Sodium-related partial stomatal closure and salt tolerance of Aster tripolium

•  When Aster tripolium is grown at high salinity, stomatal closure is induced by the presence of sodium ions in the apoplast surrounding the guard cells. The occurrence of this system in Aster tripolium and not in the closely related glycophyte Aster amellus suggests that it could be an important factor in the network of physiological attributes required for salt tolerance. •  Gas exchange and growth parameters were measured in Aster tripolium plants grown at different levels of salinity. A simple mechanistic model was constructed to test whether the Na-sensing feature of the guard cells was a realistic component of salinity tolerance. •  The model captured very well the behaviour of plants in terms of salt uptake and reduction of growth with increasing salinity. There was moderate variance between measured and modelled rates of decrease of conductance with increasing levels of salinity. •  No evidence was found to refute our hypothesis that stomatal closure in response to sodium plays an important role in salt tolerance of Aster tripolium.