Plant salt tolerance is closely associated with a high rate of root growth. Although root growth is governed by cell-wall and apoplastic pH, the relationship between these factors in the root elongation zone under salinity stress remains unclear. Here, we assess apoplastic pH, pH- and expansin-dependent cell-wall extensibility, and expansin expression in the root elongation zone of salt-sensitive (Yongliang-15) and -tolerant (JS-7) cultivars under salinity stress. A six-day 80 mM NaCl treatment significantly reduced apical-root apoplastic pH, from 6.2 to 5.3, in both cultivars. Using a pH-dependent cell-wall extensibility experiment, we found that, under 0 mM NaCl treatment, the optimal pH for cell-wall loosening was 6.0 in the salinity-tolerant cultivar and 4.6 in the salinity-sensitive cultivar. Under 80 mM treatment, a pH of 5.0 mitigated the cell-wall stiffness caused by salinity stress in the salinity-tolerant cultivar, but promoted cell-wall stiffening in the salinity-sensitive cultivar. These changes in pH-dependent cell-wall extensibility are consistent with differences in the root growth of two cultivars under salinity stress. Exogenous expansin application, and expansin expression experiments, we found that salinity stress altered expansin expression, differentially affecting cell-wall extensibility under pH 5.0 and 6.0. TaEXPA7 and TaEXPA8 induced cell-wall loosening at pH 5.0, whereas TaEXPA5 induced cell-wall loosening at pH 6.0. These results elucidate the relationship between expansin and cell-wall extensibility in the root elongation zone, with important implications for enhancing plant growth under salinity stress.

中文翻译：

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根尖质外体酸化影响盐分胁迫下小麦细胞壁的延伸性

植物的耐盐性与高根生长密切相关。尽管根的生长受细胞壁和质外性pH的控制，但盐分胁迫下根伸长区中这些因素之间的关系仍不清楚。在这里，我们评估盐分胁迫下盐敏感（Yongliang-15）和耐盐品种（JS-7）的根伸长区的质外性pH，pH和expanins依赖性的细胞壁可扩展性以及expansin的表达。在两个品种中，为期六天的80 mM NaCl处理将根尖质外生pH值从6.2显着降低至5.3。使用pH依赖性细胞壁可扩展性实验，我们发现，在0 mM NaCl处理下，耐盐性品种的细胞壁松弛的最佳pH为6.0，而对盐度敏感的品种的最佳pH为4.6。在80 mM处理下，pH为5。0减轻了耐盐品种的盐胁迫引起的细胞壁僵硬，但促进了对盐敏感性敏感品种的细胞壁僵硬。pH依赖性细胞壁可扩展性的这些变化与盐胁迫下两个品种根系生长的差异一致。外源性expansin应用和expansin表达实验，我们发现盐度应力改变了expansin表达，在pH 5.0和6.0下差异影响细胞壁的延伸性。TaEXPA7和TaEXPA8在pH 5.0时诱导细胞壁松弛，而TaEXPA5在pH 6.0时诱导细胞壁松弛。这些结果阐明了伸展蛋白与根伸长区中细胞壁可扩展性之间的关系，对盐分胁迫下植物的生长具有重要意义。