Details

Autor(en) / Beteiligte

• Steudle, Ernst
• Henzler, Tobias

Titel

Water channels in plants: do basic concepts of water transport change?

Ist Teil von

• Journal of experimental botany, 1995-09, Vol.46 (9), p.1067-1076

Ort / Verlag

Oxford: Oxford University Press

Erscheinungsjahr

1995

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• A review and re-examination of literature data shows that highly selective water channels (aquaporins) have marked effects on the overall transport properties of the plasma membrane of plant cells. The application of the channel blocker HgCl2 (50 μM) or of high external concentrations of permeating solutes reduced the water permeability (hydraulic conductivity, Lp) of Chara internodes down to 25% of the control. In treated cells, reflection coefficients (σs) of permeating low molecular weight organic test solutes (alcohols, amides, ketones) were markedly reduced as well, but solute permeability (permeability coefficient, Ps) remained constant. A similar relation between Lp and σs was found with untreated cells of isolated epidermis of Tradescantia virginiana. The results can not be interpreted in terms of conventional membrane models (pore or solubility membrane); for instance, the classical frictional pore model (Dainty and Ginzburg, 1963) fails to explain low σs of rapidly permeating solutes. The results fit into a model which treats the membrane as a composite structure with proteinaceous arrays (containing water channels) in parallel with lipid arrays (‘composite transport model’). Test solutes predominantly pass across the lipid array which was not affected by treatments. Water, however, largely uses the water channel array which was affected. When using heavy water (HDO) as an osmotic solute, the transport pattern changed as predicted by the model. As indicated by low channel reflection coefficients of test solutes, water channels did not completely exclude small uncharged molecules and do show some permeability for the test solutes used. Low σs values of water channels are interpreted by a single-file mechanism of water and solute flow. Absolute values of transport coefficients (Lp, Ps, σs) represent mixed values to which the different membrane arrays contribute according to concepts available from irreversible thermodynamics. The patchy structure of the cell membrane results in a circulation flow of water in the membrane. The fact that water channels can be triggered by factors such as heavy metals and high concentration suggests that water transport can be regulated by opening or closing water channels. The results have consequences for our basic understanding of osmosis and water transport in plants.