The energy cost of the tonoplast futile sodium leak

Summary Active removal of Na + from the cytosol into the vacuole plays a critical role in salinity tissue tolerance, but 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, could 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 on a phylogenetic and bioinformatic analysis of the plant two‐pore channel family and the difference in its structure and regulation between halophytes and glycophytes, in the context of salinity tolerance.