26 April 2013

Plants Fluoresce for Bugs

Welcome back. I haven’t written about plants--vegetation--since my Lawn and Garden post two years ago. That post received so many rave reviews, I thought I could just rest on my laurels (get it?). But a recent research report has me going botanical again.

The article that tipped me off to the report confused the heck out of me. Fortunately, Cornell Professor William Philpot was available for consultation. We decided the article got enough of it wrong that I’ll forgo listing that article in my P.S.

Before highlighting the research finding, which will tempt you to rush out and buy a to-be-identified plant if you don’t already have one, I’ll start with some not so new but definitely interesting plant facts.

Bugs See the Light

You probably know that plants go shamelessly out of their way, proffering nectar, aroma and color, to attract bugs that might help the plants pollinate. “Color” is the light a plant reflects--green, red, blue. Although you and I get tan, ok, sunburned from ultraviolet light, which I’ll write as “UV,” we can’t see the UV reflected from a plant. But most bugs can.

In fact (here’s the cool part), some plants reflect UV in such a way that the plant looks like a target. The pattern of reflected UV light becomes a nectar guide with a bright outer area surrounding a dark center.
Yellow sorrel reflecting visible (top) and UV light.
(from http://www.sciencedirect.com/science/article/pii/S0030399208002442)

Plant Fluorescence

There’s more. Some plants try harder, though they’re more interested in attracting prey than pollinators. Certain carnivorous plants not only reflect light, they also emit light.

If you’ve gotten this far, the rest will make a lot more sense if you understand that light and color can be described by wavelength. Wavelengths that humans can normally see range from blue, at the short end, through green, up through red at the long end. UV wavelengths are a bit shorter than blue wavelengths, beyond the range of human vision.

Researchers at the Jawaharlal Nehru Tropical Botanic Garden and Research Institute in India found that when selected carnivorous plants were stimulated or excited with a specific wavelength of UV light--light that would be delivered by sunlight--some of the plants exhibited fluorescence. Those plants emitted light at that same UV wavelength as well as at a blue wavelength.

A Blue Glow

Venus flytrap in action. (multiple websites)
Common carnivorous plant traps for catching bugs and small critters include pitfall traps, which have tall rolled leaves that hold pools of digestive liquid (e.g., pitcher plant), snap traps with quick-closing leaves (e.g., Venus flytrap), flypaper traps with sticky stuff (e.g., butterwort), and bladder traps (e.g., bladderworts), which suck in the prey. Plants of each type were tested.

Two of the four types, the pitfall trap and snap trap plants, exhibited the UV and blue fluorescence. When scanned at the UV wavelength, a distinct blue fluorescence appeared on the lids, inner tubes and rims of pitcher plants, and the inner sides of Venus flytraps glowed blue.

To gauge the importance of the fluorescence for attracting prey, the investigators masked the blue emission of pitcher plants and monitored how well they attracted prey over 10 days. The capture success was sharply reduced, suggesting that blue fluorescence ranks up there with nectar, aroma and reflected colors.

Wrap Up

If you’d like to peek at the UV light reflecting from plants or for that matter from anything, you’ll need a special viewer.

To view the blue fluorescence--if the research findings are correct--you’ll need a pitcher plant or Venus flytrap (and bugs). I’m not sure how easy it will be to see. You should be able to boost the fluorescence with a UV lamp (black light) and low-light conditions. Let me know if it works. And thanks for stopping by.


- Research paper in the journal, Plant Biology: http://onlinelibrary.wiley.com/doi/10.1111/j.1438-8677.2012.00709.x/abstract
- Good summary article: http://www.bbc.co.uk/nature/21459520
- Nice summary of nectar guides: http://www.cals.ncsu.edu/course/ent591k/nectar_guide.html
- Wikipedia article on carnivorous plants: http://en.wikipedia.org/wiki/Carnivorous_plant
- Link to International Carnivorous Plant Society: http://www.carnivorousplants.org/

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