Secret about heat in chilli peppers
If you’re a fan of Asian cuisine or like to order spicy indian food you owe a lot to bugs, both the crawling kind and ones you can see only with a microscope. New research shows they are the ones responsible for the heat in chili peppers.
The spiciness is a defence mechanism that some peppers develop to suppress a microbial fungus that invades through punctures made in the outer skin by insects. The fungus, from a large genus called Fusarium, destroys the plant’s seeds before they can be eaten by birds and widely distributed. However, the researchers found that the pungency, or heat, in hot chilies acts as a unique defense mechanism. The pungency comes from capsaicinoids, the same chemicals that protect them from fungal attack by dramatically slowing microbial growth.Capsicum chacoense is naturally polymorphic for the production of capsaicinoids and displays geographic variation in the proportion of individual plants in a population that produce capsaicinoids.
Caption: Two hemipteran bugs attack the ripened fruit of a chili plant, and scars from previous attacks are visible. Such attacks leave the fruit open to a fungal infestation that can kill the plant’s seeds.
Credit: University of Washington
“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,” said Tewksbury, lead author of a paper documenting the research.
“Having such a specific defense, one that doesn’t harm reproduction or dispersal, is what makes chemistry so valuable to the plant, and I think it is a great example of the power of natural selection.”
The fact that chilies have capsaicin could be the reason humans started eating the peppers in the first place, he said. Chili peppers and corn are among the earliest domesticated crops in the New World.
Reference:
Oshua J. Tewksbury, Karen M. Reagan,Noelle J. Machnicki,Tomás A. Carlo,David C. Haak,Alejandra Lorena Calderón Peñaloza,and Douglas J. Levey.
Evolutionary ecology of pungency in wild chilies
PNAS published August 11, 2008, doi:10.1073/pnas.0802691105
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