Title

Phloem Unloading in Developing Leaves of Sugar Beet: I. Evidence for Pathway through the Symplast

Document Type

Article

Publication Date

9-1-1985

Publication Source

Plant Physiology

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 of14C-label into sink leaves during steady state labeling of a source leaf with14CO2. 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.

Inclusive pages

237-241

ISBN/ISSN

0032-0889

Publisher

American Society of Plant Biologists

Volume

79

Peer Reviewed

yes