TRANSFORMATION OF SUGARS IN EXCISED BARLEY SHOOTS

Abstract

Sucrose was synthesized in barley plants when any one of the following monosaccharides was supplied: glucose, fructose, mannose and galactose. This indicates that the plant possesses a mechanism to convert these monosaccharides into glucose or fructose. Maltose and lactose can also be utilized by barley for sucrose formation. The plants, apparently, possess enzymes which are able to hydrolyze these disaccharides to their respective monosaccharides, which are then used for the synthesis of sucrose. Synthesis of sucrose from monosaccharides took place in etiolated plants in the dark. Arabinose, xylose, mannitol, sorbitol and gluconic and pyruvic acids were not utilized by the plant for sucrose formation. When excised barley shoots respired for 24 hrs. the sucrose gradually diminished, apparently due to hydrolysis, but the reducing sugars remained approx. at a constant level throughout that period. Only after the sucrose was entirely depleted could a diminution in the reducing sugars be observed. An excess of reducing sugars induced synthesis of sucrose; an excess of sucrose favored hydrolysis. Synthesis of sucrose did not occur without the presence of O2.