Characteristics of Sucrose Transport and Sucrose-Induced H+ Transport on the Tonoplast of Red Beet (Beta vulgaris L.) Storage Tissue

Abstract

Sucrose-induced changes of the energization state of the red beet root (Beta vulgaris L. ssp. conditiva) vacuolar membrane were observed with the fluorescent dyes 6-chloro-9-{[4-(diethylamino)-1 -methylbutyll-aminol-2-methoxyacridine dihydrochloride, as a pH monitor, and 9-amino-6-chloro-2-methoxyacridine (ACMA). Consequently, transient acidification of the surrounding suspension medium could be measured with a pH electrode. This signal was specific for Suc and was not seen for sorbitol, mannitol, or maltose. Sucrose-induced medium acidification was sensitive to the same inhibitors that were efficient i n inhibiting sucrose transport, including the monoclonal antibodies TNP, , -, , and C50-5.3. It was seen with vacuoles and vesicles energized with MgATP before sucrose was added but also with vacuoles not artificially energized previously. Using bafilomycin A, for the inhibition of the vacuolar ATPase of vacuoles previously energized by MgATP, apparent K, values for H + export from the vacuoles to the medium could be calculated taking into account the passive proton leak. Apparent K, values for H + export determined from data obtained with pH measurements in the medium and with ACMA corresponded to those obtained previously for sucrose uptake. Comparing sucrose uptake rates with corresponding H+ export rates at the respective sucrose concentrations and at K , , a stoichiometry of approximately one proton per transported sucrose was estimated.

Different Energization Mechanisms Drive the Vacuolar Uptake of a Flavonoid Glucoside and a Herbicide Glucoside

“…Attempts to demonstrate a proton extrusion induced by isovitexin using intact vacuoles or tonoplast vesicles and the pH-sensitive fluorescent dye 9-amino-6-chloro-2-methoxyacridine, as recently shown by Getz and Klein (26) for the sucrose/ H ϩ -antiporter of red beet storage parenchyma, failed due to chemical interaction of the dye with the flavonoid. However, as the isovitexin uptake rate is also reduced in the presence of valinomycin, a K ϩ -ionophore known to dissipate the membrane potential, flavonoid glucoside transport may also be coupled to that of K ϩ .…”

Metabolism and Accumulation of Sugars Translocated to Fruit and Their Regulation

“…Therefore, a sugar transporter coupled with energy on the tonoplast, i.e., an H + /sugar antiporter, is needed. The presence of this transporter was found by using isolated vacuoles (Yamaki, 1987) or tonoplast vesicles (Getz, 1991;Getz and Klein, 1995;Greuter and Keller, 1993). Recently, the gene of this sugar transporter localized on the tonoplast has been cloned (Endler et al, 2006;Wormit et al, 2006), although many genes of H + /sugar co-transporters localized on the plasma membrane have already been cloned from various plants, and their properties and functions have been clarified.…”

SWEET17, a Facilitative Transporter, Mediates Fructose Transport across the Tonoplast of Arabidopsis Roots and Leaves

“…Some agriculturally important crops such as sugar beet (Beta vulgaris; Leigh, 1984;Getz and Klein, 1995), citrus (Citrus spp. ; Echeverria and Valich, 1988), sugarcane (Saccharum officinarum; Thom et al, 1982), and carrot (Daucus carota; Keller, 1988) can store considerable amounts (.10% of plant dry weight) of Suc, Glc, or Fru in vacuoles of the storage parenchyma.…”