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Na + / myo ‐inositol symporters and Na + /H + ‐antiport in Mesembryanthemum crystallinum
Author(s) -
Chauhan Sanjay,
Forsthoefel Nancy,
Ran Yingquing,
Quigley Francoise,
Nelson Donald E.,
Bohnert Hans J.
Publication year - 2000
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2000.00903.x
Subject(s) - mesembryanthemum crystallinum , symporter , halophyte , antiporter , antiporters , vacuole , biology , biochemistry , arabidopsis , sodium , microbiology and biotechnology , chemistry , cytoplasm , transporter , salinity , membrane , gene , ecology , organic chemistry , mutant
Summary Mitr1 and Mitr2 from Mesembryanthemum crystallinum (common ice plant) are members of a family of genes homologous to H + [or Na + ]/myo‐inositol symporters (ITRs), not previously studied in plants. MITR1 complemented an Itr1 ‐deficient yeast strain. Mitr1 is strongly expressed in roots, moderately in stems, and weakly in leaves. Its transcripts increased in all organs, most dramatically in roots, under salinity stress. Mitr2 constitutes a rare transcript, slightly upregulated by salt stress in leaves only. Mitr1 transcripts are present in all cells in the root tip, but become restricted to phloem‐associated cells in mature roots. Peptide antibodies against the two proteins indicated the presence of MITR1 in all organs and of MITR2 in leaves. Both are located in the tonoplast. MITR1 acts in removing sodium from root vacuoles, correlated with findings of low root sodium, while leaf vacuoles accumulate sodium in the ice plant. Up‐regulation in leaves and stems is also found for Na + /H + ‐antiporter ( Nhx ‐type) transcripts. Under comparable stress conditions, Nhx‐ and Itr ‐like transcripts in Arabidopsis were regulated differently. In the ice plant, co‐ordinate induction of Na + /H + ‐antiporters and Na + /myo‐inositol symporters transfers sodium from vacuoles in root cells into the leaf mesophyll as a halophytic strategy that lowers the osmotic potential. The tissue‐specific differential expression of Itr ‐ and Nhx ‐type transcripts suggests that the vacuolar sodium/inositol symporters function to reduce sodium amounts in cells of the root and vascular tissue, while sodium/proton antiporters in leaf tissues function to partition sodium into vacuoles for storage.