Chili Peppers Evolved Heat to Kill Fungi

Why are chilies spicy? Scientists from the University of Washington say that spiciness is a defense mechanism that some peppers develop to fight off a seed killing fungus. The spiciness comes from capsaicinoids, chemicals that protect plants from fungal attack by dramatically slowing microbial growth.

Joshua Tewksbury and his colleagues studied a type of chili from Bolivia that comes in different versions, from hot as a jalapeño to mild as a bell pepper. They found out that plants that lived in areas where fungal attacks were common produced higher levels of capsaicinoids. Using chemical substances as a defense is not unique to peppers. Tomatoes, for example, produce phenolics that give their unripened fruit a decidedly unpleasant taste, allowing the seeds a chance to mature and be dispersed. But unlike peppers, tomatoes and most other fruits lose their chemical defenses when the fruit ripens. Tewksbury said that in contrast, peppers increase their chemical defense levels, or their heat, as they ripen and they can get away with it because birds don't sense pain when they eat capsaicin.

So the next time you nibble on spicy jalapeño poppers, remember that you’re sampling one of the earliest examples of chemical warfare.

For more information, read http://www.uwnews.org/ The paper published by PNAS is available at http://www.pnas.org/content/early/2008/08/08/0802691105.abstract