Evidence for the Presence of a Sucrose Carrier in Immature Sugar Beet Tap Roots

Abstract

The objectives of this work were to determine the path of phloem unloading and if a sucrose carrier was present in young sugar beet (Beta vulgaris L.) taproots. The approach was to exploit the characteristics of the sucrose analog, l'-fluorosucrose (F-sucrose) The pathway of sucrose unloading in various sink organs has been extensively studied. In species such as corn and sugar cane where sucrose unloading occurs by way of the apoplast and a cell-wall acid invertase is present, sucrose hydrolysis is believed to be essential, because hexoses are the major transport sugars (10,19).In mature sugar beet taproot, sucrose unloading is apoplastic and uptake and accumulation in the vacuole occurs without hydrolysis (23). In immature roots, however, the pathway of sucrose unloading and its movement into the sink parenchyma cells has not been determined. Furthermore, due to the presence of wall-bound invertase activity in this tissue, the relative importance of invertase and the presence of a sucrose-specific carrier at the plasmalemma, i.e., the requirement for hydrolysis prior to uptake, are not known. In the case of apoplastic sucrose unloading in immature roots, sucrose may follow a different fate than that in the mature tissue in which wall-bound invertase activity is negligible.The objectives of the present work were twofold. First, to determine whether sucrose unloading in immature sugar beet taproot is apoplastic or symplastic and, second, to determine whether a sucrose carrier is present at this stage of growth. For this purpose we used young sugar beet roots at two different '

Sugar metabolism ofVetiveria zizanioidescells cultured with Amberlite XAD-4. Uptake of radiolabelled sugars, cell wall invertase activity and gene expression

“…The uptake of sucrose, despite the increased expression and activity of the CWI, suggests that sucrose hydrolysis, though important, is not essential for sugar assimilation in V. zizanioides cell cultures (in accordance with Lemoine et al 1988;Shin et al 2003).…”

Evidence for the Uptake of Sucrose Intact into Sugarcane Internodes

“…A group translocator for sucrose uptake has also been proposed for beet roots (9,19) and grape berries (5). However, there is some evidence that the uridine 5 '-diphosphoglucose group transporter is not the sole sucrose transport mechanism in sugarbeet roots (13). Also, studies on sugar uptake in the stem tissue of sweet sorghum, a plant closely related to sugarcane, showed sucrose cleavage was not required for transport into the vacuole (14).…”

Application of the Software e-SAFES® (Based on SAFES Methodology) to Control Disinfection in the Sugar Extraction from Sugar Beet (Beta vulgaris L.)

“…Together they form the tubular system called xylem (Steinert et al, 1990). Sugar is synthesized in the leaves of sugar beet and it is transported through the phloem to the root (Lemoine et al, 1988). While the diffusion of sucrose from the cell wall through the membrane of adjacent cells within the cytoplasm is moderately impaired, the vacuole membrane presents a barrier in which the permeability to sucrose is extremely low (Ehwald, 1980).…”