Purified vesicles of tobacco cell vacuolar and plasma membranes exhibit dramatically different water permeability and water channel activity
AUTOR(ES)
Maurel, Christophe
FONTE
The National Academy of Sciences of the USA
RESUMO
The vacuolar membrane or tonoplast (TP) and the plasma membrane (PM) of tobacco suspension cells were purified by free-flow electrophoresis (FFE) and aqueous two-phase partitioning, with enrichment factors from a crude microsomal fraction of ≥4- to 5-fold and reduced contamination by other cellular membranes. For each purified fraction, the mean apparent diameter of membrane vesicles was determined by freeze-fracture electron microscopy, and the osmotic shrinking kinetics of the vesicles were characterized by stopped-flow light scattering. Osmotic water permeability coefficients (Pf) of 6.1 ± 0.2 and 7.6 ± 0.9 μm⋅s−1 were deduced for PM-enriched vesicles purified by FFE and phase partitioning, respectively. The associated activation energies (Ea; 13.7 ± 1.0 and 13.4 ± 1.4 kcal⋅mol−1, respectively) suggest that water transport in the purified PM occurs mostly by diffusion across the lipid matrix. In contrast, water transport in TP vesicles purified by FFE was characterized by (i) a 100-fold higher Pf of 690 ± 35 μm⋅s−1, (ii) a reduced Ea of 2.5 ± 1.3 kcal⋅mol−1, and (iii) a reversible inhibition by mercuric chloride, up to 83% at 1 mM. These results provide functional evidence for channel-mediated water transport in the TP, and more generally in a higher plant membrane. A high TP Pf suggests a role for the vacuole in buffering osmotic fluctuations occurring in the cytoplasm. Thus, the differential water permeabilities and water channel activities observed in the tobacco TP and PM point to an original osmoregulatory function for water channels in relation to the typical compartmentation of plant cells.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=21292Documentos Relacionados
- Immunolocalization of the mercurial-insensitive water channel and glycerol intrinsic protein in epithelial cell plasma membranes.
- Water Transport across Yeast Vacuolar and Plasma Membrane-Targeted Secretory Vesicles Occurs by Passive Diffusion
- Water and vapor permeability at different temperatures of poly (3-Hydroxybutyrate) dense membranes
- cGMP-dependent channel protein from photoreceptor membranes: single-channel activity of the purified and reconstituted protein.
- Induced Changes in Permeability of Plant Cell Membranes to Water