A Ca(2+)-sensitive system mediates low-affinity K(+) uptake in the absence of AKT1 in Arabidopsis plants.
K(+) acquisition by Arabidopsis roots is mainly mediated by the high-affinity K(+) transporter AtHAK5 and the inward-rectifier K(+) channel AtAKT1. This model is probably universal to plants. Mutant plants lacking these two systems (athak5,atakt1) take up K(+) and grow when the external K(+) concentration is above a certain level, indicating that an additional transport system may compensate for the absence of AtHAK5 and AtAKT1. Here we describe that this alternative system is essential for providing sufficient K(+) to sustain growth of athak5,atakt1 plants. This system is especially sensitive to Ca(2+), Mg(2+), Ba(2+) and La(3+), it transports Cs(+) and its activity is reduced by cyclic nucleotides. These results suggest that a Ca(2+)-permeable voltage-independent non-selective cation channel, probably belonging to the cyclic nucleotide gated channel (CNGC) family, may provide the pathway for K(+) uptake in athak5,atakt1 plants. The genes encoding the two members of the CNGC family that have been described as mediating root K(+) uptake, AtCNGC3 and AtCNGC10, are not up-regulated in athak5,atakt1 plants, excluding overexpression of these genes as a compensatory mechanism. On the other hand, an increased driving force for K(+) in athak5,atakt1 plants due to a hyperpolarization of the membrane potential of its root cells is also discarded. The identification of this unknown system may provide tools to improve plant K(+) nutrition in conditions where AtAKT1 functionality is reduced, such as under salinity. In addition, this system may constitute an important pathway for accumulation of toxic cations such as Cs(+) or radiocesium ((137)Cs(+)), and could play a role in phytoremediation.
Departamento de Nutrición, CEBAS-CSIC, Campus de Espinardo, 30100 Murcia, Spain.
Fernando
F
Caballero
María A
MA
Botella
Lourdes
L
Rubio
José A
JA
Fernández
Vicente
V
Martínez
Francisco
F
Rubio
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002412:Cations / Q000378:metabolism / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018527:Hydroponics; D008564:Membrane Potentials; D009154:Mutation; D009712:Nucleotides, Cyclic / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism; D027961:Potassium-Hydrogen Antiporters; D054712:Salinity; D027981:Symporters / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; D002412:Cations; D054815:Cyclic Nucleotide-Gated Cation Channels; D009712:Nucleotides, Cyclic; D015221:Potassium Channels; D027961:Potassium-Hydrogen Antiporters; D027981:Symporters; C501258:potassium transporter, Arabidopsis; C074500:AKT1 protein, Arabidopsis; D011188:Potassium; D002118:Calcium