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Plant and Cell Physiology Advance Access originally published online on June 30, 2007
Plant and Cell Physiology 2007 48(8):1132-1147; doi:10.1093/pcp/pcm083
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© The Author 2007. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

HvPIP1;6, a Barley (Hordeum vulgare L.) Plasma Membrane Water Channel Particularly Expressed in Growing Compared with Non-Growing Leaf Tissues

Wenxue Wei1,6, Erik Alexandersson2, Dortje Golldack3, Anthony John Miller4, Per Ola Kjellbom2 and Wieland Fricke1,5,*

1Division of Biological Sciences, University of Paisley, Paisley PA1 2BE, UK
2Department of Plant Biochemistry, Lund University, PO Box 124, SE-22100 Lund, Sweden
3Lehrstuhl für Stoffwechselphysiologie und Biochemie der Pflanzen, Universität Bielefeld, Bielefeld, Germany
4Crop Performance and Improvement Division, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK
5School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland

*Corresponding author: E-mail, wieland02fricke{at}yahoo.co.uk; Fax, +353-1-7161153.


  Abstract

The aim of the present study was to identify water channel(s) which are expressed specifically in the growth zone of grass leaves and may facilitate growth-associated water uptake into cells. Previously, a gene had been described (HvEmip) which encodes a membrane intrinsic protein (MIP) and which is particularly expressed in the base 1 cm of barley primary leaves. The functionality of the encoding protein was not known. In the present study on leaf 3 of barley (Hordeum vulgare L.), a clone was isolated, termed HvPIP1;6, which has 99% amino acid sequence identity to HvEmip and belongs to the family of plasma membrane intrinsic proteins (PIPs). Expression of HvPIP1;6 was highest in the elongation zone, where it accounted for >85% of expression of known barley PIP1s. Within the elongation zone, faster grower regions showed higher expression than slower growing regions. Expression of HvPIP1;6 was confined to the epidermis, with some expression in neighboring mesophyll cells. Expression of HvPIP1;6 in Xenopus laevis oocytes increased osmotic water permeability 4- to 6-fold. Water channel activity was inhibited by pre-incubation of oocytes with 50 µM HgCl2 and increased following incubation with the phosphatase inhibitor okadaic acid or the plant hormone ABA. Plasma membrane preparations were analyzed by Western blots using an antibody that recognized PIP1s. Levels of PIP1s were highest in the elongation and adjacent non-elongation zone. The developmental expression profile of HvPIP2;1, the only known barley water channel belonging to the PIP2 subgroup, was opposite to that of HvPIP1;6.

Keywords: Barley (Hordeum vulgare L.) - Cell elongation zone - Epidermis - Leaf growth - Membrane intrinsic proteins - Plasma membrane water channel

Abbreviations: LHCb, light harvesting chlorophyll a/b-binding protein; MBS, modified Barth's saline; MIP, membrane intrinsic protein; NIP, NOD26-like intrinsic protein; OA, okadaic acid; PBS, phosphate-buffered saline; Pf, osmotic water permeability; PIP, plasma membrane intrinsic protein; SIP, small basic intrinsic protein; TIP, tonoplast intrinsic protein

6Present address: The Institute of Subtropical Agro-ecology of the Chinese Academy of Sciences, Changsha, PR China.

(Received May 24, 2007; Accepted June 21, 2007)
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