Sucrose transport and phloem unloading in stem of Vicia faba: possible involvement of a sucrose carrier and osmotic regulation
After pulse labeling of a source leaf with /sup 14/CO/sub 2/, stem sections of Vicia faba plants were cut and the efflux characteristics of /sup 14/C-labeled sugars into various buffered solutions were determined. Radiolabeled sucrose was shown to remain localized in the phloem and adjacent phloem parenchyma tissues after a 2-hour chase. Therefore, sucrose leakage from stem segments prepared following a 75-minute chase period was assumed to be characteristic of phloem unloading. The efflux of /sup 14/C assimilates from the phloem was enhanced by 1 millimolar p-chloromercuribenzene sulfonic acid (PCMBS) and by 5 micromolar carbonyl cyanide m-chlorophenly hydrazone (CCCP). However, PCMBS inhibited and CCCP enhanced general leakage of nonradioactive sugars from the stem segments. Sucrose at concentrations of 50 millimolar in the free space increased efflux of (/sup 14/C)sucrose, presumably through an exchange mechanism. This exchange was inhibited by PCMBS and abolished by 0.2 molar mannitol. Increasing the osmotic concentration of the efflux medium with mannitol reduced (/sup 14/C)sucrose efflux. However, this inhibition seems not to be specific to sucrose unloading since leakage of total sugars, nonlabeled sucrose, glucose, and amino acids from the bulk of the tissue was reduced in a similar manner. The data suggest that phloem unloading in cut stem segments is consistent with passive efflux of sucrose from the phloem to the apoplast and that sucrose exchange via a membrane carrier may be involved.
- Research Organization:
- Utah State Univ., Logan
- OSTI ID:
- 7023533
- Journal Information:
- Plant Physiol.; (United States), Vol. 81:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SACCHAROSE
BIOCHEMICAL REACTION KINETICS
VICIA
PHYSIOLOGY
BIOLOGICAL PATHWAYS
CARBON 14 COMPOUNDS
CARBON DIOXIDE
OSMOSIS
PLANT STEMS
TRACER TECHNIQUES
BACTERIA
CARBOHYDRATES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
DIFFUSION
DISACCHARIDES
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
LEGUMINOSAE
MICROORGANISMS
OLIGOSACCHARIDES
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLANTS
REACTION KINETICS
RHIZOBIUM
SACCHARIDES
551001* - Physiological Systems- Tracer Techniques