RESUMO
In plants, cytosolic Ca2+ levels are tightly regulated, and changes in cytosolic Ca2+ have been implicated in converting numerous signals into adapted responses. Vacuolar ion transporters are thought to be key mediators of cytosolic Ca2+ concentrations. In an attempt to interpret the role of vacuolar Ca2+ transport in plant processes, we have expressed the yeast vacuolar Ca2+/H+ antiporter, VCX1, in Arabidopsis and tobacco. This transporter localizes to the plant vacuolar membrane. VCX1-expressing Arabidopsis plants displayed increased sensitivity to sodium and other ions. These ion sensitivities could be suppressed by addition of calcium to the media. VCX1-expressing plants demonstrated increased tonoplast-enriched Ca2+/H+ antiport activity as well as increased Ca2+ accumulation. These results suggest that VCX1 expression in Arabidopsis could be a valuable tool with which to experimentally dissect the role of Ca2+ transport around the plant vacuole.
Assuntos
Antiporters/genética , Arabidopsis/genética , Proteínas de Ligação ao Cálcio/genética , Proteínas de Transporte de Cátions , Proteínas Fúngicas/genética , Antiporters/metabolismo , Arabidopsis/efeitos dos fármacos , Arabidopsis/metabolismo , Cálcio/metabolismo , Cálcio/farmacologia , Proteínas de Ligação ao Cálcio/metabolismo , Expressão Gênica , Regulação da Expressão Gênica de Plantas , Fenótipo , Plantas Geneticamente Modificadas/efeitos dos fármacos , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/metabolismo , Plantas Tóxicas , Saccharomyces cerevisiae/genética , Nicotiana/genéticaRESUMO
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 Ca(2+) and Mn(2+) 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 Ca(2+), Cd(2+), and Mn(2+) and were more tolerant to elevated Mn(2+) levels. Expression of CAX2 in tobacco increased Cd(2+) and Mn(2+) 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.
