Abstract
The uptake of sucrose into isolated discs cut from sink (growing) and source (sprouting) potato (Solanum tuberosum L.) tuber tissue was studied. The uptake of sucrose into sink-tuber discs demonstrated biphasic kinetics. The large saturable component was inhibited by incubation of the discs with p-chloromercuribenzene sulfonic acid (PCMBS) whilst both the saturable and linear components were inhibited by carbonyl cyanide m-chlorophenylhydrazone (CCCP). By contrast, in source-tuber discs, the linear component represented the majority of sucrose taken up, the saturable component playing only a minor role. In source discs, only the saturable component of uptake was inhibited by either PCMBS or CCCP. A large proportion (up to 25%) of sucrose taken up into sink-tuber discs was converted to starch but as the tubers aged the proportion of sucrose converted to starch decreased to the level found in source-tuber discs (approx. 3%). By contrast with sink-tuber discs (see Oparka and Wright, 1988b, Planta 175, 520–526) sucrose uptake into source discs was insensitive to turgor and demonstrated an uptake pattern similar to that of CCCP-treated sink tissue. It is proposed that exogenous sucrose is taken into the storage parenchyma of sink-tuber discs by both a carrier-mediated and a diffusional process. By contrast, uptake into the storage parenchyma of source-tuber discs appears to be essentially diffusional. The turgor sensitivity of sucrose uptake into sink-tissue discs may be mediated via the plasmalemma H+-ATPase. As the tuber ages the sucrose-uptake activity decreases and the capacity of the storage parenchyma to synthesise starch is lost. The data are discussed in relation to the in-vivo mechanisms of sucrose transport in storage tissues.
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Wright, K.M., Oparka, K.J. Sucrose uptake and partitioning in discs derived from source versus sink potato tubers. Planta 177, 237–244 (1989). https://doi.org/10.1007/BF00392812
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DOI: https://doi.org/10.1007/BF00392812