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Movement and Metabolism of Sucrose in Developing Barley Kernels¹

Sucrose metabolism in developing barley (Hordeum vulgare L.) kernels was studied from anthesis to physiological maturity. To follow the fate of sucrose entering the developing barley kernel, ¹⁴C-sucrose was introduced to specific kernels through the awn of the subtending lemma. After 2 h, kernels were removed and dissected into vascular tissue, outer pericarp, inner pericarp, and endosperm. Leachable sugars were extracted by incubating the tissues in an osmoticum for 1 h at 0 to 1°C. The tissue was transferred to 80% (v/v) ethanol to extract nonleachable sugars. Starch was determined in the residual tissue. Simple sugars in the teachable and nonleachable fractions were separated by paper chromatography. Radioactivity in all fractions and incorporated into starch was determined. Throughout kernel development, the tissue containing the largest percentage of ¹⁴C fed to the kernel from the subtending awn was the endosperm. The pericarps contained a pool of ¹⁴C-sucrose which was easily leached from the tissue. The specific activity of this pool was similar to the specific activity of the teachable pool of ¹⁴C-sucrose of the endosperm. Incorporation of ¹⁴C-sucrose into starch during the 2-h period of the experiment declined with kernel age. These data support the hypothesis that the rate and duration of starch synthesis in barley endosperm are limited by processes within the endosperm, possibly the conversion of sucrose to starch, and not by availability of sucrose to the endosperm.

Key Words: Hordeum vulgare L. • Kernel growth • Starch synthesis

² Former graduate research assistant, now plant physiologist, USDA Metabolism and Radiation Res. Lab., Fargo, ND 58105, and assistant professor, Dep. of Agronomy and Soils, Washington State Univ., Pullman, WA 99164.

Received for publication April 11, 1983.