The Rice monovalent cation transporter OsHKT2;4: Revisited ionic selectivity
The family of plant membrane transporters named HKT (for high-affinity K+ transporters) can be subdivided into subfamilies 1 and 2, which, respectively, comprise Na+-selective transporters and transporters able to function as Na+-K+ symporters, at least when expressed in yeast (Saccharomyces cerevisiae) or Xenopus oocytes. Surprisingly, a subfamily 2 member from rice (Oryza sativa), OsHKT2;4, has been proposed to form cation/K+ channels or transporters permeable to Ca2+ when expressed in Xenopus oocytes. Here, OsHKT2;4 functional properties were reassessed in Xenopus oocytes. A Ca2+ permeability through OsHKT2;4 was not detected, even at very low external K+ concentration, as shown by highly negative OsHKT2;4 zero-current potential in high Ca2+ conditions and lack of sensitivity of OsHKT2;4 zero-current potential and conductance to external Ca2+. The Ca2+ permeability previously attributed to OsHKT2;4 probably resulted from activation of an endogenous oocyte conductance. OsHKT2;4 displayed a high permeability to K+ compared with that to Na+ (permeability sequence: K+ . Rb+ _ Cs+ . Na+ _ Li+ _ NH4 +). Examination of OsHKT2;4 current sensitivity to external pH suggested that H+ is not significantly permeant through OsHKT2;4 in most physiological ionic conditions. Further analyses in media containing both Na+ and K+ indicated that OsHKT2;4 functions as K+-selective transporter at low external Na+, but transports also Na+ at high (.10 mM) Na+ concentrations. These data identify OsHKT2;4 as a new functional type in the K+ and Na+-permeable HKT transporter subfamily. Furthermore, the high permeability to K+ in OsHKT2;4 supports the hypothesis that this system is dedicated to K+ transport in the plant.
| Main Authors: | , , , , , , |
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| Format: | article biblioteca |
| Language: | eng |
| Subjects: | F61 - Physiologie végétale - Nutrition, L50 - Physiologie et biochimie animales, F60 - Physiologie et biochimie végétale, Oryza sativa, cytologie, propriété physicochimique, membrane cellulaire, potassium, sodium, calcium, Xenopus laevis, capacité d'échange ionique, http://aims.fao.org/aos/agrovoc/c_5438, http://aims.fao.org/aos/agrovoc/c_2091, http://aims.fao.org/aos/agrovoc/c_1521, http://aims.fao.org/aos/agrovoc/c_9693, http://aims.fao.org/aos/agrovoc/c_6139, http://aims.fao.org/aos/agrovoc/c_7145, http://aims.fao.org/aos/agrovoc/c_1196, http://aims.fao.org/aos/agrovoc/c_49063, http://aims.fao.org/aos/agrovoc/c_24864, |
| Online Access: | http://agritrop.cirad.fr/565900/ http://agritrop.cirad.fr/565900/1/document_565900.pdf |
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