JXB Advance Access originally published online on November 22, 2006
Journal of Experimental Botany 2007 58(3):377-390; doi:10.1093/jxb/erl203
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© 2006 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Water permeability differs between growing and non-growing barley leaf tissues
1Division of Biological Sciences, University of Paisley, Paisley, PA1 2BE, Scotland, UK
2Unité de Biochimie Physiologique, Institut des Sciences de la Vie, Université catholique de Louvain, Croix du Sud 5–15, B-1348 Louvain-la-Neuve, Belgium
3Unité d'écophysiologie et amélioration végétale, Université catholique de Louvain, Croix du Sud 1–10, B-1348 Louvain-la-Neuve, Belgium
4The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food & Environmental Quality Science, The Hebrew University of Jerusalem, Rehovot, 76100 Israel
5UCD School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland
* To whom correspondence should be addressed in Ireland. E-mail: wieland02fricke{at}yahoo.co.uk
A pressure probe technique and an osmotic swelling assay were used to compare water transport properties between growing and non-growing tissues of leaf three of barley. The epidermis was analysed in planta by pressure probe, whereas (predominantly) mesophyll protoplasts were analysed by osmotic swelling. Hydraulic conductivity (Lp) and, by implication, water permeability (Pf) of epidermal cells was 31% higher in the leaf elongation zone (Lp=0.5±0.2 µm s–1 MPa–1; Pf=65±25 µm s–1; means ±SD of n=17 cells) than in the, non-growing, emerged leaf zone (Lp=0.4±0.1 µm s–1 MPa–1; Pf=50±15 µm s–1; n=24; P <0.05). Similarly, water permeability of mesophyll protoplasts was by 55% higher in the elongation compared with emerged leaf zone (Pf=13±1 µm s–1 compared with 8±1 µm s–1; n=57 and 36 protoplasts, respectively; P <0.01). Within the leaf elongation zone, a small population of larger-sized protoplasts could be distinguished. These protoplasts, which originated most likely from parenchymateous bundle sheath or midrib parenchyma cells, had a three-fold higher water permeability (P <0.001) as mesophyll protoplasts. The effect on Lp and Pf of known aquaporin inhibitors was tested with the pressure probe (Au+, Ag+, Hg2+, phloretin) and the osmotic swelling assay (phloretin). Only phloretin, when applied to protoplasts in the swelling assay caused an average decrease in Pf, but the effect varied between isolations. Technical approaches and cell-type and growth-specific differences in water transport properties are discussed.
Key words: Aquaporin, bundle sheath, epidermis, Hordeum vulgare, leaf cell elongation, mesophyll, pressure probe, protoplast, water permeability
Received 10 April 2006; Revised 6 September 2006 Accepted 19 September 2006
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