Nucleoside Diphosphate Levels in Taproots and Fibrous Roots of Beta vulgaris L. : Implifications for Control of Sucrose Allocation between Two Sinks

Sucrose synthase (EC 2.4.1.13) of sugarbeet (Beta vulgaris L.) fibrous roots has a distinctly different order of preference for nucleoside diphosphate substrates than that of the taproot enzyme (Silvius, Snyder 1979 Plant Physiol 64: 1070-1073). Separation and quantitation of UDP, ADP, and GDP in root extracts by high-pressure liquid chromatography revealed that UDP levels in taproot tissue were 5 to 10 times greater than those of fibrous root tissues. The lower fibrous root UDP levels were associated with significantly higher ADP and GDP levels in these roots as compared to the taproot. These differences are consistent with differences in the substrate affinity of sucrose synthase and suggest a regulatory role of the enzyme in the control of sucrose cleavage and utilization between the two root types.