R. L. Whistler and J. R. Young. Copyright 1960 by the American Association of Cereal Chemists, Inc.
Wheat plants were either injected with randomly labeled sucrose-C14 or allowed to take up radioactive carbon dioxide in the light. In both groups of plants, the amylose became labeled much sooner than the amylopectin, clearly indicating that the path to amylose is more direct than the path to amylopectin. Although no evidence is available to suggest that amylose is not converted to amylopectin while these polysaccharides are being formed, the data suggest that amylose is not extensively converted to amylopectin once it has become incorporated into the granule. In plants injected during daylight, radioactivity could be detected in the starch within 4 hours. Those injected during hours of darkness produced little or no labeled starch in 4 hours. Since no activity was found after 4 hours in the heads of plants injected at 11 p.m., translocation of carbohydrates to the head must have stopped during this period of the night. Wheat plants which were grown under different day lengths had starch with the normal 25% amylose content. This indicates that the relative rate of formation of amylose to amylopectin remains the same whether the plant is in light or darkness.