Facilitated Transport of Glucose in Isolated Phloem Segments of Celery

Abstract

In isolated phloem segments of celery (Apium graveolns L.), a tissue highly specific for sucrose and mannitol uptake, glucose uptake occurs at very low rates and exhibits biphasic kinetics. Nonpenetrating inhibitors such as parachloromercuribenzene sulfonic acid did not inhibit glucose uptake. However, uptake was greatly inhibited by penetrating inhibitors such as N-ethylmaleimide and carbonylcyanide-m-chlorophenyl hydrazone. Carbonylcyanide-m-chlorophenyl hydrazone inhibition of uptake was reversed by washing and addition of thiol reagents to uptake solutions. Phlorizin, a competitive inhibitor of glucose caused moderate inhibition of uptake only after 3 hours of tissue exposure. Low pH, fusicoccin, and low turgor which enhance H+-sugar cotransport did not alter uptake rates. Furthermore, glucose did not induce alkalinization of the uptake media. Efflux analysis indicated that the presence of 50 millimolar unlabeled glucose in the wash media enhanced exchange of the labeled glucose across the tonoplast. Results indicate that the glucose carrier is not located at the plasmalemma but appears to be present at the membrane of an intracellular compartment, most likely the tonoplast. Carrier-mediated glucose transport in this tissue is proposed to be a facilitated diffusion.

Selective interactions between different species of mycorrhizal fungi and Rhizobium meliloti strains, and their effects on growth, N2‐fixation (15N) and nutrition of Medicago sativa L.

“…The different types of plant material (different cultivars, growing conditions, age, freshness) and the different uptake conditions used could be responsible for this discrepancy. SH-reagent in certain tissues (Daie & Wilusz, 1987;Zambou & Spyropoulus, 1989). Table 1 shows that inclusion of DTT (5 ttiM) in the uptake medium indeed greatly reduced the inhibitory effect of CCCP (5 [IM) on uptake of 0-5 niM mannitol (from 57 to 19% inhibition).…”

Molecular Identification and Physiological Characterization of a Novel Monosaccharide Transporter from Arabidopsis Involved in Vacuolar Sugar Transport

“…Facilitated diffusion as well as energized proton antiport mechanisms have been described for monosaccharide and sucrose transport into isolated vacuoles or tonoplast vesicles prepared from a large number of plant species (Guy et al, 1979;Thom and Komor, 1984;Daie and Wilusz, 1987;Martinoia et al, 1987;Rausch, 1991;Shiratake et al, 1997). Accordingly, putative tonoplast-localized sugar carriers have been identified in proteomic approaches (Carter et al, 2004;Endler et al, 2006) or in immunological studies (Chiou and Bush, 1996).…”

Carbohydrate transport in discs of storage parenchyma of celery petioles

“…Data from experiments with surgically isolated phloem segments indicate that glucose uptake (most probably into the phloem parenchyma part of the mixed preparations) is biphasic and the saturable component is energy-independent, turgor-insensitive and contains functional SH-groups. Furthermore, the main glucose carrier of this tissue seems to be located at the tonoplast (and not at the plasmalemma) (Daie, 1987a, & b\ Daie & Wilusz, 1987. Our present data from experiments with pith parenchyma indicate that glucose uptake is also biphasic and the saturable component SH-group dependent, but in contrast to the phloem parenchyma, it is energy-dependent, turgor-sensitive and -to a good degree -located at the plasmalemma.…”