Bitter-tasting nectar and floral odors optimize outcrossing ...(o understand the floral biochemistry and...)

Date:8/28/2008

o understand the floral biochemistry and plants' ecological interactions with their mobile visitors, the researchers generated four different lines of genetically modified wild tobacco (Nicotiana attenuata). Apart from control plants that had received only a blind copy of the transgenic DNA fragment, transgenic lines were created (by means of RNA interference) that were unable to produce either nicotine or benzyl acetone; the latter has a sweet odor we know from cocoa beans and is similar to the smell of jasmine and strawberry. A fourth line of transgenic plants could produce neither nicotine nor benzyl acetone.

After a series of control experiments in the field showed that the genetic modifications per se did not influence growth, flower formation, nectar production, or the frequency of outcrossing, the scientists ran a series of three tests: First, measurements of floral nectar showed that its volume was only half the size in transgenic plants which were impaired in nicotine production, compared to control plants and the lines that could not produce benzyl acetone as an attractant. Conclusion: Floral visitors are principally attracted by the scent, and they drink more nectar if it doesn't taste bitter. Using video cameras, the researchers confirmed this result: Both attractant-deficient lines were rarely visited by hummingbirds (e.g. Archilochus alexandri) and white-lined sphinx moths (Hyles lineata). When visitors took nectar from flowers which contained a natural amount of deterring nicotine, they stayed for a short time only, while they enjoyed the nicotine-free nectar of corresponding transgenic lines. Consequently, these flowers were visited for longer periods, especially by hummingbirds.

However, such observations do not prove that different visiting behaviors affect outcrossing and reproduction among plants. Therefore, two further analyses were performed, one focused on female fitness (production rate of seeds in the
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Contact: Ian T. Baldwin baldwin@ice.mpg.de 49-175-180-4226 Max Planck Institute for Chemical Ecology Source:Eurekalert

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