The Porosity of Permeabilised Chara Cells

When charophyte cells are plasmolysed at low temperature in the presence of the chelator EGTA, they lose turgor and stop streaming. Since cyclosis can be restored with exogenous ATP, the cells are described as permeabilised. In this study, the permeabilised cell is described in terms of the measured permeability of plasmalemma and cell wall to a series of fluorescent probes of increasing molecular weight. Cells were permeabilised according to standard procedures, and cyclosis was restored with exogenous ATP. The plasmalemma was not disintegrated, but rather a limited increase in porosity occurred, permitting the passage of molecules up to 874 daltons in weight. This indicates that permeabilisation induces the formation of pores with a maximum diameter close to 3 nm. The cell wall was permeable to molecules up to 4158 Da, indicating a maximum porosity close to 4.8 nm. Thus, the plasmalemma remains an important barrier to diffusion in permeabilised cells.