Corn endosperm emphasis
Interest in the domesticated teosinte after the discovery of the mutants that allowed kernels not to be immediately released from the ‘cob’ and absence of the hard encasement around the kernel was selection for endosperm types. This part of the kernel is where the majority of carbohydrates are stored. The C4 photosynthesis process of teosinte was a major contribution of this ancestor of corn.
The endosperm of the corn kernel is composed of two major cellular structures. The outer layer of the endosperm cells, the aleurone, includes a concentration of proteins activated as enzymes to digest the starch into sugars utilized as energy driving the germination activity of the seed. The aleurone is also the site of synthesis of anthocyanins, often functioning as antitoxins that can ward off pathogens. The bulk of the endosperm are cells storing carbohydrates usually in the form of starch. These inner endosperm cells are also the site of carotene biosynthesis.
Ease of transport and potential food use of this new species thousands of years ago led to multiple selections of genetics coinciding with environments from the Andes to lowland tropics in South America. Corn had spread to much of North America before Europeans arrived 7000 years after the initial domestication of teosinte. Human emphasis on endosperm development included not only larger deposits of starch but also specific characteristics.
Carotene synthesis includes multiple steps but if the recessive mutation of the Y1 gene is present this process isn’t completed resulting in no yellow pigment and white endosperm. Aleurone anthocyanin colors are dependent upon three genes affecting that process. A dominant gene, labeled as C1 allows color to be developed, the recessive c1 form of the gene prevents colored aleurone layer. Another dominant gene R1 also allows a colored aleurone pigment. If dominant gene Pr1 is combined with R1 or C1, a purple or blue color is developed in the aleurone layer of cells. Recessive form of the gene (pr1) results in red corn if the C1 or R1 is present. White corn has the recessive y1 activity in the center part of the endosperm and recessive c1 and r1 in the outer aleurone layers. Yellow corn has the dominant Y1 combined with c1 and r1.
As corn was utilized by ancient and modern corn breeders, other endosperm modifications became emphasized. While the attention remains on endosperm characteristics, selections for the multiple genetics involved in plant development appropriate to the environments also occurred. This has led to the large diversity available to current corn breeders.
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The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.