Figure 28.5 Nicotine Is a Defense against Herbivores
In 2004, Steppuhn, Baldwin, and colleagues at the Max Planck Institute for Chemical Ecology in Jena, Germany, tested the hypothesis that nicotine helps protect tobacco plants against insects. The researchers generated a line of low-nicotine transgenic plants by modifying the gene putrescine N-methyl transferase (pmt), which encodes a key regulatory enzyme in the nicotine biosynthesis pathway. Both the low-nicotine and wild-type tobacco plants were transplanted into a field plantation where they were accessible to naturally occurring herbivores. The extent of leaf damage by insects was then measured at two-day intervals for a period of 16 days. Results showed that the low-nicotine plants lost more than twice as much of their total leaf area as the wild-type controls. These results suggest that nicotine provides tobacco plants with at least some protection against insects. To determine if tobacco plants produce other chemical defense compounds, Baldwin and Kessler placed laboratory-raised hungry caterpillars on a group of wild-type tobacco plants. Over the next several days, the investigators used a gas chromatograph to detect the emission of volatile compounds from the damaged leaves. As a control, they also tested nearby undamaged control plants. Baldwin and Kessler then isolated and identified some of these chemical compounds. A few of these chemicals were applied separately to the stems of plants that had not been attacked. Caterpillar eggs were then glued onto the leaves of the treated plants and were monitored for predators that like to eat the eggs. The researchers found that several of the chemicals emitted by the tobacco plants attracted particular insects, including the predator Geocoris pallens. This result suggests that herbivore damage induces the tobacco plants to emit volatile chemicals in order to attract natural enemies of the herbivores. In this manner, the researchers concluded, the tobacco plants can reduce the overall number of herbivores feeding on the plants.
Original Papers
Steppuhn, A., K. Gase, B. Krock, R. Halitschke, and I. T. Baldwin. 2004. Nicotine’s Defensive Function in Nature. Public Library of Science: Biology 2(8): e217.
http://dx.doi.org/10.1371/journal.pbio.0020217
See also the article synopsis:
2004. Nicotine Keeps Leaf-Loving Herbivores at Bay. Public Library of Science: Biology 2(8): e250.
http://dx.doi.org/doi:10.1371/journal.pbio.0020250
Kessler, A., and I. T. Baldwin. 2001. Defensive Function of Herbivore-Induced Plant Volatile Emissions in Nature. Science 291: 2141–2144.
http://dx.doi.org/10.1126/science.291.5511.2141
See also the associated perspectives:
Sabelis, M. W., A. Janssen, and M. R. Kant. 2001. The Enemy of My Enemy Is My Ally. Science 291: 2104
http://dx.doi.org/10.1126/science.1059939
Links
Max Planck Institute for Chemical Ecology: Prof. I. T. Baldwin
http://www.ice.mpg.de/ext/hopa.html?pers=iaba2016&pg=publ&li=ice
Cornell University: Kessler Lab: Research
http://www.eeb.cornell.edu/kessler/html/research.htm
Wikipedia: Plant defense against herbivory
http://en.wikipedia.org/wiki/Plant_defense_against_herbivory
Purdue University: Department of Entomology: Tobacco as Insecticide: A Classroom Activity
http://www.entm.purdue.edu/entomology/outreach/insectivity/tobacco.activity.htm
Plant Physiology 4th ed.: Chapter 13: Essay 13.2: Unraveling the Function of Secondary Metabolites
http://4e.plantphys.net/article.php?ch=13&id=313&search=Unraveling the Function of Secondary Metabolites
Discover Magazine: Talking Plants
http://discovermagazine.com/2002/apr/featplants/?searchterm=Talking%20Plants
Allmann, S. and I. T. Baldwin. 2010. Insects Betray Themselves in Nature to Predators by Rapid Isomerization of Green Leaf Volatiles. Science 329: 1075–1078.
http://dx.doi.org/10.1126/science.1191634