Regulating root aquaporin function in response to changes in salinity

Rapid changes in soil salinity present plants with an osmotic stress. If the concentration of salt in the soil water is too high then water may flow from the plant roots back into the soil. As part of an adaptive response, the regulation of proteins associated withwater transport, such as aquaporins, is altered. The change in regulation of aquaporins in roots in response to salt treatments occurs at transcriptional and post-translational levels. Cell specific changes in aquaporin transcript levels, protein abundance, subcellular localisation, protein phosphorylation, and protein:protein interactions have been observed. It has recently been revealed that a subset of plant aquaporins can function both as water and as ion channels. Both Arabidopsis PIP2;1 and PIP2;2 function as water and ion channels in heterologous systems. AtPIP2;1 and AtPIP2;2 ionic conductance was carried by sodium (Na⁺), indicating that a subset of plant PIP2s could have a role in Na⁺ transport in plants. We show quantitatively how AtPIP2;1 may account for the calcium (Ca²⁺) and pH sensitive Arabidopsis root non-selective cation channel. Salt treatments are known to result in a change in AtPIP2;1 phosphorylation, and in Arabidopsis roots this is associated with internalisation of AtPIP2;1 into pre-vacuolar compartments. Here we review how the regulation of aquaporins, in particular PIP2s, changes in root tissues in response to salt treatments.