Glucose from leaves and stalk tissue reserves rapidly move to the kernels, especially in days 10 to 40 after pollination. Most is deposited in the special organelles within endosperm cells called amyloplasts. These plastid structures have their own genome, and like chloroplasts in leaf cells, are believed to have been derived by blue-green algae. Amyloplasts are found in other plants tissues such as fruits and potato tubers. They specialize in conversion of glucose, and sucrose, molecules into the more complex and less water-soluble starch molecules.
Synthesis of starch in corn endosperm amyloplasts involves a series of chemical reactions driven by at least three critical enzymes. Several hundred glucose molecules are joined together in branched molecules to form amylopectin. Normal corn endosperm amyloplasts also have enzymes to join glucose molecules in non-branched, more compact molecules called amylose. Amylose, perhaps because of it compactness, is less easily digested into its glucose components than amylopectin. The branching and non-branching aspects of these two starch molecules in corn endosperm affect eventual human uses of corn as food, animal feed and industry. For example, amylose is less soluble in water, making it more useful as a gelling agent in foods.
Most corn endosperm starch is composed of about 70% amylopectin and 30 % amylose. Genetic mutants can dramatic change to ratio into more amylopectin (waxy corn) or more amylose ( high amylose corn).
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About Corn Journal
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.