Plant and Cell Physiology Advance Access originally published online on August 1, 2008
Plant and Cell Physiology 2008 49(9):1294-1305; doi:10.1093/pcp/pcn104
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Effect of Low Root Temperature on Hydraulic Conductivity of Rice Plants and the Possible Role of Aquaporins
1 National Agricultural Research Center for Tohoku Region, Climate Change Research Team, Morioka, 020-0198 Japan
2 National Institute for Agro-environmental Sciences, Agro-Meteorology Division, Tsukuba 305-8604, Japan
3 Plant Biophysics/Biochemistry Research Laboratory, College of Agriculture, Ehime University, Matsuyama, 790-8566 Japan
4 Laboratory of Cell Dynamics, Graduate school of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan
*Corresponding author: E-mail, murai{at}affrc.go.jp; Fax, +81-19-641-7794.
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Abstract |
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The role of root temperature TR in regulating the water-uptake capability of rice roots and the possible relationship with aquaporins were investigated. The root hydraulic conductivity Lpr decreased with decreasing TR in a measured temperature range between 10°C and 35°C. A single break point (TRC = 15°C) was detected in the Arrhenius plot for steady-state Lpr. The temperature dependency of Lpr represented by activation energy was low (28 kJ mol–1) above TRC, but the value is slightly higher than that for the water viscosity. Addition of an aquaporin inhibitor, HgCl2, into root medium reduced osmotic exudation by 97% at 25°C, signifying that aquaporins play a major role in regulating water uptake. Below TRC, Lpr declined precipitously with decreasing TR (Ea = 204 kJ mol–1). When TR is higher than TRC, the transient time for reaching the steady-state of Lpr after the immediate change in TR (from 25°C) was estimated as 10 min, while it was prolonged up to 2–3 h when TR < TRC. The Lpr was completely recovered to the initial levels when TR was returned back to 25°C. Immunoblot analysis using specific antibodies for the major aquaporin members of PIPs and TIPs in rice roots revealed that there were no significant changes in the abundance of aquaporins during 5 h of low temperature treatment. Considering this result and the significant inhibition of water-uptake by the aquaporin inhibitor, we hypothesize that the decrease in Lpr when TR < TRC was regulated by the activity of aquaporins rather than their abundance.
Keywords: Aquaporin - Hydraulic conductivity - Rice - Root temperature
Abbreviations:
Ar, root surface area; Ea, Arrhenius activation energy; Jv, volumetric xylem sap flow per unit root surface area; LRT, low root temperature; LT, low temperature; Lpr, hydraulic conductivity of root; Lprs, steady state Lpr; Lprt, transient value of Lpr; NIP, Nod26-like intrinsic protein; PIP, plasma membrane intrinsic protein; SIP, small and basic intrinsic protein; TIP, tonoplast intrinsic protein; TR, root temperature; TRC, break point temperature in an Arrhenius plot; V, volumetric xylem sap flow from excised seminal root; 
P, applied pressure; 
s, difference in osmotic potential between the exudated xylem sap and the root medium; 
, reflection coefficient for nutrient salts in the xylem.
5These authors contributed equally to this work.
(Received June 27, 2008; Accepted July 8, 2008)
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