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Ratio of sugar concentrations in the phloem sap and the cytosol of mesophyll cells in different tree species as an indicator of the phloem loading mechanism
- Source :
- Planta. 248:661-673
- Publication Year :
- 2018
- Publisher :
- Springer Science and Business Media LLC, 2018.
-
Abstract
- Sucrose concentration in phloem sap was several times higher than in the cytosol of mesophyll cells. The results suggest that phloem loading involves active steps in the analyzed tree species. Phloem loading in source leaves is a key step for carbon partitioning and passive symplastic loading has been proposed for several tree species. However, experimental evidence to prove the potential for sucrose diffusion from mesophyll to phloem is rare. Here, we analyzed three tree species (two angiosperms, Fagus sylvatica, Magnolia kobus, and one gymnosperm, Gnetum gnemon) to investigate the proposed phloem loading mechanism. For this purpose, the minor vein structure and the sugar concentrations in phloem sap as well as in the subcellular compartments of mesophyll cells were investigated. The analyzed tree species belong to the open type minor vein subcategory. The sucrose concentration in the cytosol of mesophyll cells ranged between 75 and 165 mM and was almost equal to the vacuolar concentration. Phloem sap could be collected from F. sylvatica and M. kobus and the concentration of sucrose in phloem sap was about five- and 11-fold higher, respectively, than in the cytosol of mesophyll cells. Sugar exudation of cut leaves was decreased by p-chloromercuribenzenesulfonic acid, an inhibitor of sucrose-proton transporter. The results suggest that phloem loading of sucrose in the analyzed tree species involves active steps, and apoplastic phloem loading seems more likely.
- Subjects :
- 0106 biological sciences
0301 basic medicine
Sucrose
Plant Science
Phloem
01 natural sciences
Trees
03 medical and health sciences
chemistry.chemical_compound
Cytosol
Gymnosperm
Fagus sylvatica
Botany
Fagus
Genetics
Sugar
Plant Proteins
biology
Chemistry
fungi
Membrane Transport Proteins
food and beverages
Biological Transport
Magnolia kobus
Gnetum
biology.organism_classification
Apoplast
Plant Leaves
030104 developmental biology
Magnolia
Vacuoles
Mesophyll Cells
Sugars
010606 plant biology & botany
Subjects
Details
- ISSN :
- 14322048 and 00320935
- Volume :
- 248
- Database :
- OpenAIRE
- Journal :
- Planta
- Accession number :
- edsair.doi.dedup.....52a167fad9661d6904ae0f0e5f077462