Atriplex halimus is a xero-halophyte species widespread in deserts of Mediterranean regions. The presence of this species is also reported on mining areas contaminated by heavy metals. In order to determine the physiological basis of resistance to ionic and water stresses, whole plants and calli obtained from hypocotyls, roots and shoots were exposed to various doses of NaCl, polyethyleneglycol, water shortage or heavy metals (Cd, Zn and Cu) under controlled environmental conditions. As expected NaCl, induced an increase in sodium content of both plants and cell cultures. Low NaCl doses (150 mM) clearly stimulated growth. Interestingly, plants and calli also specifically accumulated sodium in response to water stress. In vitro selection and physiological characterization of drought-sensitive and drought-resistant cell lines, as well as the poor performances of whole plants maintained in sodium-free nutrient solutions, confirmed that sodium accumulation is not a symptom of injury but may be part of an unusual physiological strategy of abiotic stress resistance. From a quantitative point of view, sodium accumulation did not significantly contribute to osmotic adjustment in water-stressed tissues. Sodium accumulation was observed on stressed calli maintained in the dark for several months. At the whole plant level, X-ray microanalysis revealed that increase in sodium concentration of cadmium-treated plants occurred mainly in leaf trichomes. These points suggest that the role of sodium in the resistance to ionic and water stresses in Atriplex halimus is not necessarily linked to the well-known implication of this element in the regulation of phosphoenolpyruvate translocation in C4 plants

Key words: Atriplex halimus, drought, halophyte, heavy metals, salinity, sodium