The AtNHX1 exchanger mediates potassium compartmentation in vacuoles of transgenic tomato.
NHX-type antiporters in the tonoplast have been reported to increase the salt tolerance of various plants species, and are thought to mediate the compartmentation of Na(+) in vacuoles. However, all isoforms characterized so far catalyze both Na(+)/H(+) and K(+)/H(+) exchange. Here, we show that AtNHX1 has a critical involvement in the subcellular partitioning of K(+), which in turn affects plant K(+) nutrition and Na(+) tolerance. Transgenic tomato plants overexpressing AtNHX1 had larger K(+) vacuolar pools in all growth conditions tested, but no consistent enhancement of Na(+) accumulation was observed under salt stress. Plants overexpressing AtNHX1 have a greater capacity to retain intracellular K(+) and to withstand salt-shock. Under K(+)-limiting conditions, greater K(+) compartmentation in the vacuole occurred at the expense of the cytosolic K(+) pool, which was lower in transgenic plants. This caused the early activation of the high-affinity K(+) uptake system, enhanced K(+) uptake by roots, and increased the K(+) content in plant tissues and the xylem sap of transformed plants. Our results strongly suggest that NHX proteins are likely candidates for the H(+)-linked K(+) transport that is thought to facilitate active K(+) uptake at the tonoplast, and the partitioning of K(+) between vacuole and cytosol.
Leidi
Eduardo O
EO
Instituto de Recursos Naturales y Agrobiología (IRNASE), Consejo Superior de Investigaciones Científicas, Reina Mercedes, 10, Sevilla - 41012, Spain.
Barragán
Verónica
V
Rubio
Lourdes
L
El-Hamdaoui
Abdelaziz
A
Ruiz
M Teresa
MT
Cubero
Beatriz
B
Fernández
José A
JA
Bressan
Ray A
RA
Hasegawa
Paul M
PM
Quintero
Francisco J
FJ
Pardo
José M
JM
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011188:Potassium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism*
D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; C117751:NHX1 protein, Arabidopsis; D017923:Sodium-Hydrogen Exchangers; D011188:Potassium