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.