusted cellulose or wood. Therefore, unidentified cellulose combustion factors, rather than NOx, are likely to be the ecologically relevant germination signals.