The nectar of plants may be more than just nourishment for the birds and bees that feed off of them - instead, suggests a study published in this week's issue of Science, it may be a complex chemical cocktail that simultaneously attracts and repels pollinators in order to optimize the amount of time they spend at each flower and the attention they pay to flowers on different plants.

"This paper shows just how sophisticated a plant can be in using chemistry to get what it wants, which is to outcross," said Ian Baldwin from the Max Planck Institute for Chemical Ecology in Germany, the study's lead author.

Baldwin and his colleagues studied a species of tobacco named Nicotiana attenuata, which synthesizes benzyl acetone to attract the hummingbirds and hawk moths that spread its pollen and sup on its nectar. That nectar also contains nicotine, which ensures that these pollinators don't spend too much time at one flower or at one plant; a good thing for a plant that wants its gametes spread far and wide to maximize the genetic diversity of its offspring, said Baldwin.

Using molecular tools such as RNA interference, the researchers silenced the genes that express benzyl acetone and/or nicotine in different combinations, and then observed the effects of the changes on the behavior of pollinators.

The research team found that pollinators visited plants lacking benzyl acetone less than plants that made benzyl acetone. Conversely, pollinators tended to loiter at flowers that made benzyl acetone but lacked nicotine, indicating that the presence of nicotine in the nectar encouraged modest drinking behavior. The findings suggest that nectar is not merely a sugary reward for pollinators and is instead a more subtly concocted brew. "[These results] turn the tables on the notion that nectar is just a fitness drink," said Baldwin.

Their focus on the role chemical attractants and their combined use of advanced genetic techniques and traditional behavioral experiments is novel in the world of pollination biology research. "[Baldwin and his coauthors] used a very elegant and precise method to manipulate the flowers," said Robert Raguso, a Cornell University chemical ecologist who was not involved with the study. "Most people who study pollination don't think about chemistry."

Baldwin and his coauthors also tracked the reproductive success of the transgenic plants with modified nectar compositions. They found that having just the right combination of benzyl acetone and nicotine maximized an emasculated flower's ability to produce healthy seed capsules by encouraging more frequent visits from pollinators. This is especially interesting in light of the fact that Nicotiana attenuata is a self-pollinator, and does not actually require outside gametes from other plants to successfully reproduce. Getting pollinators to flit from flower to flower and plant to plant seems to ensure that pollen from a wider diversity of individuals makes it into the mix. "The plant is clearly manipulating its visitors in a way that optimizes its success," explains Raguso, who wrote an accompanying Perspectives piece in the same Science issue. "They're topping off seed production with a few outcrossed seeds. They're gamblers. For them this is kind of a bet hedge."

So will this paper revolutionize the way that botanists think about the techniques plants use to attract pollinators? Perhaps, but at the very least it sheds light on aspects of the plant-pollinator relationship that have been overlooked in the past. "It brings to the forefront what really had been sideline players in the floral drama," Raguso said.