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The strategy of Suaeda salsa adaptation to high salinity was shown in this study. Our results firstly demonstrated that Na+ was a beneficial element rather than toxic ion for S. salsa plants. The biomass of S. salsa seedlings increased significantly after salt-treatment (100–400 mmol/L NaCl). Secondly, S. salsa had strong ability to accumulate Na+ under saline condition. Ninety-four percent of Na+ absorbed by salt-treated S. salsa plant accumulated in the shoot, especially in the leaves, and 98% of Na+ in the leaves accumulated in leaf symplast. Thirdly, measurement on isolated tonoplast-enriched membrane vesicles derived from the leaves of S. salsa showed that increased V-H+-ATPase hydrolytic activity, V-H+-ATPase proton pump activity and the tonoplast Na+/H+ antiport activity were found in salt-treated leaves compared with the control leaves. Up-regulation of the tonoplast Na+/H+ antiport activity was due to increase of both transcription and translation. These results suggested that coordinate up-regulation of V-H+-ATPase activity and Na+/H+ antiporter activity play a pivotal role in Na+ sequestering into vacuoles of S. salsa.

The effects of salt stress (0–400 mM NaCl) on PSII photochemistry, photoinhibition and photosynthetic pigment composition were investigated in the halophyte Suaeda salsa grown under outdoor conditions and exposed to full sunlight. Salt stress resulted in a growth stimulation which was optimal at 200 mM NaCl. With increasing salt concentration, leaf water potential and evaporation rate decreased significantly while there were no changes in leaf relative water content. Salt stress also resulted in a significant accumulation of sodium and chloride in leaves. Salt stress induced neither effects on the maximal efficiency of PSII photochemistry measured either at predawn or at midday nor effects on the actual PSII efficiency ( Φ PSII ), the efficiency of excitation energy capture by open PSII reaction centres, photochemical quenching, and non-photochemical quenching (NPQ) at midday. No significant changes were observed in the contents of neoxanthin, lutein, β-carotene, violaxnthin, antheraxthin, zeaxanthin, chlorophyll a and b in salt-stressed plants. Our results suggest that S. salsa showed high resistance not only to salinity stress but also to photoinhibition even when treated with high salinity as high as 400 mM NaCl and exposed to full sunlight. The results indicate that tolerance of PSII to high salinity stress and high light stress can be viewed as an important strategy for S. salsa to grow in very high saline soil.