Study of characteristic response to salt-ion stresses of Salicornia europaea seedlings
Salicornia europaea seedlings were examined for their performance under different salt-ion stresses (-0. 88 MPa, Na+ , Cl- , NaCl) and for their tolerance to a wide range of NaCl concentrations (100-1 000 mmol/L) in the laboratory. The distributions of salts and ionic absorption in S. europaea under 100 - 1 000 mmol/L NaCl treatments were also studied. Treatments with different salts of the same osmotic potential for 12 days all promoted growth of S. europaea seedlings, with the best effect from the NaCl treatment. When plants were treated for 24 days, growth of S. europaea seedlings was still stimulated under treatments of Cl- a-lone or NaCl, while growth was inhibited under Na+ stress. The growth under NaCl was much better than that under the Cl- alone treatment, suggesting that both Na+ and Cl- were beneficial elements for the growth of S. europaea seedlings. Our results also showed that 300 - 400 mmol/L NaCl was the optimum concentration for growth. K+ content in roots did not show significant change at less than 100 - 200 mmol/L NaCl, and Na+ content in roots did not change at less than 100 mmol/L NaCl. As NaCl concentration was increased (> 200 mmol/L), K+ content in roots decreased markedly. When NaCl was above 700 mmol/L, K+ content in roots did not decrease further. Root SK, Na increased greatly with an increase in NaCl concentration, suggesting that K+ absorptive selectivity was higher under NaCl treatments. In S. europaea shoots, K+ content was decreased at low concentrations of NaCl but did not decrease further when NaCl in the medium exceeded 200 mmol/L. The results suggested that maintaining K+ homeostasis was a notable characteristic of S. europaea shoots. We conclude that an increase in K+ absorptive selectivity in roots and maintenance of K+ homeostasis in shoots may contribute to S. europaea's tolerance to high salt concentrations, implying the existence of unique Na+ , K+ absorptive carriers or channel systems in S. europaea.
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