February 15 2012

the peculiar case of the puny pepper

Have you ever cut open a bell pepper only to find a strange little surprise waiting for you inside? The first time this happened to me, it seriously freaked me out. I mean, just look at it! What on earth could that possibly be?! A pepper baby? A parasitic twin? An alien pod?


It turns out that these strange peppery growths aren’t that uncommon. Inside Insides caught a glimpse of one in an MRI scan. And botanists have been noticing and writing about them for a really long time. Check out this snippet from the 1891 Bulletin of the Torrey Botanical Club:


If you know any French, you can also check out the 1904 Revue Scientifique du Limosin. And here’s a lovely diagram from the 1906 Missouri Botanical Garden Seventeenth Annual Report. Look familiar?


So what’s going on?

During normal pepper development, seeds develop from fertilized structures known as ovules. Peppers have many ovules, which turn into lots of tiny, obnoxious seeds. Occasionally, a pepper ovule will go rogue and start developing into a so-called “internal proliferation” or “carpelloid structure” that looks much more like a tiny pepper than a seed.

Interestingly, there is a correlation between these internal proliferations and parthenocarpy in peppers. Partheno-what now? Parthenocarpy. It’s the ability of a fruit to form in the absence of fertilization. Normally, fruit only forms if ovules have been fertilized and are properly developing into seeds. If parthenocarpy kicks in, a fruit can form without any seeds at all. What do alien pepper babies have to do with parthenocarpy? A recent paper suggests a model:

Abnormal ovules may convert into carpelloid structures; however, growth of carpelloid structures only becomes prominent in the absence of fertilization/seed initiation, as developing seeds suppress the growth of carpelloid structures. The carpelloid structures mimic the role of seeds and support parthenocarpic fruit growth.
Tiwari et al. (2011) BMC Plant Biology

Understanding what gives rise to these strange baby peppers could actually help us figure out how to make seedless (parthenocarpic) pepper varieties. You can already thank parthenocarpy for the lack of big, nasty seeds in bananas and several types of oranges. Maybe seedless peppers will be next!


Biologist by day, culinary enthusiast by night. What better way to combine my interests in science and cooking than to write about them here?

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