Chapter title：Dynamic Responses of the Halophyte Suaeda maritima to Various Levels of External NaCl Concentration
Authors: Zhang JL*(张金林), Bai R, Flowers TJ, Wang CM, Wetson AM, Duan HR, He AL, Gurmani AR, Wang SM*
Book: Handbook of Halophytes, Springer International Publishing, Cham
Book author: Grigore MN
Abstract: Background and Aims Salinity is an increasingly serious problems for agricultural production worldwide. However, little is known about the dynamic responses of plants to salinity as most experiments report single time points after a salt treatment. So here, the aim of our work was to characterize the dynamic responses of the salt-accumulating halophyte Suaeda maritima to various NaCl concentrations which could aid in identifying the genes involved in salt tolerance. Methods Seedlings of S. maritima were treated with 25, 150, or 200 mM NaCl for various periods (0–480 h) before plant biomass, tissue water content, tissue Na+ concentration, 22Na+ influx, and tissue K+ concentration were measured. Results It was found that higher salinity (150 and 200 NaCl) significantly inhibited root growth during long-term treatments. Root Na+ concentrations reached their peak values of 140, 205, and 310 mM at 192, 240, and 360 h after treatments of 25, 150, and 200 mM NaCl, respectively, and then decreased slowly with the prolonging of salt treatments. However, shoot Na+ concentration increased sharply between 6 and 12 h after the three salinity treatments and then increased slowly to their peak values of 376, 616, and 715 mM after 480 h of the three salt treatments. 22Na+ influx was significantly higher in 150 and 200 mM NaCl concentrations than in 25 mM with obvious increases after 0.5 h and 12 h of treatment and subsequently remained stable or decreased slowly until the end of treatments. These results were consistent with the tissue Na+ concentrations (mM). In contrast, K+ concentrations decreased slowly in both roots and shoots such that by the end (480 h) of the three NaCl treatments, the reductions were 37%, 64%, and 54.5% in the shoots and 51%, 14.8%, and 5.4% in the roots, respectively, compared with that before treatment (0 h). Conclusions Consequently, we proposed that the coordinated regulation of K+ and Na+ plays an important role in the long-term survival of S. maritima from salinity and reducing root growth is another strategy to decrease net Na+ uptake; Na+ exclusion might also occur even in salt-accumulating halophytes when exposed to salt solution over the long term when sufficient Na+ has accumulated in its tissues.