Can GM trees please?

Scientists modify poplars to reduce hazardous compound production.

The Arizona poplar plantation during the first year of growth.

D.J.P. Moore, University of Arizona.

By Ian Connellan

Strange as it may seem, some trees are not always environmentally friendly.

Poplars, for example, produce isoprene in their leaves in response to climate stress such as high temperatures – and increases in this compound can lead to higher levels of airborne particle production, higher rates of ozone in the troposphere and longer-lasting methane.

That’s significant when you consider that poplar plantations are large and valuable. In the past 15 years the total area globally has more than doubled to 9.4 million hectares – roughly the size of Hungary.

With this in mind, a team of US and German scientists is exploring whether genetic modification of poplars can reduce harmful emissions while maintaining their productivity.

And the answer, they report in the journal Proceedings of the National Academy of Sciences, appears to be yes.

Three years of trials at plantations in the US states of Oregon and Arizona found that trees whose isoprene production was genetically suppressed did not suffer any ill effects in terms of photosynthesis or "biomass production".

They were able to make fuel and grow as well as trees that were producing isoprene.

Steve Strauss, a forest biotechnologist from Oregon State University, suggests a couple of possible explanations.

One is that, without the ability to produce isoprene, the modified poplars appear to be making "compensatory protective compounds".

Another is that most of the trees' growth takes place during cooler times of the year, so heat stress, which triggers isoprene production, likely has little effect on photosynthesis at that time.

“In Arizona, where it’s super hot, if isoprene mattered to productivity, it would show up in a striking way, but it did not,” he says. “Plants are smart – they’ll compensate and do something different if they need to.”

Strauss and colleagues used RNA interference in the study. RNA – ribonucleic acid – transmits protein coding instructions from each cell’s DNA, which holds the organism’s genetic code.

“RNA interference is like a vaccination – it triggers a natural and highly specific mechanism whereby specific targets are suppressed,” he says.

In this study, it was the isoprene production being suppressed.

The fact that poplars can be cultivated to reduce environmental impacts without diminishing productivity “gives us a lot of optimism”, says co-author Russ Monson, from the University of Arizona.

“We’re striving toward greater environmental sustainability while developing plantation-scale biomass sources that can serve as fossil fuel alternatives.”

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