Smoke's Plant-Boosting Powers Found

Fire can be destructive and devastating, but it also helps plants grow.

Scientists are zeroing in on the chemicals in smoke that stimulate seeds to sprout. By tapping into the powers of fire, scientists hope to get onions, tomatoes and other food crops to grow more reliably, more quickly and in more challenging environments. But that’s not all.

"By applying these molecules, I believe we can improve farming, we can improve weed control, we can improve revegetation of the environment after destructive mining, and we could definitely improve the stress tolerance of plants," said botanist Johannes van Staden, director of the Research Centre for Plant Growth & Development at the University of KwaZulu-Natal in South Africa. "My personal belief is that these molecules, in years to come, will revolutionize agriculture."

People have known for a long time that plants grow better after fire sweeps through. In some cases, species that were thought to be extinct have reappeared after burns. Still, it has been difficult to pinpoint exactly how fire sparks growth, van Staden said, because close to 4,000 chemical compounds occur naturally in smoke.

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Beginning in 1990, van Staden spent 14 years narrowing the search down to one type of molecule, called butenolides, and he published a paper about them in 2004 the South African Journal of Botany.

Since then, the race to find clarity in smoke has only grown more intense. Scientists now know that there is a whole family of butenolides, also called karrikins. These molecules get inside seeds and help them grow. ("Karrik" is an aboriginal term for smoke). But the story does not end there.

Alongside karrikins, van Staden's group has recently found, smoke contains a molecule that prevents karrikins from working. This inhibitor molecule gets into seeds, too. But unlike karrikins, the inhibitor washes away in the rain. Once it's gone, seeds can sprout.

"I'm 100 percent convinced that this little molecule is the one that tells the seed, 'Look, you can germinate now because there's enough water,'" van Staden said. "It's all very, very preliminary, and we have to do an awful lot of work on this. But I think it opens up one of the most wonderful systems."

In experiments, van Staden's group has found that smoke's wondrous compounds help seeds grow. They help plants reach maturity faster. And they allow plants to withstand all sorts of stresses, including heat, cold, drought and heavy metal pollution. The molecules work on maize, okra, tomatoes, onions, dry beans and more.

Smoke compounds are not toxic to humans, and van Staden imagines a day when farmers will be able to use man-made versions of these molecules to produce multiple rounds of crops in the same growing season, even when conditions are less than ideal. As the global climate continues to change, sub-optimum conditions are likely to become more common.

Molecular biologist Steven Smith suspects that applications for smoke compounds will be more specialized. He imagines, for example, using karrikins to stimulate dormant weeds to sprout, providing an opportunity to wipe them out all at once. They could also help stimulate long-dormant seeds from seed banks, he added, or help plants grow in areas polluted by mining.

Smith, who is part of a group at the University of Western Australia in Perth that's in competition with van Staden's group, also has a different view of how karrikins work. In the Proceedings of the National Academy of Sciences last month, his team reported evidence that the molecules make seeds more sensitive to light.

"It kind of primes them for the new environment," he said. "Once a fire has gone through, it changes the light quality because you lose the canopy of leaves, and the surface of the soil becomes blacker."

As scientists continue to investigate the details, the biggest challenge for now is finding cheaper and more efficient ways to synthesize smoke-inspired plant helpers.

"We've still got some time to go," Smith said. "There is a fair bit of chemistry to be done."