|MadSci Network: Botany|
In addition to attracting people with their beautiful colors and fragrant aromas, flowers also attract insects, usually for the purpose of moving pollen from one flower to another. This is a finely tuned system with a combination of smells and colors (including some we can't even see) to attract a specific insect to visit the same species of flower. The effort of producing pollen is wasted if it doesn't get to the stigma of the same species. During the course of evolution, it was advantageous to those flowers which produced an attractant. The attractant production was an accident but had the effect of increasing pollination for the species. What kinds of molecules are the attractants? Each fragrance is a combination of a number of chemicals, but most of them are from a large and diverse family of molecules known as terpenes. Chemically, terpenes are composed of different numbers and types of 5-carbon chains. All plants make some terpenoid compounds, specifically chlorophyll and the carotenoids needed for photosynthesis. You are probably more familiar with them from your interaction with some of the volatile terpenes (these are ones you can smell) which are major components in the aromas of lemon, camphor, menthol, mint, and turpentine. As you might guess from this list, terpenes can act as repellants as well as attractants, which can also be useful to the plant. The plants did not set out to make all of these fragrant molecules. They are what are called "secondary products" which means that they have no known use in the basic metabolism of the plant. They were probably intermediates in the synthesis of a larger terpene (such as chlorophyll) which were accumulated due to a mutation. Sometimes these mutations had an advantage for the plant by attracting pollinators or repelling predators. Plants which had the mutation were able to produce more seeds, which also had the mutation. Thus, the change was passed on to the next generation. You can read about some of the recent research in Anthurium in the journal Phytochemistry vol. 49, p. 521-528 (some of this work was done at the Missouri Botanical Gardens, just a short ride from Mad Scientist headquarters) or some work on orchids in the journal Science vol.164, p. 1243-1249. Go to the site http://www.gi.alaska.edu/ScienceForum/ASF8/852.html for a short discussion of some terpenes or search the web under "terpenes" to find the many ways terpenes touch (literally) your everyday life.
Try the links in the MadSci Library for more information on Botany.