AUTHOR=Pan Ya-Qing , Guo Huan , Wang Suo-Min , Zhao Bingyu , Zhang Jin-Lin , Ma Qing , Yin Hong-Ju , Bao Ai-Ke 

TITLE=The Photosynthesis, Na+/K+ Homeostasis and Osmotic Adjustment of Atriplex canescens in Response to Salinity

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.00848

DOI=10.3389/fpls.2016.00848

ISSN=1664-462X

ABSTRACT=<p><italic>Atriplex canescens</italic> (fourwing saltbush) is a C<sub>4</sub> perennial fodder shrub with excellent resistance to salinity. However, the mechanisms underlying the salt tolerance in <italic>A. canescens</italic> are poorly understood. In this study, 5-weeks-old <italic>A. canescens</italic> seedlings were treated with various concentrations of external NaCl (0–400 mM). The results showed that the growth of <italic>A. canescens</italic> seedlings was significantly stimulated by moderate salinity (100 mM NaCl) and unaffected by high salinity (200 or 400 mM NaCl). Furthermore, <italic>A. canescens</italic> seedlings showed higher photosynthetic capacity under NaCl treatments (except for 100 mM NaCl treatment) with significant increases in net photosynthetic rate and water use efficiency. Under saline conditions, the <italic>A. canescens</italic> seedlings accumulated more Na<sup>+</sup> in either plant tissues or salt bladders, and also retained relatively constant K<sup>+</sup> in leaf tissues and bladders by enhancing the selective transport capacity for K<sup>+</sup> over Na<sup>+</sup> (ST value) from stem to leaf and from leaf to bladder. External NaCl treatments on <italic>A. canescens</italic> seedlings had no adverse impact on leaf relative water content, and this resulted from lower leaf osmotic potential under the salinity conditions. The contribution of Na<sup>+</sup> to the leaf osmotic potential (Ψ<italic>s</italic>) was sharply enhanced from 2% in control plants to 49% in plants subjected to 400 mM NaCl. However, the contribution of K<sup>+</sup> to Ψ<italic>s</italic> showed a significant decrease from 34% (control) to 9% under 400 mM NaCl. Interestingly, concentrations of betaine and free proline showed significant increase in the leaves of <italic>A. canescens</italic> seedlings, these compatible solutes presented up to 12% of contribution to Ψ<italic>s</italic> under high salinity. These findings suggest that, under saline environments, <italic>A. canescens</italic> is able to enhance photosynthetic capacity, increase Na<sup>+</sup> accumulation in tissues and salt bladders, maintain relative K<sup>+</sup> homeostasis in leaves, and use inorganic ions and compatible solutes for osmotic adjustment which may contribute to the improvement of water status in plant.</p>