A Smoky Beginning for Plants
It's well-known that some plants depend on bush fires to make their seeds germinate, but how? Gavin Flematti researches this question at the University of Western Australia and he explained to Chris how he's discovered the chemical in smoke that's responsible.
Gavin - It's been known for a number of years that fire in a landscape, once that fire has gone through when the next rain has come along, you get this sudden regeneration of growth of the native species. And some researchers at South Africa worked out that there were actually, chemicals in the smoke that were responsible for this effect. So, I sort of came on board and we were looking at trying to work out what the actual chemical compounds were that were responsible for this effect.
Chris - So, when you say something in the smoke was making this happen, it's not just that you burn everything out, the competition drops and some seeds happen to be there that survived the burning and they grow. There's actually an active process which is triggering seeds to grow, but only when there's smoke around.
Gavin - Yeah, that's right. The researcher in South Africa, Johannes de Lange, he was trying to germinate this species that was only ever seen after a fire, and he was trying everything he could think of to get it to germinate and it just wouldn't. So then, he smoked a small area out in the landscape there and came back sort of 12 months later, and lo and behold that species are germinated. So, he worked out that there was something actually in the smoke that was responsible for this effect.
Chris - So, how did you attack that problem? What approach did you take to try to work out what was going on?
Gavin - Well basically, I mean, Johannes de Lange had worked out that if you bubble a smoke through water, you got this product called smoke water and that was active on the seeds as well. So, we started with that. We then would mix that with organic solvents and try and extract that compound out of the solution, and then just lots of chromatography. So, we use a lot of ways to try and separate compounds until we're able to pin it down to one in particular compound.
Chris - So, you're growing seeds that are dependent on whatever this smoke is, to grow and then mixing them with different fractions of what had been bubbled through the water. So, you separated into all the different chemicals until you've got the one that does it.
Gavin - Yeah, well I mean, smoke contains out of 4,000 compounds it was a big task. So, it was multiple steps. Basically, we would just try and simplify the mixture to start with and as you say, take a lot of fractions, test those with the particular species. We were actually using a particular lettuce species that would germinate fine in the light, but in the dark, you'd only get about 30% or 40% germination. But then you'd give it the smoke compound, that would then bring that back up to 100%. The reason we used that, there was a quick turnaround of results, only 2 days whereas some of the natives take up to 6 weeks.
Chris - What are the chemicals that do it?
Gavin - We identified a compound. It belonged to a class of compound called butenolides and we've given it sort of the trivial name of Karrikinolide.
Chris - How does it work?
Gavin - Well, it's a very good question. We're still in the process of trying to work that out. We're now working with molecular biologists and geneticists at UWA and they're really trying to dissect what the key proteins are that it's interacting with. I mean, one way they're looking at this is they're creating mutated plants that don't respond to the compound. So, this particular plant we used Arabidopsis is like the lab rat of the plant world and we're lucky enough that it responds to our compound. And so, what they've done is now transform the plants so they don't respond, and then we're looking for what the key protein that's missing. So, it's quite a neat way of doing it.
Chris - What about this chemical makes it particularly appropriate to do that job of triggering that plant to germinate. Because if there are 4,000 chemicals in smoke as you've said, why did the plants pick that one?
Gavin - We're not sure. I mean, it's got some structural similarities to some other plant growth promoters, but we still haven't cracked how it's actually working yet.
Chris - Apart from being academically really interesting to know what it is that triggers things to grow off to burning. Will this be useful in any way? Could you use it to sustain, support, or trigger growth or for conservation efforts?
Gavin - Yeah, well our goal at the moment is trying to get a formulation that we can use in the field. At the moment, when we spray it on the ground as a synthetic material, it just don't seem to have the same effect as when we smoke an area and there's a whole range of reasons for that. It might be prone to oxidation, it seems to have some UV instability. But when it's present in the smoke mixture, there's other compounds there that are acting as sunscreens or anti-oxidants that are helping to stabilise it. So, that's part of the big project we have at the moment. It's trying to work out, well how can we stabilise this and formulate it so it's effective.