Expression of Arabidopsis CAX2 in tobacco. Altered metal accumulation and increased manganese tolerance

Metal transport from the cytosol to the vacuole is thought to be an important component of ion tolerance and of a plant's potential for use in phytoremediation. The Arabidopsis antiporter CAX2 (calcium exchanger 2) may be a key mediator of this process. CAX2 expression in yeast suppressed both Ca2+ and Mn2+ growth defects. A peptide-specific antibody to the antiporter reacted with a 39-kD protein from plant vacuolar membranes. Tobacco (Nicotiana tabacum) plants expressing CAX2 accumulated more Ca2+, Cd2+,and Mn2+ and were more tolerant to elevated Mn2+ levels. Expression of CAX2 in tobacco increased Cd2+ and Mn2+ transport in isolated root tonoplast vesicles. These results suggest that CAX2 has a broad substrate range and modulation of this transporter may be an important component of future strategies to improve plant ion tolerance.