#PlantPorn, #PlantsMakePeopleHappy, Plant History

Do You know Your Corn?

November 17, 2017

Corn (Zea mays) has been a staple crop of the Americas for the past 6,500 years or so.  In fact, since its domestication from the wild teosinte, corn has been extensively bred for different purposes and three general categories of corn exist: corn for popping, corn for mash (and fodder), and sweet corn for eating.  Let’s explore a little bit about corn before getting to the glass gems bit.

Corn Field NJ Christopher Satch

A field of corn in Sussex County, NJ – Christopher Satch

Three Ways We Consume Corn

Not all corn can be popped!  Popcorn kernels have the ability to pop due to the moisture inside each kernel (and have been bred to contain more moisture than other corn).  As the kernels are heated, the water vaporizes and steam cooks the starch. The steam creates pressure in the kernel, and when the pressure becomes too great the steam bursts out of the kernel allowing the starch to expand at such a rate that the entire kernel is turned inside-out!

Corn for mash is often ground up for either animal fodder or corn flour.  This is the stuff tortillas are made of.  This corn cannot be eaten raw or cooked, as the kernels are extremely hard, and will definitely shatter your teeth!  Mash corn is also ground up and fermented, then distilled to make bourbon whiskey (other whiskeys use barley or rye).  Lower grade mash corn, or corn that is unfit for human consumption, is often used in animal fodders and feed.

Sweet corn is the good stuff—higher in sugars than starches this corn is soft when boiled, and is a staple of sizzling summers all across the Americas.  Its softness can be partially attributed to the physical properties of starches versus sugars.  When boiled, the sugars solubilize within the kernel, changing from solid to liquid, and thus softening the corn.  Starch is much less soluble, and when packed becomes much denser and harder than sugars.

transposon corn mcclintock

Variegation caused by transposon activity in corn – © 2002 Nature Publishing Group Feschotte, C. et al. Plant transposable elements: where genetics meets genomics. Nature Reviews Genetics 3, 330.

The Genetic History of Corn

So, now that you’re hungry, let’s talk genes.  Corn is currently the focus of much gene research and otherwise for its importance as a grain.  The entire genome of corn was discovered and sequenced in 2009.  You can read about that team here.  However, corn’s use in genetics goes back even further.

Dr. Barbara McClintock was one of the first few women to earn her PhD from Cornell in Botany in 1927.  Her research focused on maize cytology (cytology is the study of the cell) where she studied the chromosomes of corn cells.  By staining the cells of corn kernels, she was able to see the chromosomes clearly, and the patterns and bands on each one.  By working with an inbred line of corn (inbred lines have uniform genetic makeup), she was able to see correlations with changes in the bands of the chromosomes and phenotype (physical appearance) of the kernels.

More variegation caused by transposons in corn – Carolina Scientific

This was the physical proof for the ‘crossing over’ of genetics, even though the mechanism at that time was still unknown.  This crossing over, she theorized at the time, was due to transposable elements, or transposons – DNA that ‘copies and pastes’ into other chromosomes/locations or ‘cuts and pastes’ into other chromosomes/locations.  Transposons containing color pigment genes were proven to produce mosaic patterns on corn kernels and variegation in the leaves of the corn.  During cell division (mitosis) some cells would randomly receive pigment genes.  This explains why the mosaic patterns were never repeated in any other corn or corn progeny.

Her work would be largely ignored for another 30 years until the technology caught up with her theories in the Genetic Revolution of the 1960’s and 1970’s and other scientists were able to support her theories.  In 1983, she was the first woman to outright win the (unshared) Nobel Prize in Physiology or Medicine for her work in the 1930’s for her discovery of transposons.

Glass gems corn can be understood with transposon, and other genetic principles that McClintock and other geneticists have discovered.  Like many species of domesticated plants, a wild population where the crop was first domesticated usually exists.  For example, corn was domesticated from wild corn in Central America.  We call this the center of origin for the corn.  At the center of origin, genetic diversity is the greatest, as wild populations still exist.

As corn was bred and its cultivation spread throughout the Americas, different native tribes were cultivating different types of corn.  It wasn’t until the 1930’s and on that huge monocultures of specially-bred hybrid corn were being planted that corn diversity decreased—heirloom varieties were not being grown because they were not as productive as the hybrid corn.

Although we did lose a lot of genetic diversity, there has been a revival since the 2010s to plant heirloom varieties.  Why plant them if they’re not as productive?  It’s because they have a wealth of random genes for different traits that we could use for plant breeding.  Certain heirloom lines of corn may have resistance to disease, or produce more nutritional corn, even if the size or other attributes are less desirable.

‘Glass Gem’ corn – Greg Schoen

Carl Barnes, a half-Cherokee midwesterner, started to plant heirloom varieties of corn in order to connect with his Cherokee roots.  He had exchanged seeds from collectives from all over the country, and had begun to select for the most colorful corn that popped up.  Over time, these native varieties had crossed with one another (as they do!) to form the Glass Gems hybrid that went viral over the internet in 2012.  The Native Seeds/SEARCH website still sells the popular seeds.

-Greg Schoen

Luckily enough, this corn can be grown successfully in large containers outdoors that’ll be sure to make you the talk of the town… or at least the talk of Thanksgiving dinner!

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