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

Both the California chaparral species, Emmenanthe penduliflora Benth. ( Hydrophyllaceae ), and a tobacco native to the Great Basin Desert of south-western Utah, Nicotiana attenuata Torr. ex Wats. ( Solanaceae ), germinate in response to component(s) of wood smoke. Nitrogen oxides (NO and NO 2 ), in amounts produced by a fire, have been proposed to be germination signals for E. penduliflora . We examined the germination response of dormant seeds of E. penduliflora and N. attenuata to aqueous solutions of smoke adjusted to different pHs, and two NO donors [sodium nitroprusside (SNP) and S -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, NO 2 – could not be detected in aqueous smoke extracts derived from combusted cellulose or wood. Therefore, unidentified cellulose combustion factors, rather than NO x , are likely to be the ecologically relevant germination signals.