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.