Synthesis of tricyclic butenolides and comparison their effects with known smoke-butenolide, KAR1

Plant-derived smoke - butenolide, called at present karrikin 1 (KAR(1)) is known as an important inductor of seed germination and seedling growth. In this study, tricyclic butenolides were synthesized and their effects on germination of dormant and non-dormant Avena fatua caryopses were compared, as were also their effects versus those of KAR(1) on seedling growth. KAR(1) was found to be most effective and to completely remove dormancy. Butenolides, rac-8 and (S)-8a, showed a low stimulatory effect on germination of dormant caryopses, visible only when applied at very high concentrations. These compounds used at concentrations 100 times those of KAR(1) similarly increased the speed of germination and vigor of non-dormant caryopses. Likewise, growth of coleoptiles and their fresh weight were increased by KAR(1) as well as by rac-8 and (S)-8a to a similar value. KAR(1) and rac-8 were more effective than (S)-8a in increasing root growth. The results shown indicate that the presence of an aromatic ring in the absence of methyl group at C3 induced a much lower, or a similar, effect on germination of dormant and non-dormant Avena fatua caryopses and seedling growth compared to KAR(1), but only when used at much higher concentrations. The simultaneous presence of a methyl group at C3 and an aromatic ring in the compound rac-7 exerted only a slight effect on the root growth.