Photosynthetically-active radiation (PAR) affects transpirational water loss, yet we do not know through which mechanisms root water uptake is adjusted in parallel. Here, we exposed hydroponically-grown barley plants to three levels of PAR (Normal [control], Low, High) and focused on the role which aquaporins (AQPs), apoplastic barriers (Casparian bands, suberin lamellae) and root morphology play in the adjustment of root hydraulic conductivity (Lp). Plants were analysed when they were 14-18 day (d) old. Root and cell Lp, which involves AQP activity, was determined through exudation and cell pressure probe measurements, respectively. Gene expression of AQPs was analysed through qPCR. The formation of apoplastic barriers was studied through staining of cross-sections. The rate of transpirational water loss per plant and unit leaf area increased in response to High-PAR and decreased in response to Low-PAR treatments, both during day and night. Hydraulic conductivity in roots decreased significantly at organ and cell level in response to Low-PAR, and increased (organ) or did not change (cell level) in response to High-PAR. The formation of apoplastic barriers was little affected by PAR. Gene expression of AQPs tended to be highest in the Low-PAR treatment. Lateral roots, showing few apoplastic barriers, contributed the least in Low- and the most to root surface area in High-PAR plants. It is concluded that barley plants which experience changes in shoot transpirational water loss in response to PAR adjust root water uptake through changes in root Lp, and that these changes are mediated through altered AQP activity and root morphology. This article is protected by copyright. All rights reserved.

中文翻译：

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光合有效辐射对大麦 (Hordeum vulgare L.) 的根和细胞水力学影响显着

光合有效辐射 (PAR) 会影响蒸腾水分流失，但我们不知道通过哪些机制并行调节根部吸水量。在这里，我们将水培种植的大麦植物暴露于三个水平的 PAR（正常 [对照]、低、高），并重点研究了水通道蛋白 (AQP)、质外体屏障（Casparian 带、木栓质薄片）和根形态在根部水力传导率 (Lp) 的调整。植物在 14-18 天 (d) 龄时进行分析。根和细胞 Lp 涉及 AQP 活性，分别通过渗出和细胞压力探针测量确定。通过qPCR分析AQPs的基因表达。通过横截面的染色研究质外体屏障的形成。在白天和晚上，每株植物和单位叶面积的蒸腾水分损失率响应高 PAR 增加，响应低 PAR 处理减少。根的导水率在器官和细胞水平上显着降低以响应低 PAR，而在响应高 PAR 时增加（器官）或不改变（细胞水平）。PAR 对质外体屏障的形成影响很小。AQPs 的基因表达往往在低 PAR 处理中最高。侧根显示出很少的质外体屏障，对高 PAR 植物的根表面积贡献最小，而对根表面积的贡献最大。得出的结论是，响应 PAR 经历地上部蒸腾失水变化的大麦植物通过根 Lp 的变化来调节根吸水量，并且这些变化是通过改变 AQP 活性和根形态介导的。本文受版权保护。版权所有。