Ma Q, Li XY, Yuan HJ, Hu J, Wei L, Bao AK, Zhang JL, Wang SM*. ZxSOS1 is essential for long-distance transport and spatial distribution of Na⁺ and K⁺ in the xerophyte Zygophyllum xanthoxylum. Plant and Soil. 2014 374(1-2): 661-676

摘要：

Background and aims: Two major adaptive strategies used by Zygophyllum xanthoxylum, a C₃ succulent xerophyte, against arid environments are absorbing a great quantity of Na⁺ from low-salinity soil which is efficiently transported to the leaves, and maintaining the stability of K⁺ concentration in those leaves. The plasma membrane Na⁺/H⁺ antiporter SOS1 has been suggested to be involved in Na⁺ transport and correlated with K⁺ nutrition in glycophytes. In this study, we investigated the function of the plasma membrane Na⁺/H⁺ antiporter ZxSOS1 in long-distance transport and spatial distribution of Na⁺ and K⁺ in the xerophyte Z. xanthoxylum. Methods: The responses of ZxSOS1 to NaCl, KCl treatments and osmotic stress were investigated by semi-quantitative RT-PCR, then the role of ZxSOS1 in regulating plant growth and Na⁺, K⁺ transport and spatial distribution in Z. xanthoxylum was studied by using post-transcriptional gene silencing. Results: We found that ZxSOS1 was preferentially expressed in roots and was induced and regulated by salt treatments and osmotic stress. Using post-transcriptional gene silencing, we found that ZxSOS1-silenced plants exhibited reduced growth rate compared to wild-type (WT) plants under both normal and saline conditions. ZxSOS1-silenced plants accumulated more Na⁺ in their roots but less Na⁺ in leaves and stems than WT under 50 mM NaCl. Furthermore, ZxSOS1-silenced plants had a lower net K⁺ uptake rate than WT plants under both normal and saline conditions, and more interestingly, accumulated less K⁺ in leaves under normal conditions than WT plants. ZxSOS1-silenced plants also showed a decreased concentration and spatial distribution of K⁺ in leaves and roots than WT under 50 mM NaCl. In addition, ZxSOS1-silenced plants possessed an increased selective transport (ST) capacity for K⁺ over Na⁺ from root to stem while a decreased ST value from stem to leaf compared with WT plants when both were grown in 50 mM NaCl. Conclusions: These results demonstrate that ZxSOS1 is not only essential in long-distance transport and spatial distribution of Na⁺ and even K⁺, but also vital for regulating K⁺ and Na⁺ transport system and maintaining Na⁺ and K⁺ homeostasis in Z. xanthoxylum, thereby regulating its normal growth.