Phloem loading in Coleus blumei in the absence of carrier-mediated uptake of export sugar from the apoplast. [Coleus blumei Benth]

Journal Article · Thu Nov 01 00:00:00 EST 1990 · Plant Physiology; (USA)

DOI:https://doi.org/10.1104/pp.94.3.1244· OSTI ID:5627825

Turgeon, R; Gowan, E ^[1]

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1. Cornell Univ., Ithaca, NY (USA)

Phloem loading in Coleus blumei Benth. leaves cannot be explained by carrier-mediated transport of export sugar from the apoplast into the sieve element-companion cell complex, the mechanism by which sucrose is thought to load in other species that have been studied in detail. Uptake profiles of the export sugars sucrose, raffinose, and stachyose into leaf discs were composed of two components, one saturable and other other not. Saturable (carrier-mediated) uptake of all three sugars was almost completely eliminated by the inhibitor p-chloromercuribenzenesulfonic acid (PCMBS). However, when PCMBS was introduced by transpiration into mature leaves it did not prevent accumulation of {sup 14}C-photosynthate in minor veins or translocation of labeled photosynthate from green to nonchlorophyllous regions of the leaf following exposure to {sup 14}CO{sub 2}. The efficacy of introducing inhibitor solutions in the transpiration stream was proven by observing saffranin O and calcofluor white movement in the minor veins and leaf apoplast. PCMBS introduced by transpiration completely inhibited phloem loading in tobacco leaves. Phloem loading in C. blumei was also studied in plasmolysis experiments. The carbohydrate content of leaves was lowered by keeping plants in the dark and then increased by exposing them to light. The solute level of intermediary cells increased in the light (phloem loading) in both PCMBS-treated and control tissues. A mechanism of symplastic phloem loading is proposed for species that translocate the raffinose series of oligosaccharides.

• OSTI ID: 5627825
• Journal Information: Plant Physiology; (USA), Vol. 94:3; ISSN 0032-0889
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
PLANTS
METABOLISM
BIOLOGICAL PATHWAYS
CARBON 14 COMPOUNDS
CARBON DIOXIDE
INHIBITION
MERCURY COMPOUNDS
PHOTOSYNTHESIS
SACCHARIDES
TRACER TECHNIQUES
TRANSLOCATION
CARBOHYDRATES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
SYNTHESIS
550501* - Metabolism- Tracer Techniques