The energy cost of the tonoplast futile sodium leak

While active removal of Na+ from the cytosol into the vacuole plays a critical role in salinity tissue tolerance, another often neglected component of this trait is Na+ retention in vacuoles. This retention is based on an efficient control of Na+‐permeable slow‐ and fast‐vacuolar channels that mediate the back‐leak of Na+ into cytosol and, if not regulated tightly, may result in a futile cycle. This Tansley insight summarizes our current knowledge of regulation of tonoplast Na+‐permeable channels and discusses the energy cost of vacuolar Na+ sequestration, under different scenarios. We also report phylogenetic and bioinformatic analysis of plant two‐pore channel (TPC) family and the difference in its structure and regulation between halophytes and glycophytes, in the context of salinity tolerance.