WA researchers reveal smoke's 'phoenix factor'

Early Australian settlers evocatively dubbed fire 'the red steer' -- the untamed beast that rampaged through the bush, grazing it back to bare earth.

'Red prince' might have been more appropriate, because the smoke from bushfires delivers a potent chemical kiss that rouses the sleeping seeds of many native plants -- including many of Australia's most beauteous species -- to vibrant life.

For more than a decade, Australian native gardening enthusiasts have been soaking or irrigated the seeds of notoriously recalcitrant species with 'smoked' water solution to induce them to germinate, with no inkling as to the identity of the chemical or chemicals responsible.

Researchers from Perth's Kings Park at Botanic Garden, the University of Western Australia, and Murdoch University, led by UWA PhD student Gavin Flematti, have now identified the mystery molecule that breaks seed dormancy in many species, and turbo-charges seedling growth in many others.

It's a simple arrangement of two carbon rings with three oxygen atoms and a methyl group, from a class of molecules called butenolides. A by-product of the combustion of cellulose and other organic compounds common to the tissues of all plants, the butenolide delivers its wake-up call to deeply dormant native plant seeds at a concentration of only parts per trillion -- equivalent to one teaspoon in three Olympic swimming pools' worth of water.

Lost in the chemical forest

In the past decade, research groups in South Africa, Germany and California, as well as the Perth team, repeatedly became lost in the chemical forest of some 4000 compounds in smoke as they sought the elusive 'phoenix factor'.

They collaborated extensively, but Dixon says his team eventually took the potentially lucrative prize by playing its hunches right, and never assuming that the phoenix factor would be a major component of bushfire smoke.

Dixon said some African tribes traditionally used smoke to germinate the seeds of native red rice, and later, maize, but it was a South African scientist, Dr Johannes de Langer, who initiated the quest for the phoenix factor.

South African botanists were dismayed when fire ravaged a reserve protecting the last known stand of a rare native plant, Audonia capitata, but were delighted a few weeks later when seedlings germinated en masse from the blackened ground.

South African researchers had unsuccessfully experimented with heat treatments to break dormancy in Audonia seeds, and had also added bushfire ash to seed-raising mixes. After the Audonia mass germination, de Langer realised that smoke, as well as a heat, was probably involved in breaking seed dormancy.

Dixon learned of the smoke research when he and a colleague visited the Kirstenbosch Botanic Gardens in Pretoria.

Like Audonia and many other beautiful flowering plants of South Africa's fire-adapted fynbos heathlands, some of the most spectacular flowering plants of the Western Australian heathland flora are extremely difficult to germinate. They include kangaroo paws (Anigozanthos spp), smokebushes (Conospermum spp), feather flowers (Verticordia spp) and 'Yellow Bells' (Geleznowia verrucosa), a species prized by the cut flower trade, have dormancy mechanisms.

Because of the difficulty -- or impossibility, in the case of Geleznowia -- of germinating the seed, the cut flower industry harvests flowers from the wild, placing pressure on wild populations. Cutting of wildflowers also increases the risk of disseminating the devastating root-rot fungus Phytophthora cinnamomi through highly susceptible plant communities.

Heat and smoke

Kings Park researchers had also explored the use of heat to induce germination, with limited success. "It dawned on us that maybe we had overlooked smoke as the key factor in mass germination after bushfires in Australia," Dixon says.

Initially, they failed to replicate the germination results obtained by South African researchers, but then discovered that most Australian species required much higher smoke concentrations to break dormancy.

"Once we worked that out, we really cleaned up [germination difficulties] on a great slab of the Australian flora that comes up after bushfires," Dixon says. "It's not just the WA flora -- it doesn't matter whether you're in the Kimberley, the desert, or in the Tasmanian alps, smoke will germinate a vast range of Australian plant species."

They include long-lived woody species like Hakea, Banksia and the native conifer Actinostrobus, which retain their seed in cones or woody capsules for years. These 'bradysporous species' are killed by bushfire, which opens their seed capsules, to broadcast the seed into the ash bed.

The molecule also increases germination rates in some vegetables, including lettuce and celery, and Dixon's team has shown it also boosts germination of the difficult-to-grow herbal remedy, Echinacea.

Chemists working with Dixon's team took almost a decade to sift through the chemical cocktail in smoke, using high-pressure liquid chromatography and mass spectrometry.

It became clear that the phoenix factor was not just present in bushfire smoke, but in all smoke from burning plant materials -- even lettuce.

On the flank of one of the major peaks in the MS spectrum of smoke from filter paper, which is almost pure cellulose, Dixon's team spotted a "tiny blip".

They purified the compound, which dissolved readily in water, and soaked seeds of 20 of the most resolutely dormant species in the WA flora, including Geleznowia, kangaroo paws, trigger plants (Stylidium), guinea flower (Hibbertia) and feather flowers (Verticordia). All germinated rapidly, and en masse.

Expriments have shown that the treatment does not increase the permeability of the seeds to water. Dixon says one action of the butenolide appears to increase the receptivity of the seed to internal reserves of gibberelic acid.

Growth turbocharger

Very recently, the WA researchers have shown that, even in species that do not require smoke germination, such as banksias and eucalypts, a dose of butenolide turbocharges seedling growth.

Dixon says the compound appears to activate the seedling's gibberelin growth-hormone pathways, providing a growth surge that capitalizes on the nutrient-rich environment created by bushfire.

Dixon and his colleagues have previously shown that concentrated smoke solutions also stimulate mass-germination when sprayed onto unburned native vegetation communities -- typically, species richness in the sprayed areas doubles, relative to control areas sprayed with water alone.

However, it is too expensive to spray with smoke water at the concentration required to stimulate mass germination. Dixon says butenolide can be synthesised cheaply, and its remarkable potency at very low concentrations, makes it feasible for broad-scale use.

Conservation authorities are often reluctant to burn plant communities containing rare and endangered species to stimulate generation, because of the risk of igniting wildfires, or losing fire-sensitive species.

Farmers are also reluctant to burn remnant plant communities on their land because they value their aesthetic value, and they are refuges and food sources for native wildlife.

By spraying these communities with butenolide, either from the ground or by air, dormant seeds of rare species hidden in the litter layer could be stimulated to regnerate without sacrificing the existing vegetation -- with a good chance that the treatment would stimulate the germination of vanished or even new species that have disappeared because of the suppression of wildfire.

Dixon's group believes butenolide sprays could also be used to enhance germination of native seeds broadcast to stabilise wind-blown mining waste dumps, or to regenerate plant communities on restored mining sites.