LUTTS, S*, J P MARTINEZ, M BAJJI, and J M KINET. Laboratory of Cytogenetic, Catholic University of Louvain, 5 (Bte13) Place Croix du Sud, 1348 Louvain-la-Neuve, Belgium. - Sodium implication in the response of the halophyte species Atriplex halimus L. to various abiotic stresses.
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