Symposium IV: Sensing and responding to water
Abs #
40002: Function and regulation of aquaporins in plant roots
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Presenter: |
Maurel, Christophe , maurel@ensam.inra.fr |
Authors | Maurel, Christophe (A) Boursiac, Yann (A) Javot, Hélène (A) Tournaire-Roux, Colette (A) Santoni, Véronique (A) Luu, Doan-Trung (A) Chen, Sheng (A) Vander Willigen, Clare (A) | | Affiliations: |
(A): CNRS / INRA Montpellier
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| Web Site: | http://www.bpmp.cnrs.fr/Groupes/Aquaporines%20anglais.htm | |
Aquaporins are water channel proteins that form a large multigenic family in plants, with 35 members in Arabidopsis thaliana. Several lines of evidence, based on a combination of molecular, physiological, and genetic approaches, will be presented to show that aquaporins play a major role in transcellular water flow and water uptake in the Arabidopsis root. The function of plasma membrane aquaporins (PIP) was investigated by analyzing knock-out mutants for PIP2;2, one of the most abundantly expressed PIP isoforms in roots. The hydraulic conductivity of root cortex cells was reduced by 25% in the mutants and the osmotic water permeability of their roots was decreased by 15% with respect to wild-type plants. Altogether, these data provide evidence for the contribution of a single aquaporin gene to root water uptake and suggest that very close aquaporin homologues have evolved with specific functions (Javot et al., 2003, Plant Cell, 15 : 509). Aquaporins also mediate the regulation of root hydraulic conductivity (Lpr) in response to a large variety of environmental stresses including salinity and anoxia. Macro-array hybridizations revealed that most of the highly expressed aquaporin genes showed a 60-75% decrease in their expression level, in the 4-6 h following exposure to salt. This result is consistent with the long-term down-regulation of Lpr by salt. However, down-regulation of aquaporin genes lagged behind inhibition of Lpr suggesting that other mechanisms such as salt-induced post-translational modifications of aquaporins may be involved in the early phase of Lpr inhibition. These are currently under investigation by using 2-dimensional gel electrophoresis and mass spectrometry (Santoni et al., 2003, Biochem. J. 373: 289). In another study, the whole root and cell bases for inhibition of root water uptake by anoxia were delineated and linked to cytosol acidosis. A novel molecular mechanism for aquaporin gating by cytosolic pH was uncovered, which permits coordinate inhibition of plasma membrane aquaporins and, as a consequence, a general block of root water transport (Tournaire-Roux et al., 2003, Nature 425: 393).
