Examples of Halophyte Strategies to Avoid Salt Injury: Secretion and Dilution

Noomene SLEIMI


Halophytes adopt different strategies to tolerate high salt concentrations. Some species are able to compartmentalize Na+ and Cl- in their vacuoles (osmotic regulation), and others export these ions out of their leaf surface (secretion). In the present study, Suaeda fruticosa and Spartina alterniflora were cultivated on nutritive solution with added NaCl (300, 400 and 800 mM). Relative growth rate (RGR) decreased strongly in both halophytes when NaCl concentration in the medium exceeded 300 mM. Nevertheless, S. fruticosa showed higher RGR compared to S. alterniflora for all NaCl concentrations. K+ concentrations in tissues decreased as medium salinity was increased, particularly in shoots. These changes were associated to Na+ and Cl- accumulation. However, concentrations of Na+ and Cl- did not exceed 1.5 mmol g-1 DW in S. alterniflora, whereas they reached 10 mmol g-1 DW in S. fruticosa. The two halophytes exhibited different behaviour in response to high salinity. In S. fruticosa, salt tolerance was related mainly to high growth activity and higher water contents, permitting an efficient salt dilution in tissues, sufficient to avoid an excessive accumulation in shoot tissues. S. alterniflora was able to protect its tissues against excessive Na+ and Cl- accumulation by an avoidance strategy based on NaCl secretion by shoots. Our results showed that this secretion amounted to more than 60% of total NaCl uptake. Salt secretion by shoots, mainly insured by salt glands, seemed to be selective for Na+ as compared to K+. This selective secretion of Na+ assures a protection against an unbalanced nutrition.


Compartmentation, halophytes, salt, secretion, strategies

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