DNA coding for a Mg2+/H+ or Zn2+/H+ exchanger and transgenic plants expressing same

An isolated DNA molecule is provided coding for a polypeptide of the 11-12 transmembrane domain transporter family having a Mg2+/H+ or Zn2+/H+ exchange activity, herein designated MHX. The genomic MHX DNA was isolated from Arabidopsis thaliana cv. C-24. Transgenic plants transformed with said DNA and expressing MHX are shown to have a lower content of sodium as compared with corresponding wild-type plants or a higher dry matter weight upon growth in calcium-rich media as compared with corresponding wild-type plants. These transgenic plants are tolerant to stress conditions, particularly high salinity and calcium-rich media, e.g. saline and calcareous soils.