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A cohesion/tension model for the gating of aquaporins allows estimation of water channel pore volumes in Chara

Title data

Ye, Qing ; Muhr, Jan ; Steudle, Ernst:
A cohesion/tension model for the gating of aquaporins allows estimation of water channel pore volumes in Chara.
In: Plant, Cell & Environment. Vol. 28 (2005) Issue 4 . - pp. 525-535.
ISSN 1365-3040
DOI: https://doi.org/10.1111/j.1365-3040.2004.01298.x

Abstract in another language

The water permeability (hydraulic conductivity; Lp) of turgid, intact internodes of Chara corallina decreased exponentially as the concentration of osmolytes applied in the medium increased. Membranes were permeable to osmolytes and therefore they could be applied on both sides of the plasma membrane at concentrations of up to 2.0 m (5.0 MPa of osmotic pressure). Organic solutes of different molecular size (molecular weight, MW) and reflection coefficients (sigma(s)) were used [heavy water HDO, MW: 19, sigma(s): 0.004; acetone, MW: 58, sigma(s): 0.15; dimethyl formamide (DMF), MW: 73, sigma(s): 0.76; ethylene glycol monomethyl ether (EGMME), MW: 76, sigma(s): 0.59; diethylene glycol monomethyl ether (DEGMME), MW: 120, sigma(s): 0.78 and triethylene glycol monoethyl ether (TEGMEE), MW: 178, sigma(s): 0.80]. The larger the molecular size of the osmolyte, the more efficient it was in reducing cell Lp at a given concentration. The residual cell Lp decreased with increasing size of osmolytes. The findings are in agreement with a cohesion/tension model of the osmotic dehydration of water channels (aquaporins; AQPs), which predicts both reversible exponential dehydration curves and the dependence on the size of osmolytes which are more or less excluded from AQPs (Ye, Wiera T Steudle, Journal of Experimental Botany 55, 449-461, 2004). In the presence of big osmolytes, dehydration curves were best described by the sum of two exponentials (as predicted from the theory in the presence of two different types of AQPs with differing pore diameters and volumes). AQPs with big diameters could not be closed in the presence of osmolytes of small molecular size, even at very high concentrations. The cohesion/tension theory allowed pore volumes of AQPs to be evaluated, which was 2.3 +/- 0.2 nm(3) for the narrow pore and between 5.5 +/- 0.8 and 6.1 +/- 0.8 nm(3) for the wider pores. The existence of different types of pores was also evident from differences in the residual Lp. Alternatively, pore volumes were estimated from ratios between osmotic (P-f) and diffusional (P-d) water flow, yielding the number of water molecules (N) in the pores. N-values ranged between 35 and 60, which referred to volumes of 0.51 and 0.88 nm(3)/pore. Values of pore volumes obtained by either method were bigger than those reported in the literature for other AQPs. Absolute values of pore volumes and differences obtained by the two methods are discussed in terms of an inclusion of mouth parts of AQPs during osmotic dehydration. It is concluded that the mouth part contributed to the absolute values of pore volumes depending on the size of osmolytes. However, this can not explain the finding of the existence of two different types or groups of AQPs in the plasma membrane of Chara.

Further data

Item Type: Article in a journal
Refereed: Yes
Additional notes: BAYCEER33569
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: 18 Jun 2015 06:36
Last Modified: 18 Jun 2015 06:36
URI: https://eref.uni-bayreuth.de/id/eprint/15284