Cereal Chem 51:798 - 808.  |  VIEW ARTICLE
In Vivo Incorporation of Carbon-14 into Zea mays L. Starch Granules.

J. C. Shannon. Copyright 1974 by the American Association of Cereal Chemists, Inc. 

A positive linear relationship existed between starch granule size and radioactive starch per granule at 29 and 50 hr. after exposure of Zea mays L. plants to 14CO2. This relationship was observed in starch granules isolated from kernels 14 to 41 days post-pollination. The 14C per unit surface area was similar for granules in the five larger size classes, but the smallest granule class contained only half as much 14C per unit area of granule surface. Based on these data it is suggested that the smallest granules are derived from physiologically younger cells. Starch synthesis in such cells may rely on synthesis from UDP-glucose by the less efficient granule-bound UDP-glucose-starch glucosyltransferase rather than being able to utilize ADP- glucose and/or glucose-1-P as substrates. Cells containing starch granules having an average of at least 0.12 gamma of starch per granule are probably synthesized from ADP-glucose or glucose-1-phosphate via the action of granule-bound and soluble nucleoside diphosphate-glucose-starch glucosyltransferase and phosphorylases II and III, respectively. However, since the 14C per unit surface was similar for the five largest granule size classes, the rate of starch synthesis in these granules was probably regulated by the surface area available for starch deposition.