METABOLISM OF UDPG IN THE VACUOLAR FRACTION FROM THE STORAGE ROOT OF SUGAR-BEET

In connection with the search for a hypothetical UDPG translocator in the tonoplast of sucrose-storing cells, we studied utilization of UDP (C-14)G in vacuolar preparations isolated from sugar beet (Beta vulgaris L.) roots. The results indicated insignificant metabolization of this substrate with formation for the most part of glucose phosphates in the incubation medium, i.e., still before penetration of the organelles by UDPG. Paper chromatography of aqueous and SDS extracts of vacuolar preparations revealed incorporation of the label into a number of compounds, among which oligosaccharides of the raffinose series were identified, together with a disaccharide that is not sucrose. Among polymers, the bulk of the label was incorporated into beta-glucan and starch. It is hypothesized that metabolism of UDPG is associated with the presence of plastids even in purified vacuolar preparations. The conclusion is reached that the mechanism of vectorial synthesis of sucrose previously postulated for sugarcane and red table beet is also absent in sugar beet vacuoles.