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United States Department of Agriculture

Agricultural Research Service

Title: CARBON ISOTOPE RATIOS OF AMYLOSE, AMYLOPECTIN AND MUTANT STARCHES

Authors
item Scott, Marvin
item Jane, Jay - IOWA STATE UNIVERSITY
item Soundararajan, Madhavan - UNIVERSITY OF NEBRASKA

Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 18, 1999
Publication Date: N/A

Interpretive Summary: Corn stores energy in kernels in the form of starch. Starch is used for many things including food, films, adhesives and thickeners. Molecules called enzymes work together to make starch. Since there are many enzymes in the seed, it is difficult to determine exactly what each enzyme is doing in starch production. We have found that each enzyme involved in starch production leaves a "fingerprint" called a carbon isotope ratio on the starch it makes. By analyzing these fingerprints, we will be able to learn the roles of specific enzymes in starch production. Understanding the role of each enzyme will allow us to manipulate starch production so that we can breed corn that contains starch suited to a given uses. This will result in more efficient use of starch, which will in turn reduce the cost of starch-containing products.

Technical Abstract: In higher plants, the dry matter ratio of **13C to **12C (typically expressed as a delta**13C value) results primarily from carbon isotope discrimination during C02 fixation, in the carboxylation of phosphoenolpyruvate (C-4 plants) or ribulose-1,5-bisphosphate (C-3 plants). There have been few reports of variation derived from secondary non- carboxylation discriminations in a biochemical pathway. We have applied carbon isotope ratio analysis to the starch fractions amylose and amylopectin and found them to have different delta**13C values. Because amylose and amylopectin are derived from the same pool of Glucose-l- Phosphate, we conclude that enzymes in the biosynthetic pathway of starch contribute measurable carbon isotope discriminations. To test this hypothesis, we analyzed starch isolated from the maize mutants wx and ae which are known to have genetic lesions in the starch biosynthetic pathway. .The delta**13C values of starch from these mutants were significantly different, supporting our hypothesis that enzymes in the starch biosynthetic pathway contribute measurable carbon isotope discriminations to starch.

Last Modified: 7/31/2014
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