Plant and Cell Physiology Advance Access published online on June 30, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm083
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HvPIP1;6, a Barley (Hordeum vulgare L.) Plasma Membrane Water Channel Particularly Expressed in Growing Compared to Non-growing Leaf Tissues
1Division of Biological Sciences, University Paisley, Paisley, PA1 2BE, Scotland, 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: Wieland Fricke. UCD School of Biology and Environmental Sciences, UCD Science Centre West, University College Dublin, Belfield, Dublin 4, Ireland. E-mail: wieland02fricke{at}yahoo.co.uk, Phone: +353-1-7162019, Fax: +353-1-7161153
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Abstract |
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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; Hollenbach and Dietz 1995) 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 three 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, PIP. Expression of HvPIP1;6 was highest in the elongation zone, where it accounted for more than 85% of expression of known barley PIP1s. Within the elongation zone, faster-grower regions showed higher expression than slower-growing ones. Expression of HvPIP1;6was confined to the epidermis, with some expression in neighbouring mesophyll cells. Expression of HvPIP1;6 in Xenopus laevis oocytes increased osmotic water permeability four- to six-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 abscisic acid. Plasma membrane preparations were analysed by Western blots using an antibody that recognised PIP1s. Levels of PIP1s were highest in 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
6Present address: The Institute of Subtropical Agro-ecology of Chinese Academy of Sciences, Changsha, China
7Corresponding author: E-mail, wieland02fricke{at}yahoo.co.uk, Fax, +353-1-7161153 The nucleotide sequence reported in this paper has been submitted to EMBL database under accession number CO720031.
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