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The function of water channels in Chara: The temperature dependence of water and solute flows provides evidence for composite membrane transport and for a slippage of small organic solutes across water channels

Title data

Hertel, Annett ; Steudle, Ernst:
The function of water channels in Chara: The temperature dependence of water and solute flows provides evidence for composite membrane transport and for a slippage of small organic solutes across water channels.
In: Planta. Vol. 202 (1997) Issue 3 . - pp. 324-335.
ISSN 0032-0935
DOI: https://doi.org/10.1007/s004250050134

Abstract in another language

Using the cell pressure probe, the effects of temperature on hydraulic conductivity (Lp; osmotic water permeability), solute permeability (permeability coefficient, P-s), and reflection coefficients (sigma(s)) were measured on internodes of Chara corallina, Klein ex Willd., em R.D.W.. For the first time, complete sets of transport coefficients were obtained in the range between 10 and 35 degrees C which provided evidence about pathways of water and solutes as they move across the plasma membrane (water channel and bilayer arrays). Test solutes used to check for the selectivity of water channels were monohydric alcohols of different molecular size and shape (ethanol, n-propanol, iso-propanol, and tert-butanol) and heavy water (HDO). Within the limits of accuracy, Q(10) values for Lp and for the diffusive water permeability (P-d) were identical (Q(10) for Lp=1.29 +/- 0.17 (+/- SD; n = 15 cells) and Q(10) for P-d = 1.25 +/- 0.16 (n = 5 cells)). The Q(10) values were equivalent to activation energies of E-a = 16.8 +/- 6.4 and 16.6 +/- 10.0 kJ . mol(-1), respectively, which is similar to that of self-diffusion or of viscous flow of water. The Q(10) values and activation energies for P-s of the alcohols were significantly larger (ethanol: Q(10) = 1.68 +/- 0.16, E-a = 37.1 +/- 5.9 kJ . mol(-1); n-propanol: Q(10) = 1.75 +/- 0.40, E-a = 43.1 +/- 15.3 kJ . mol(-1) iso-propanol: Q(10) = 2.12 +/- 0.42, E-a = 52.2 +/- 14.6 kJ . mol(-1); tert-butanol: Q(10) = 2.13 +/- 0.56, E-a = 51.6 +/- 17.1 kJ . mol(-1); +/- SD, n = 5 to 6 cells). Effects of temperature on reflection coefficients were most pronounced. With increasing temperature, sigma(s) values of the alcohols decreased and those of HDO increased. The data indicate that water and solutes use different pathways when crossing the membrane. Ordinary and isotopic water use water channels and the other test solutes use the bilayer array (composite transport model of membrane). Changes in sigma(s) values with temperature were found to be a sensitive measure for the open/closed state of water channels. The decrease of sigma(s) with temperature was theoretically predicted from the temperature dependence of P-s and Lp. Differences between predicted and measured values of sigma(s) allowed estimation of the bypass flow (slippage) of solutes through water channels which did not completely exclude test solutes. The permeability of channels depended on the structure and size of test solutes. It is concluded that water channels are much less selective than is usually thought. Since water channels represent single-file or no-pass pores, solutes drag along considerable amounts of water as they diffuse across channels. This results in low overall values of sigma(s). The sigma(s) of HDO was extremely low. Its response to temperature was opposite to that for the sigma(s) of the alcohols. This suggested a stronger effect of temperature on the hydraulic (osmotic) than on the diffusive water flow across individual water channels, i.e. a differential sensitivity of different mechanisms to temperature.

Further data

Item Type: Article in a journal
Refereed: Yes
Additional notes: BAYCEER33658
Institutions of the University: Research Institutions > Research Centres > Bayreuth Center of Ecology and Environmental Research- BayCEER
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Biology > Chair Plant Ecology
Faculties
Faculties > Faculty of Biology, Chemistry and Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Biology
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 500 Science
Date Deposited: 24 Sep 2015 09:38
Last Modified: 24 Sep 2015 09:38
URI: https://eref.uni-bayreuth.de/id/eprint/19736