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Updated: May 5, 2026

Measuring the Osmotic Water Permeability Coefficient Pf of Spherical Cells: Isolated Plant Protoplasts as an Example
Published on: October 8, 2014
Tonoplast fine structure and osmotic regulation in Porphyra umbilicalis
1Botanisches Institut der Tierärztlichen Hochschule Hannover, Bünteweg 17D, D-3000, Hannover 71, Federal Republic of Germany.
Abstract:
In Porphyra, an intertidal red alga, the fine structure of the tonoplast was studied by freeze-fracture electron microscopy. It was shown that density and size of intramembraneous particles on the protoplasmic fracture face vary with external osmotic potential. The frequency of particles grouped in size classes (calculated per cell) increases with increasing osmotic stress and shows a maximum in 3 to 4 x artificial seawater medium ASP12. It is concluded that the intensity of tonoplast transport, which probably is enhanced with increasing osmotic stress from 1 to 4 x media, is most likely correlated with a change in membrane fine structure of the tonoplast.
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