Karrikins (KAR) are butenolide molecules produced during wildfires in smoke and deposited on soil surface. They are absorbed by seeds and activate germination. Strigolactones (SL) are different butenolide plant hormones with tricyclic lactone, that influence root branching leaf shape and senescence. KAI2 and D14 are paralogous alpha/beta hydrolase receptors respectively for KARS and SLs they belong to the RsbQ-like family. KAI2 (KARRIKIN-INSENSITVE-2) and D14 (DWARF14) are both receptors and enzymes.
It is well known that burning of vegetation stimulates new plant growth and landscape regeneration. The discovery that char and smoke from such fires promote seed germination in many species indicates the presence of chemical stimulants. Nitrogen oxides stimulate seed germination, but their importance in post-fire germination has been questioned. Cyanohydrins have been recently identified in aqueous smoke solutions and shown to stimulate germination of some species through the slow release of cyanide. However, the most information is available for karrikins, a family of butenolides related to 3-methyl-2H-furo[2,3-c]pyran-2-one. Karrikins stimulate seed germination and influence seedling growth. They are active in species not normally associated with fire, and in Arabidopsis they require the F-box protein MAX2, which also controls responses to strigolactone hormones. We hypothesize that chemical similarity between karrikins and strigolactones provided the opportunity for plants to employ a common signal transduction pathway to respond to both types of compound, while tailoring specific developmental responses to these distinct environmental signals.
Karrikins are a chemically defined family of plant growth regulators discovered in smoke from burning plant material. Karrikins are potent in breaking dormancy of seeds of many species adapted to environments that regularly experience fire and smoke. The recent discovery that karrikins trigger seed germination and control seedling growth in taxa that would rarely experience fire indicates that their significance could extend far beyond fire ecology. This is exemplified by new studies showing that seeds of Arabidopsis thaliana respond sensitively and specifically to karrikins in smoke. These exciting discoveries might be explained if karrikins are produced in the environment by processes other than fire,
such as by chemical or microbial degradation of vegetation in response to disturbance of the soil or removal of the plant canopy. Another hypothesis is that plants contain endogenous karrikins that function naturally in the control of seed germination and that species from fire-prone habitats have evolved to respond also to exogenous karrikins. A variant on this hypothesis is that karrikins mimic
endogenous plant hormones such as terpenoids that control seed germination. The evidence for these hypotheses is discussed, but whatever the explanation karrikins are now firmly established as an important family of naturally occurring plant growth regulators.
Title: Identification of alkyl substituted 2H-furo[2,3-c]pyran-2-ones as germination stimulants present in smoke Flematti GR, Ghisalberti EL, Dixon KW, Trengove RD Ref: Journal of Agricultural and Food Chemistry, 57:9475, 2009 : PubMed
The butenolide, 3-methyl-2H-furo[2,3-c]pyran-2-one (1), is a major compound in smoke responsible for promoting the seed germination of a wide range of plant species. We now report the structure of five alkyl substituted variants of 1 that are also present in smoke. The concentrations of these analogues, as well as that of 1, in a typical smoke-water solution have been determined using high-performance liquid chromatography (HPLC) purification followed by gas chromatography-mass spectrometry (GC-MS) analysis. The analogue, 3,5-dimethyl-2H-furo[2,3-c]pyran-2-one (3), was identified at levels that indicate that it is a contributor to the overall germination-promoting activity of crude smoke extracts.
