What are karrikins and how were they 'discovered' by plants?

© 2015 Flematti et al. Karrikins are a family of compounds produced by wildfires that can stimulate the germination of dormant seeds of plants from numerous families. Seed plants could have 'discovered' karrikins during fire-prone times in the Cretaceous period when flowering plants were evolving rapidly. Recent research suggests that karrikins mimic an unidentified endogenous compound that has roles in seed germination and early plant development. The endogenous signalling compound is presumably not only similar to karrikins, but also to the related strigolactone hormones

Burning vegetation produces cyanohydrins that liberate cyanide and stimulate seed germination

Cyanide is well known for its toxicity towards living organisms. Many plants use cyanide as a defensive agent against herbivores, releasing it through the enzymatic hydrolysis of endogenous cyanogenic compounds. At low concentrations, cyanide has been proposed to have a regulatory role in many plant processes including stimulation of seed germination. However, no ecological role for cyanide in seed germination has been established. In the present study, we show that burning plant material produces the cyanohydrin, glyceronitrile. We also show that, in the presence of water, glyceronitrile is slowly hydrolysed to release cyanide that stimulates seed germination of a diverse range of fire-responsive species from different continents. We propose that glyceronitrile serves as an ecological store for cyanide and is an important cue for stimulating seed germination and landscape regeneration after fires