AtNHX1 exchanger mediates potassium compartmentation in vacuoles of transgenic tomato

• Published in: The Plant journal : for cell and molecular biology 2010-02, Vol.61 (3), p.495-506
• Main Authors: Leidi, Eduardo O, Barragán, Verónica, Rubio, Lourdes, El-Hamdaoui, Abdelaziz, Ruiz, M. Teresa, Cubero, Beatriz, Fernández, José A, Bressan, Ray A, Hasegawa, Paul M, Quintero, Francisco J, Pardo, José M
• Format: Article
• Language: English
• Subjects: Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Biological and medical sciences; Cation Transport Proteins - genetics; Cation Transport Proteins - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Lycopersicon esculentum - genetics; Lycopersicon esculentum - metabolism; NHX; Plant biology; Plant physiology and development; Plants, Genetically Modified; Potassium - metabolism; potassium transport; salt tolerance; Sodium-Hydrogen Exchangers - genetics; Sodium-Hydrogen Exchangers - metabolism; tomato; Tomatoes; Transgenic plants; vacuole; vacuoles; Vacuoles - metabolism
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313X.2009.04073.x

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.