Smoke reveals mystery of how seeds sprout

PhD student Gavin Flematti and colleagues from the University of
Western Australia published their research online today ahead of print
publication in the journal Science.

Many Australian plants, like the acacia, depend on the heat from fires
to crack open their seeds before they can germinate.

But bushfire smoke can play an even bigger role in seed germination.
So, since the 1990s scientists have been trying to identify which of
the thousands of chemicals in bushfire smoke is the crucial trigger.

Now an Australian team has found that chemical, after sifting through
about 4000 others in plant-derived smoke.

The chemical, a butenolide, is new to science and is made up of a
heterocyclic ring of carbons, and other atoms. It also comes from a
class of compounds never before found in plants or animals.

Team member Dr Kingsley Dixon, director of the Kings Park and Botanic
Garden in Western Australia, said the finding represented 11 years of
work.

"It's been so long coming that we just look at the amazing results and
think, what a lot of work."

Dixon said the team was one of several international teams searching
for the active ingredient.

"It was the proverbial needle in a haystack," said Dixon. "Being
Australian we decided to be maverick and look at a different approach
using unique separation chemistry."

This involved separating the chemicals with a syringe containing an
ion-exchange resin. Depending on its composition the resin removed
growth promoting, growth suppressing or neutral chemicals.

The researchers then found they had a much smaller pool of chemicals to
search through. They then isolated the chemical.

Flematti said this was the first time the active ingredient in smoke
that assists germination had been identified.

"We have not only identified it, we isolated it and synthesised it to
confirm its activity," he said.

The chemical germinates seeds from many types of plants, Flematti said,
not just fire-dependent species.

For example, the researchers tested it on lettuce seeds, because of
their quick germination time.

In the test group, 90% of the lettuce seeds germinated when the
chemical was added, compared to 40% in the control group.

The researchers also tested native Australian and North American
species. In the wild, less than 5% of the seeds of some native
Australian species germinate. With the chemical, this increased up to
80%.

But Flematti said the researchers didn't yet know how the chemical acts
on the seed and which part of the seed responds to the chemical.

Although heat from bushfires also helps seed germination in some
species, Flematti said smoke was a "more universal cue".

It also allows seeds to germinate in the seed bank, fallen seeds buried
quite deep in the soil.

"When a fire goes through there is a lot of heat on the surface, but
that doesn't get down to the seed bank below," he said.

But when it rains, the rainwater filters the smoke that has settled on
the soil surface down below.

According to Flematti the chemical could find uses in land restoration,
including rehabilitation of degraded land and land damaged by mining
activities.

"Mining companies have an obligation to replace the native species that
were wiped out and that isn't always easy," he said. "Some are very
difficult to germinate."

Flematti also thought it could eventually find use in horticultural and
agricultural areas and even in the cut-flower industry, which values
native Australian flowers such as fire-dependent banksias and kangaroo
paw.

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