Ingram Stephen, Jansen Steven, Schenk H Jochen
Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, 00560 Helsinki, Finland.
Institute of Botany, Ulm University, 89081 Ulm, Germany.
Nanomaterials (Basel). 2023 May 31;13(11):1776. doi: 10.3390/nano13111776.
One of the more surprising occurrences of bulk nanobubbles is in the sap inside the vascular transport system of flowering plants, the xylem. In plants, nanobubbles are subjected to negative pressure in the water and to large pressure fluctuations, sometimes encompassing pressure changes of several MPa over the course of a single day, as well as wide temperature fluctuations. Here, we review the evidence for nanobubbles in plants and for polar lipids that coat them, allowing nanobubbles to persist in this dynamic environment. The review addresses how the dynamic surface tension of polar lipid monolayers allows nanobubbles to avoid dissolution or unstable expansion under negative liquid pressure. In addition, we discuss theoretical considerations about the formation of lipid-coated nanobubbles in plants from gas-filled spaces in the xylem and the role of mesoporous fibrous pit membranes between xylem conduits in creating the bubbles, driven by the pressure gradient between the gas and liquid phase. We discuss the role of surface charges in preventing nanobubble coalescence, and conclude by addressing a number of open questions about nanobubbles in plants.
大体积纳米气泡较为令人惊讶的一个出现位置是在开花植物维管运输系统（木质部）内的汁液中。在植物中，纳米气泡会受到水中的负压以及较大的压力波动影响，有时在一天之内压力变化可达几兆帕，同时还会面临较大的温度波动。在此，我们综述了植物中纳米气泡以及包裹它们的极性脂质的相关证据，这些极性脂质能使纳米气泡在这种动态环境中持续存在。本综述探讨了极性脂质单分子层的动态表面张力如何使纳米气泡在负液体压力下避免溶解或不稳定膨胀。此外，我们还讨论了关于植物中脂质包裹纳米气泡从木质部充气空间形成的理论思考，以及木质部导管之间的中孔纤维状纹孔膜在由气液相压力梯度驱动产生气泡过程中的作用。我们讨论了表面电荷在防止纳米气泡聚并中的作用，并通过阐述关于植物中纳米气泡的一些未解决问题来结束本文。
