caa a22 4500 397520778 CHVBK 20180308164632.0 cr unu---uuuuu 161202e199509 xx s 000 0 eng 10.1093/jxb/46.9.1067 doi (NATIONALLICENCE)oxford-10.1093/jxb/46.9.1067 Water channels in plants: do basic concepts of water transport change? [Elektronische Daten] [Ernst Steudle, Tobias Henzler] 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. © Oxford University Press REVIEW ARTICLE nationallicence Chara nationallicence composite transport model nationallicence hydraulic conductivity nationallicence permeability coefficient nationallicence reflection coefficient nationallicence water channels nationallicence Steudle Ernst Lehrstuhl für Pflanzenökologie, Universität Bayreuth, D-95440 Bayreuth, Germany aut Henzler Tobias Lehrstuhl für Pflanzenökologie, Universität Bayreuth, D-95440 Bayreuth, Germany aut Journal of Experimental Botany Oxford University Press 46/9(1995-09), 1067-1076 0022-0957 46:9<1067 1995 46 exbotj https://doi.org/10.1093/jxb/46.9.1067 text/html Onlinezugriff via DOI 1 review-article jats NATIONALLICENCE 856 40 https://doi.org/10.1093/jxb/46.9.1067 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Steudle Ernst Lehrstuhl für Pflanzenökologie, Universität Bayreuth, D-95440 Bayreuth, Germany aut NATIONALLICENCE 700 1- Henzler Tobias Lehrstuhl für Pflanzenökologie, Universität Bayreuth, D-95440 Bayreuth, Germany aut NATIONALLICENCE 773 0- Journal of Experimental Botany Oxford University Press 46/9(1995-09), 1067-1076 0022-0957 46:9<1067 1995 46 exbotj Metadata rights reserved CC BY-NC-4.0 http://creativecommons.org/licenses/by-nc/4.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-oxford