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辣椒产辣是为了预防菌类的侵袭
Main Category: Nutrition / Diet
Article Date: 12 Aug 2008 - 3:00 PDT
Despite the popularity of spicy cuisine among Homo sapiens, the hotness in chili peppers has always been something of an evolutionary mystery.
A plant creates fruit in order to entice animals to eat and disperse its seeds, so it doesn't make sense for that fruit to be painfully hot, said University of Florida zoology professor and evolutionary ecologist Douglas Levey.
But according to new research by Levey and six colleagues from other universities, chilies have a very good reason to make themselves hot. It boils down to protection.
Based on research on wild chili plants in rural Bolivia, the scientists found that the leading cause of seed mortality is a fungus called Fusarium. The fungus invades the fruits through wounds made by insects and destroys the seeds before they can be eaten and dispersed.
Capsaicin, the chemical that makes the peppers hot, drastically slows microbial growth and protects the fruit from Fusarium. And while capsaicin deters local mammals, such as foxes and raccoons, from consuming the chilies, birds don't have the physiological machinery to detect the spicy chemical and continue to eat the peppers and disperse seeds, Levey said.
The researchers' findings will be released in a paper published online by the Proceedings of the National Academy of Sciences.
Levey and his colleagues were able to arrive at these conclusions because at least three of the approximately 15 species of chilies that grow in the Bolivian wild are polymorphic for pungency, which means that some individuals of those species produce pungent fruit and others produce non-pungent fruit. This provided the researchers with natural experimental conditions under which they could compare Fusarium attack on fruits with and without capsaicin.
Upon studying various chili pepper plants, the researchers observed a clear correlation between high levels of capsaicin and low seed mortality due to fungal growth, Levey said.
And the chemical doesn't just help the plants that produce it, either. Levey said the consumption of chilies can help protect humans from the dangerous diseases that are so plentiful in tropical climates.
"The use of chili peppers as a spice has spread to nearly every culture within 20 degrees of the equator, and it tends to decline as you move toward the poles," Levey said.
The capsaicin in chilies, one of the first plants domesticated in the New World, may have been used to protect human food from microbial attack long before refrigeration or artificial preservatives were available, he said.
One question Levey and his colleagues are still pondering is why any nonhot chilies remain if capsaicin is so beneficial. Their hypothesis is that the production of the chemical comes at a steep price for chili plants.
Levey said the plants that produced hot chilies had seeds with very thin coats - a presumed consequence of sacrificing the production of lignin, a complex molecule that makes up the protective seed coat, in favor of the production of capsaicin.
This phenomenon represents an interesting tradeoff between chemical and physical seed protection and demonstrates the power of natural selection, Levey said.
At higher elevations, where moisture is high and Fusarium fungus is rampant, the scientists found that 100 percent of the plants produced hot chilies. In the drier lowlands, where fungus is less of a problem, only 40 percent of the plants produced fiery fruits. The remainder spent more resources developing thick seed coats, which protect against the devastating ant populations common to lower areas.
While all of the plants look identical, telling the difference between hot and non-hot chilies is not difficult, Levey said.
"Just pop one in your mouth," he said. "You'll find out pretty quick."
The lead author of the paper is Joshua Tewksbury, of the University of Washington. In addition to Levey, co-authors are Karen Reagan, Noelle Machnicki, Tomás Carlo, and David Haak of the University of Washington; and Alejandra Lorena Calderón Peñaloza of Universidad Autonoma Gabriel Rene Moreno in Bolivia. The work was funded by the National Science Foundation and the National Geographic Society.
University of Florida
http://www.medicalnewstoday.com/articles/117948.php 本人已认领该文编译，48小时后若未提交译文，请其他战友自由认领 新的研究揭示为什么辣椒是辣的
Main Category: Nutrition / Diet
Article Date: 2008年8月12日- 3:00 PDT
尽管辣的菜在现代人中很流行，但是红辣椒的辣一直是神秘发展的。佛罗里达大学动物学教授和进化生态学教授Douglas Levey说，一种植物结出果实是为了引诱动物来吃并传播它的种子，因此如果果实太辣是没有意义的。但是按照Levey和来自其他大学的六个同事的最新研究结果，红辣椒的辣是有一个非常好的原因的。 它是为了保护自己。基于对玻利维亚郊区野生辣椒的研究，科学家发现导致植物死亡的主要原因是一种名为镰刀霉的菌类。 这种菌类通过昆虫咬伤的部位侵袭果实，并且在他们被吃掉和散播之前把种子毁坏。辣椒碱-使辣椒变辣的化学物质-能显著减缓微生物生长和保护果实免受菌类侵袭。Levey说：当辣椒碱阻止当地的动物（例如狐狸和浣熊）吃红辣椒时，鸟类没有发现辛辣的化学物质的生理机能，他们继续吃辣椒并且传播种子。研究者们的研究结果将以论文的形式在线发表在国家科学研究院学报。Levey和他的同事能够得到这些结论，是因为生长在玻利维亚野外的大概15种辣椒中的至少3种具有不同的刺激性，这意味着这些种类中的某些个体结出辛辣的果实，而其他结出不辣的果实 这给研究者提供了天然的研究条件，在这种条件下他们可以比较镰刀霉对含有和不含辣椒碱果实的侵袭情况。Levey说，在研究了各种辣椒品种后，研究者发现了由于真菌生长，在高辣椒碱水平和低死亡率之间明显的关联。
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作者:admin@医学,生命科学 2011-02-13 05:14
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