August 15, 2008

Why Chili Peppers Bring a Tear to Your Eye: It's the Fungus

Esto burrito es muy caliente!There are myriad things for which we should be grateful to the kingdom Fungi. Without them, our forests would be brimming with kindling, all of our bread would be crackers, and we'd have no adult beverages with which to drown our sorrows and make us feel witty and attractive when other elements of nature and nurture haven't conspired to truly make us so. Some of them provide the raw material for anti-cancer drugs and antibiotics, and ongoing research shows certain fungi to be promising possibilities to produce biofuels and extract various toxins from the ground.

Now we learn that there's one more thing for which we have to thank even pathogenic fungi. Without them, Mexican and Indian food would be bland. New research supports the hypothesis that chili peppers spice up our lives because they evolved a chemical weapon in order to combat fungi that would otherwise have digested their seeds.

Self-Defense: Why Chili Peppers Pack Heat
By Andrea Thompson

Chilies, like other fruits, use sugars and lipids to attract birds and other hungry animals that will eat them and eventually scatter their seeds in the process.

But fungi and plant-feeding insects, which puncture chilies' outer skin and allow the fungi to invade, can also try to get in on the meal. Working together, they can destroy a fruit's seeds before it gets a chance to reproduce...

Chilies have evolved a pungent solution to this problem: They produce chemicals called capsaicinoids that protect them from fungal attack by dramatically slowing microbial growth. The capsaicinoids also produce the tear-inducing heat associated with the spicy fruit, though this doesn't bother hungry birds.

"Capsaicin doesn't stop the dispersal of seeds because birds don't sense the pain and so they continue to eat peppers, but the fungus that kills pepper seeds is quite sensitive to this chemical," Tewksbury said.

He added that the chilies' spicy defense mechanism is "a great example of the power of natural selection..."

Plants that lived in areas where fungal attacks were common also produced higher levels of capsaicinoids. But plants that lived in less dangerous areas were as mild as a bell pepper, the researchers found...
I know from personal observation that some mammals aren't bothered by capsaicinoids, too. In particular, I know that raccoons have no problem dealing with the compounds that make we humans cry. I've watched them eat Indian food that I couldn't eat myself because of the overwhelming, mouth-searing chili content. This makes some sense; the peppers' seeds can pass through the digestive tract of a mammal for dispersal just as they do through that of a bird.

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