Salt Tolerance in the Halophyte Suaeda maritima L.Dum.: Abscisic Acid Concentrations in Response to Constant and Altered Salinity

Endogenous abscisic acid contents were measured by gas-liquid chromatography in shoots of Suaeda maritima growing both in the steady state over a range of salinities and over a time-course following an increase in the culture solution salinity of between approximately 100 and 400 mol m−3 NaCl. In steady-state plants, the ABA content was maximal in the absence of salt at 41 ng g−1 fr. wt., declining to a minimum at 200 mol m−3 NaCl of 24 ng g−1 fr. wt. Increase of culture solution salinity resulted in a marked increase in shoot ABA which was maximal after 6 h or 24 h in plants previously growing at 200 mol m−3 NaCl and in the absence of salt, respectively. Additionally, culture solution water potentials were lowered by 1.0 MPa (equivalent to raising the salt concentration by around 200 mol m−3); this resulted in a similar increase in endogenous ABA content to that brought about by an iso-osmotic salt increase. Results are discussed in relation to the possible role of ABA in halophyte salt tolerance mechanisms.