More butenolides from plant-derived smoke with germination inhibitory activity against karrikinolide

Plant-derived smoke is known to play an important role in promoting germination in the post-fire environment, thereby stimulating regeneration of vegetation from the soil seed bank following a fire. Several compounds with germination promotory activity have been identified in recent years, with one such compound, 3-methyl-2H-furo[2,3-c]pyran-2-one (karrikinolide; KAR1) known to be highly active in promoting germination of many plant species at low concentrations. In contrast, a related compound, (5RS)-3,4,5-trimethylfuran-2(5H)-one, also found in plant-derived smoke, was shown to have an antagonistic effect against KAR1, resulting in lowered germination levels when tested on light-sensitive 'Grand Rapids' lettuce seeds which usually have high germination levels when treated with KAR1. Considering the combination of such types of compounds in smoke, there is the possibility of smoke having a dual regulatory mechanism to control post-fire seedling emergence. Here we report the identification of two structurally related butenolides from plant-derived smoke with germination inhibitory activity, namely 5,5-dimethylfuran-2(5H)-one and (5RS)-5-ethylfuran-2(5H)-one. In the germination test system using light-sensitive 'Grand Rapids' lettuce seeds, the 5,5-dimethylfuran-2(5H)-one showed similar levels of activity against KAR1 as previously observed with the (5RS)-3,4,5-trimethylfuran-2(5H)-one, whereas the (5RS)-5-ethylfuran-2(5H)-one was approximately 100 times less active.