Sex.
Animals do it.
And plants do it, too.
To enhance sex (cross-pollination), the flowers of some plants not only produce chemical pigments (colors) and sugary nectar to attract pollinators, but also volatile chemicals (scents) to do the same. In addition to these chemical attractants, flowers may also produce chemical repellents, such as nicotine (see below) to inhibit non-pollinating insects or animals from eating the flower or stealing floral nectar.
Scientists have recently discovered that flowers producing both a volatile chemical attractant and repellent may actually enhance the reproductive success the desert tobacco (Nicotiana attenuata) that grows in the American southwest.
As reported in the 29 August 2008 issue of Science Magazine, Danny Kessler, Klaus Gase and Ian T. Baldwin (Max-Planck-Institute for Chemical Ecology, Jena, Germany) have provided evidence that by producing a combination of attractants and repellents flowers may reduce predation and promote outcrossing. They did this by employing a rather unique approach of using genetically-transformed plants for field ecological studies.
By blocking pertinent biosynthetic genes in the transformed plants, they were able to manipulate the levels of attractant (benzyl acetone, BA) and repellent (nicotine, N) in native tobacco plants and to produce an array of plants with different attractant/repellent combinations. The relative reproductive success of these plants was then measured in native habitats.
Bottom line: native tobacco plants that produced a combination of BA and N did best. The authors hypothesize that the presence of N both repelled predators and reduced the amount of time pollinators lingered at each flower. Pollinators then visited more flowers, thus promoting the frequency of outcrossing.
Flower components nicotine (N), a repellent present in the nectar, and benzyl acetone (BA), a volatile attractant released by petals (right). Both components optimize the plant’s production of outcrossed seeds.
Danny Kessler, MPI Chemical Ecology
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