Institute of Cellular and Molecular Botany, Department of Ecophysiology, University of Bonn, Kirschallee 1, 53115, Bonn, Germany.
Nees Institute for Biodiversity of Plants, University of Bonn, Meckenheimer Allee 170, 53115, Bonn, Germany.
Planta. 2021 Nov 26;255(1):1. doi: 10.1007/s00425-021-03785-z.
Time-dependent contact angle measurements of pure water on barley leaf surfaces allow quantifying the kinetics of surfactant diffusion into the leaf. Barley leaf surfaces were sprayed with three different aqueous concentrations (0.1, 1.0 and 10%) of a monodisperse (tetraethylene glycol monododecyl ether) and a polydisperse alcohol ethoxylate (BrijL4). After 10 min, the surfactant solutions on the leaf surfaces were dry leading to surfactant coverages of 1, 10 and 63 µg cm, respectively. The highest surfactant coverage (63 µg cm) affected leaf physiology (photosynthesis and water loss) rapidly and irreversibly and leaves were dying within 2-6 h. These effects on leaf physiology did not occur with the lower surfactant coverages (1 and 10 µg cm). Directly after spraying of 0.1 and 1.0% surfactant solution and complete drying (10 min), leaf surfaces were fully wettable for pure water and contact angles were 0°. Within 60 min (0.1% surfactant) and 6 h (1.0% surfactant), leaf surfaces were non-wettable again and contact angles of pure water were identical to control leaves. Scanning electron microscopy investigations directly performed after surfactant spraying and drying indicated that leaf surface wax crystallites were partially or fully covered by surfactants. Wax platelets with unaltered microstructure were fully visible again within 2 to 6 h after treatment with 0.1% surfactant solutions. Gas chromatographic analysis showed that surfactant amounts on leaf surfaces continuously disappeared over time. Our results indicate that surfactants, applied at realistic coverages between 1 and 10 µg cm to barley leaf surfaces, leading to total wetting (contact angles of 0°) of leaf surfaces, are rapidly taken up by the leaves. As a consequence, leaf surface non-wettability is fully reappearing. An irreversible damage of the leaf surface fine structure leading to enhanced wetting and increased foliar transpiration seems highly unlikely at low surfactant coverages of 1 µg cm.
时间依赖的纯水在大麦叶片表面的接触角测量可定量地描述表面活性剂向叶片内部的扩散动力学。大麦叶片表面喷涂了三种不同浓度（0.1%、1.0%和 10%）的单分散（四乙二醇单十二醚）和多分散醇乙氧基化物（BrijL4）水溶液。10 分钟后，叶片表面的表面活性剂溶液变干，导致表面活性剂覆盖率分别为 1、10 和 63μg/cm。最高的表面活性剂覆盖率（63μg/cm）快速且不可逆地影响叶片的生理学（光合作用和水分损失），叶片在 2-6 小时内死亡。这些对叶片生理学的影响不会出现在较低的表面活性剂覆盖率（1 和 10μg/cm）的情况下。在喷涂 0.1%和 1.0%表面活性剂溶液并完全干燥（10 分钟）后，直接测量叶片表面的纯水接触角为 0°，叶片表面完全润湿。在 60 分钟（0.1%表面活性剂）和 6 小时（1.0%表面活性剂）内，叶片表面再次变得不可润湿，纯水的接触角与对照叶片相同。在喷涂和干燥表面活性剂后直接进行的扫描电子显微镜研究表明，叶片表面蜡质晶体被部分或完全覆盖。用 0.1%表面活性剂处理 2 至 6 小时后，未改变微观结构的蜡质板又完全可见。气相色谱分析表明，随着时间的推移，叶片表面的表面活性剂数量不断减少。我们的研究结果表明，在大麦叶片表面应用 1 至 10μg/cm 之间的实际覆盖量的表面活性剂会导致叶片表面完全润湿（接触角为 0°），这些表面活性剂会被叶片迅速吸收。因此，叶片表面的非润湿性能会完全重新出现。在低表面活性剂覆盖率为 1μg/cm 时，表面活性剂对叶片表面的微观结构造成不可逆的损伤，从而导致表面润湿增加和叶片蒸腾增加的可能性很小。
