Cytosolic pH root water transport during anoxic stress through gating of aquaporins

TOURNAIRE-ROUX C, SUTKA M, JAVOT H, GOUT E, GERBEAU P, LUU D, BLIGNY R, MAUREL C

NATURE

Macmillan Magazine Ltd

Lugar: London; Año: 2003 vol. 425 p. 393 - 397

0028-0836

Transient flooding of soils (water-logging) results in acute oxygen deprivation (anoxia) of plant roots and is a major problem for agriculture, during winter in temperate latitudes, or after irrigation1. One early response of plants to anoxia is down-regulation of water uptake mediated by inhibition of root water conductivity (Lpr)2-4. Such root behaviour is also observed in response to other stresses such as exposure to salinity or nutrient deprivation5. Water uptake by plant roots is in large part mediated by water channel proteins (aquaporins) of the Plasma membrane Intrinsic Protein (PIP) subgroup6-8 but it is still unclear how aquaporin function can be beneficial or deleterious for stress tolerance and/or recovery in plants7-9. The use of mercury, a general but unspecific blocker of aquaporins has revealed that in roots, aquaporins mediate stress-induced inhibition of Lpr4,5,10. However, the cellular mechanisms involved in this response and, more generally, the molecular bases of aquaporin gating in plants and animals still remain elusive. Phosphorylation controls stimulus-induced sub-cellular targeting of mammalian Aquaporin-2 (AQP2) 11,12 and regulates the activity of specific plant aquaporin isoforms in Xenopus oocytes13,14. When expressed in these cells, the activity of certain mammalian homologues (AQP0, AQP3, AQP6) is dependent on external pH15-17. In plants, the water channel activity of purified plasma membrane vesicles can also be regulated by protons18. In the present paper, we delineate the organ and cell bases for inhibition of root water uptake under anoxic stress and link them to a novel molecular mechanism for aquaporin regulation by cytosolic (cyt-) pH. This mechanism provides a tentative basis to explain the general inhibition of root water transport in stress conditions. Besides fundamental knowledge on aquaporin gating, our work also opens new routes to explore, in plants and animals19, pH-dependent signalling processes leading to regulation of water transport