In apple (Malus) cultivation, the adaptability of rootstocks has a fundamental influence on multiple abiotic-stress resistance properties of their scions. Here, we investigated the high-salt resistance of apple rootstocks, by treating 2-year-old apple trees consisting of the ‘Fuji’ cultivar grafted onto three different dwarfing rootstocks (SH6, M9-T337 and G935) with a high-salt solution for 30 days. We found that the high-salt stress caused leaf yellowing and growth inhibition to all apple plants, and that the most serious reduction in relative chlorophyll content, plant height and biomass accumulation was associated with the SH6 rootstock. In addition, based on the salt injury index, the high-salt resistance of the ‘Fuji’ scion on the three dwarfing rootstocks was ranked as G935 > M9-T337 > SH6. In addition, analysis of mineral elemental composition showed that the Na+ content in ‘Fuji’ leaves on the G935 rootstock increased less than twofold compared to the control, whereas those on the SH6 rootstock increased nearly 20-fold, accompanied with reduced K and Fe element absorption under high-salt treatments. Expression analysis of nine Na+ transport-related genes indicated that in the salt overly sensitive (SOS) pathway, the SOS1, SOS2 and SOS3 genes showed considerably greater induction by high-salt stress in G935 roots than in SH6 roots. Given the Na+ content detected in roots of different rootstocks, we propose that more efficient Na+ extracellular efflux in G935 roots, rather than intracellular Na+ compartmentalization, contributed to the improved characteristics of the G935 rootstock under high-salt conditions.

中文翻译：

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苹果矮化砧木的 Na+ 流出与其接穗的高盐抗性有关

在苹果（Malus）栽培中，砧木的适应性对其接穗的多种非生物胁迫抗性具有根本性的影响。在这里，我们通过用高盐溶液处理由嫁接到三种不同矮化砧木（SH6、M9-T337 和 G935）上的“富士”品种组成的 2 年生苹果树，研究了苹果砧木的高盐抗性30 天。我们发现高盐胁迫导致所有苹果植株叶片变黄和生长受到抑制，相对叶绿素含量、株高和生物量积累最严重的降低与 SH6 砧木有关。此外，根据盐害指数，'富士'接穗对三个矮化砧木的高抗盐性排序为G935>M9-T337>SH6。此外，矿物元素组成分析表明，与对照相比，G935 砧木上'富士'叶片的 Na+ 含量增加了不到 2 倍，而 SH6 砧木上的 Na+ 含量增加了近 20 倍，伴随着高浓度下 K 和 Fe 元素吸收降低- 盐处理。九个 Na+ 转运相关基因的表达分析表明，在盐过度敏感（SOS）途径中，SOS1、SOS2 和 SOS3 基因在 G935 根中显示出比在 SH6 根中更高的高盐胁迫诱导。鉴于在不同砧木根中检测到的 Na+ 含量，我们提出 G935 根中更有效的 Na+ 细胞外流出，而不是细胞内 Na+ 区室化，有助于改善 G935 砧木在高盐条件下的特性。