This is a nice little study in PNAS. It is nice for a few
reasons. For one, it is the sort of thing that drives
conservatives crazy, for it seems to be a highly detailed study of
something useless. Two, it could turn out to be pretty
useful. Three, when I searched ScienceBlogs for “karrikin,” I got
zero hits. Fourth, when I search Wikipedia for “karrikin,” I got
zero hits. So it is about time someone started talking about
these chemicals. Plus, “karrikin” is a cool word.
“Karrikin” is the Noongan
word for “smoke.” Karrikins comprise a class of chemicals
found in smoke from burning plant matter. It has been known for a
long time that smoke from brush fires can stimulate the germination of
some kinds of seeds. In fact, persons who are trying to germinate
difficult-to-start seeds, will sometimes use products derived from
smoke, in an effort to get the seeds to germinate.
1. Partial structural similarity between
the karrikin family of plant growth regulators and
Researchers in Australia have been studying this for a few years, at
Dr Nelson, a researcher at the Australian Research Council (ARC) Centre
of Excellence in Plant Energy Biology, at The University of Western
Australia, is investigating how it is that some plant seeds are
triggered to germinate after exposure to smoke…
Dr Nelson said fires played a major role in shaping the Australian bush.
“Even though the landscape looks devastated to us after a bushfire, it
is quickly covered by a flush of new growth,” he said.
“For the seeds of many native Australian species, the smoke from a fire
is the trigger to wake up and take advantage of the newly available
resources. Understanding this phenomenon could have major impacts on
conservation efforts and agriculture.”
Although smoke is a complex mixture of thousands of different
compounds, recent work at UWA and Perth’s Kings Park laboratories was
able to identify a single ‘smoke alarm’ component that snaps seeds out
Now, it turns out that karrikins have an additional role:
Karrikins are a class of seed germination stimulants identified in
smoke from wildfires. Microarray analysis of imbibed Arabidopsis
thaliana seeds was performed to identify transcriptional responses to
KAR1 before germination. A small set of genes that are regulated by
KAR1, even when germination is prevented by the absence of gibberellin
biosynthesis or light, were identified. Light-induced genes, putative
HY5-binding targets, and ABRE-like promoter motifs were overrepresented
among KAR1-up-regulated genes. KAR1 transiently induced the light
signal transduction transcription factor genes HY5 and HYH. Germination
of afterripened Arabidopsis seed was triggered at lower fluences of red
light when treated with KAR1. Light-dependent cotyledon expansion and
inhibition of hypocotyl elongation were enhanced in the presence of
germination-active karrikins. HY5 is important for the Arabidopsis
hypocotyl elongation, but not seed germination, response to karrikins.
These results reveal a role for karrikins in priming light responses in
the emerging seedling, and suggest that the influence of karrikins on
postfire ecology may not be limited to germination recruitment.
thaliana is mouse-ear cress, a fairly useless plant.
Why study it? It has been studied intensively as a model
organism. It is small and reproduces rapidly, making it fairly
easy to study. It is sort of like studying fruit flies.
Even though the model organism itself is not useful, it provides a
standardized and well-understood context for basic science research.
Granted, the study leads to a fairly limited conclusion: “…suggest
that the influence of karrikins on postfire ecology may not be limited
to germination recruitment.” Still, the more we understand about
how plants grow, the better. If we can find ways to get higher
rates of germination and growth of useful plants, that could be