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. 1985 Sep;79(1):237–241. doi: 10.1104/pp.79.1.237

Phloem Unloading in Developing Leaves of Sugar Beet 1

I. Evidence for Pathway through the Symplast

J Gougler Schmalstig 1,2, Donald R Geiger 1
PMCID: PMC1074858  PMID: 16664377

Abstract

Physiological and transport data are presented in support of a symplastic pathway of phloem unloading in importing leaves of Beta vulgaris L. (`Klein E multigerm'). The sulfhydryl reagent p-chloromercuribenzene sulfonic acid (PCMBS) at concentration of 10 millimolar inhibited uptake of exogenous [14C]sucrose by sink leaf tissue over sucrose concentrations of 0.1 to 5.0 millimolar. Inhibited uptake was 24% of controls. The same PCMBS treatment did not affect import of 14C-label into sink leaves during steady state labeling of a source leaf with 14CO2. Lack of inhibition of import implies that sucrose did not pass through the free space during unloading. A passively transported xenobiotic sugar, l-[14C]glucose, imported by a sink leaf through the phloem, was evenly distributed throughout the leaf as seen by whole-leaf autoradiography. In contrast, l-[14C]glucose supplied to the apoplast through the cut petiole or into a vein of a sink leaf collected mainly in the vicinity of the major veins with little entering the mesophyll. These patterns are best explained by transport through the symplast from phloem to mesophyll.

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239Fig. 1
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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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