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Furanocoumarins as potent chemical defenses
Furanocoumarins are toxic compounds found primarily in species of the Apiaceae and Rutacea.  They come in a variety of flavors and have adverse affects on wide variety of organisms, ranging from bacteria to mammals.  Some of the furanocoumarins are photoactive--their toxicity is enhanced in the presence of ultraviolet radiation.   One of the better-studied modes of toxicity involves the binding of furanocoumarins to DNA.  However, furanocoumarins have also been shown to interact with protein and lipids. 
Fcbiosyn.jpg (79865 bytes)Biosynthesis involves contributions from two pathways, the phenylpropanoid pathway and the mevalonic acid pathway. The immediate precursors for furanocoumarin synthesis are umbelliferone and isoprene.  Two categories of furanocoumarins are produced; the linear furano- coumarins have the furan ring in line with the benz-2-pyrone nucleus, while the angular furanocoumarins have the furan ring oriented at an angle to the nucleus.
 

furanocs.jpg (52707 bytes)The furanocoumarins found in wild parsnip are shown at left and play a dominant role in resistance of this plant to its principal enemy the parsnip webworm (see coevolution). 

People, as well as insects, can suffer from exposure to these compounds.   "Celery picker's itch" and "bartender's itch" are two maladies suffered when humans come into contact with furanocoumarin- containing celery plants or the oil of lime peels.  The symptoms are dramatic, as shown from our own personal experiences below:

 
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artderm.JPG (58544 bytes)In the most severe cases, blisters will develop (top).  In less severe cases, the skin will become hyperpigmented and can remain so for several weeks (left, bottom).

 

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last updated 6/14/2010