Starch is the major storage carbohydrate of higher plants. In wild-type maize, starch consists of 25% amylose and 75% amylopectin. Starch and its chemically modified derivatives are of great importance to the world's food supply and economy. Starch-based products have long been used as sources for sweeteners and numerous other food and industrial ingredients, including pharmaceuticals, fat substitutes, textiles, packaging materials, and adhesives. The increasing agricultural and industrial importance of starch and its derivatives has raised interest in the possibility of producing bioengineered starches with improved functional properties.

Bioengineering of the genes encoding the major starch biosynthetic enzymes has the potential to modify starch yield and starch structure. In theory, gene alteration can be used to modify structural features such as the ratio of amylose to amylopectin, chain length and polymer size, degree of branching, the spacing between branch points, and the subsequent attachment of phosphate or sulfate groups. A detailed understanding of the enzymes that function within the starch biosyn-thetic pathway in higher plants is therefore vital.

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