Na+/H+ transporters of the halophyte Mesembryanthemum crystallinum L.
Technische Universität, Darmstadt
[Ph.D. Thesis], (2008)
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|Item Type:||Ph.D. Thesis|
|Title:||Na+/H+ transporters of the halophyte Mesembryanthemum crystallinum L.|
The aim of this work was to understand the mechanisms of Na+ accumulation in the halophyte Mesembryanthemum crystallinum L. during NaCl induced transition from C3 photosynthesis to crassulacean acid metabolism (CAM). Under high salinity M. crystallinum is a strong salt includer accumulating high amounts of Na + in leaves. To understand the mechanisms of Na+ accumulation during NaCl adaptation Na+/H+ antiporters from leaves of M. crystallinum were cloned by RACE PCR. In silico analysis identified the five cloned antiporters as belonging to three different families of exchangers: NhaP/SOS1 family, represented by McSOS1; IT/NhaD, represented by McNhaD: IC-NHE/NHX, with McNHX1 and McNHX3 belonging to the vacuolar class I and McNHX2 to the endomembrane class II. McSOS1, McNhaD and McNHX1 are homologous to the Na+/H+ antiporters AtSOS1, AtNHX1-2 and AtNHD1 of Arabidopsis thaliana, which are located at the plasma membrane, tonoplast and plastidial membrane, respectively. Functional complementation tests in Saccharomyces cerevisiae revealed that McSOS1 and McNhaD can complement the Na+ sensitivity of a yeast mutant strain (ena1-4 nha1 nhx1). Out of the three cloned antiporters of the IC-NHE/NHX family only McHX1 was able to restore resistance to Hygromycin B in the yeast mutant strain nhx1 implying that only this antiporter functions at the vacuolar membrane. Real-time PCR analysis demonstrated that the expression level of McSOS1, McNhaD and McNHX1 increased under salt stress. This increase in expression level correlated with the accumulation of sodium in leaves suggesting a physiological role for the antiporters in Na+ compartmentation during adaptation to high salinity. In particular, analysis of salt accumulation on the cellular level revealed a high Na+ content not only in vacuoles but also in chloroplasts. Together with the observation that the cloned antiporter McNhaD is localized to the plastidial membrane this points to a hitherto unknown pathway of Na+ transport out of the cytosol. The integrated function of the Na+/H+ antiporter localized to the plasma membrane (McSOS1), the tonoplast (McNHX1) and the chloroplast membrane (McNhaD) will allow an immediate detoxification of the cytoplasm from Na+.
|Place of Publication:||Darmstadt|
|Classification DDC:||500 Naturwissenschaften und Mathematik > 580 Pflanzen (Botanik)|
|Divisions:||10 Department of Biology|
|Date Deposited:||31 Oct 2008 11:27|
|Last Modified:||18 Dec 2012 12:56|
|Referees:||Homann, PD Dr. Ulrike and Thiel, Prof. Dr. Gerhard|
|Refereed:||31 July 2008|
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