Plant Gas – From Attracting Moths to Influencing The Climate

Plants “Stink”

One of the really cool things about plants, which I think most people don’t realize, is that they emit many kinds of volatile organic compounds (VOCs).

Some of these VOCs we can smell, such as flower fragrances and pine scents. But many, such as the plant hormone ethylene, may either have no odor to us or be produced in such vanishingly small amounts that we cannot detect them. But some machines can…

Thanks to such machines (see Ref. 1 below, for example), plant scientists can routinely detect and analyze trace gases (down to 1 part per billion) released by plants under different conditions, not only in the lab, but also under natural conditions in the field. This has led to many new insights regarding plant-plant and plant-insect communication, as I’ve mentioned in previous posts, such as “Talking” Plants.

Collectively, plant VOCs may even have effects on the Earth’s atmosphere.

Two research reports regarding very different aspects of plant VOCs have recently caught my eye.

Like a moth to a “burning bush”?

Some naturally-produced plant VOCs have been known for some time to act as a defense against insect herbivores (see here, for example). But a report in the 25 February, 2014, issue of Nature Communications (please see Ref. 2 below) adds a whole new dimension to plant-to-insect chemical signaling.

Briefly, a team of scientists have genetically-engineered tobacco plants to express an array of enzymes – using a combination of plant and insect genes – that collectively produce sex pheromones that attract moths. (One of the plant genes came from Euonymus alatus, a.k.a., “burning bush”.)

At this point, you may be asking “Why?”.

Answer: From Ref. 2 below – “Pheromones are environmentally friendly alternatives to traditional pesticides for the control of insect pests and indeed synthetic pheromones are produced in large amounts for this purpose. Current standard approaches to pheromone synthesis either require the use of hazardous chemicals or may result in the production of hazardous waste byproducts. We propose to overcome the problems inherent to synthetic pheromone production by designing and developing an innovative green chemistry alternative while minimizing hazards. Our strategy involves the use of a cost-effective plant factory expressing a suite of biosynthetic enzymes for production of moth pheromones.

An excellent summary of this research is provided by Kansas State University.

Smells Like Pine-Sol® ?

Now, on a much larger scale, comes a report that a familiar plant VOC – the scent of pine – may have a role in mitigating climate change.

Published online 26 February, 2014, a report in Nature magazine (see Ref. 3 below) by German, Finnish and U.S. scientists “…elucidates the process by which gas wafting from coniferous trees creates particles that can reflect sunlight or promote cloud formation, both important climate feedbacks.” (From a summary of this research provided by the University of Washington.)

And here’s a bit more from Nature’s Editorial summary:
Forests emit large quantities of volatile organic compounds to the atmosphere. The condensable oxidation products of volatile organic compounds emitted by forests can form secondary organic aerosols or SOAs that can affect the Earth’s radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. But our understanding of the link between biogenic volatile organic compounds and their conversion to aerosol particles remains limited. This study reveals that a direct reaction pathway can lead from volatile organic compounds to low-volatility vapours that can then condense onto aerosol surfaces producing secondary organic aerosol and can significantly enhance the formation and growth of aerosol particles over forested regions.”

Plants…they’re a gas!

References

1. Harren, F. J. M. and S. M. Cristescu (2013) “Online, real-time detection of volatile emissions from plant tissue.”, AoB PLANTS, Vol. 5 : plt003, doi: 10.1093/aobpla/plt003. (Full Text)

2. Ding, B.-J., et al. (2014) “A plant factory for moth pheromone production.” Nature Communications, Vol. 5, Article number: 3353. (Full Text)

3. Ehn, M., et al. (2014) “A large source of low-volatility secondary organic aerosol.” Nature, Vol. 506, pp. 476–479. (Abstract)

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