Expression of a Suaeda salsa Vacuolar H+/Ca2+ Transporter Gene in Arabidopsis Contributes to Physiological Changes in Salinity

A cDNA (SsCAX1) encoding a tonoplast-localised Ca2+/H+ exchanger was isolated from a C3 halophyte Suaeda salsa (L.). To clarify the role of SsCAX1 in plant salt tolerance, Arabidopsis plants expressing SsCAX1 were treated with NaCl. Transgenic Arabidopsis plants displayed decreased salt tolerance. Although Na+ content was close to wild-type plants, transgenic plants accumulated more Ca2+ and retained less K+ in leaves than the wild-type plants in salinity. Furthermore, transgenic lines held higher leaf membrane leakage than wild-type lines under NaCl treatment. In addition, transgenic plants showed a 23% increase in vacuolar H+-ATPase activity compared with wild-type plants in normal condition. But the leaf V-H+-ATPase activity had subtle changes in transgenic plants, while significantly increased in wild-type plants under saline condition. These results suggested that regulated expression of Ca2+/H+ antiport was critical for maintenance of cation homeostasis and activity of V-H+-ATPase under saline condition.