Plant responses to soil drying and the metabolic basis of drought-induced limitations in stomatal opening are still being discussed. In this study, we investigate the roles of root-born chemical and hydraulic signals on stomatal regulation in wheat genotypes as affected by soil drought and vapour pressure deficit. Twelve consecutive pot experiments were carried out in a glasshouse. Two bread wheat cultivars (Gönen and Basribey) were subjected to drought under high and low vapour pressure deficit (VPD) in a growth chamber. Total dry matter, specific leaf area, xylem ABA content, xylem osmotic potential, xylem pH, root water potential (RWP), stomatal conductance, leaf ABA content and photosynthetic activity were determined daily during 6 days after the onset of treatments (DAT). In the first phase of drought stress, soil drying induced an increase in the xylem ABA with a peak 3 DAT while RWP drastically decreased during the same period. Then the osmotic potential of leaves decreased and leaf ABA content increased 4 DAT. A similar peak was observed for stomatal conductance during the early stress phase, and it became stable and significantly higher than in well-watered conditions especially in high vapour deficit conditions (H-VPD). Furthermore, xylem pH and xylem osmotic potential appeared to be mostly associated with atmospheric moisture content than soil water availability. The results are discussed regarding possible drought adaptation of wheat under different atmospheric humidity.

中文翻译：

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大气和土壤缺水引起小麦（Triticum aestivum L.）化学和水力信号的变化

植物对土壤干燥的反应和干旱引起的气孔开放限制的代谢基础仍在讨论中。在这项研究中，我们研究了根生化学和水力信号对受土壤干旱和水汽压不足影响的小麦基因型气孔调节的作用。在温室中连续进行了 12 次盆栽试验。在生长室中，两个面包小麦品种（Gönen 和 Basribey）在高和低蒸气压不足 (VPD) 条件下遭受干旱。在处理开始后的 6 天内每天测定总干物质、比叶面积、木质部 ABA 含量、木质部渗透势、木质部 pH 值、根水势 (RWP)、气孔导度、叶片 ABA 含量和光合活性 (DAT)。在干旱胁迫的第一阶段，土壤干燥导致木质部 ABA 增加，峰值为 3 DAT，而 RWP 在同一时期急剧下降。然后叶片渗透压降低，叶片ABA含量增加4 DAT。在早期胁迫阶段观察到类似的气孔导度峰值，并且它变得稳定并且显着高于水分充足条件下，特别是在高水汽亏缺条件下（H-VPD）。此外，木质部 pH 值和木质部渗透势似乎主要与大气水分含量相关，而不是与土壤水分有效性相关。讨论了不同大气湿度下小麦可能的干旱适应性结果。在早期胁迫阶段观察到类似的气孔导度峰值，并且它变得稳定并且显着高于水分充足条件下，特别是在高水汽亏缺条件下（H-VPD）。此外，木质部 pH 值和木质部渗透势似乎主要与大气水分含量相关，而不是与土壤水分有效性相关。讨论了不同大气湿度下小麦可能的干旱适应性结果。在早期胁迫阶段观察到类似的气孔导度峰值，并且它变得稳定并且显着高于水分充足条件下，特别是在高水汽亏缺条件下（H-VPD）。此外，木质部 pH 值和木质部渗透势似乎主要与大气水分含量相关，而不是与土壤水分有效性相关。讨论了不同大气湿度下小麦可能的干旱适应性结果。