Sucrose Translocation and Storage in the Sugar Beet

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Abstract
Several physiological processes were studied during sugar beet [Beta vulgaris] root development to determine the cellular events that are temporally correlated with sucrose storage. The prestorage stage was characterized by a marked increase in root fresh weight and a low sucrose to glucose ratio. Carbon derived from 14C-sucrose accumulation was partitioned into protein and structural carbohydate fractions and their amino acid, organic acid and hexose precursors. The immature root contained high soluble acid invertase activity (Vmax 20 Mmol/h per mg protein; Km 2-3 mM) which disappeared prior to sucrose storage. Sucrose storage was characterized by carbon derived from 14C-sucrose uptake being partitioned into the sucrose fraction with little evidence of further metabolism. The onset of storage was accompanied by the appearance of sucrose synthetase activity (Vmax 12 Mmol/h per mg protein; Km 7 mM). Neither sucrose phosphate synthetase nor alkaline invertase activities were detected during beet development. Intact sugar beet plants (containing a 100 g beet) exported 70% of the translocate to the beet, greater than 90% of which was retained as sucrose with little subsequent conversions.