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Sucrose uptake by the phloem parenchyma of carrot storage root

The characteristics of sucrose uptake into the symplast of phloem tissue discs harvested from fresh, actively-growing carrot storage roots are described. Sucrose uptake exhibited a curvilinear response with increasing sucrose concentration. The inhibitors p-chloromercuribenzenesulphonic acid (PCMBS)...

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Bibliographic Details
Published in:Journal of experimental botany 1994-01, Vol.45 (1), p.7-15
Main Authors: Hole, C.C., Dearman, Jane
Format: Article
Language:English
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Summary:The characteristics of sucrose uptake into the symplast of phloem tissue discs harvested from fresh, actively-growing carrot storage roots are described. Sucrose uptake exhibited a curvilinear response with increasing sucrose concentration. The inhibitors p-chloromercuribenzenesulphonic acid (PCMBS) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) decreased uptake and resulted in solely linear relationships between uptake and sucrose concentration. These results suggest that active carrier-mediated transport occurs at the plasmalemma in addition to a diffusive mechanism. The former saturates at a lower concentration (approximately 20 mM) than the latter which does not saturate below 100 mM. Though similar in their effect on the ethanol-soluble fraction, CCCP and PCMBS had different effects on the conversion of sucrose to ethanol-insoluble material. Varying the osmotic environment with different mannitol concentrations did not affect uptake between 0 and 400 mM mannitol, but did cause an increase at 600 mM mannitol: an effect which may have been an artefact of plasmolysis. Metabolic conversion to ethanol-insoluble forms remained unchanged from 0 to 250 mM mannitol and declined above this. Thus metabolism, but not uptake may be responsive to changes in turgor.
ISSN:0022-0957
1460-2431
DOI:10.1093/jxb/45.1.7