Institute of Systematic Botany and Ecology, Ulm University, Ulm, Germany.
Laboratory of Plant Physiology "Coaracy M. Franco", Center R&D in Ecophysiology and Biophysics, Agronomic Institute (IAC), Campinas, Brazil.
Plant Cell Environ. 2021 May;44(5):1329-1345. doi: 10.1111/pce.14016. Epub 2021 Feb 18.
Embolism spreading in dehydrating angiosperm xylem is driven by gas movement between embolized and sap-filled conduits. Here we examine how the proximity to pre-existing embolism and hydraulic segmentation affect embolism propagation. Based on the optical method, we compare xylem embolism resistance between detached leaves and leaves attached to branches, and between intact leaves and leaves with cut minor veins, for six species. Embolism resistance of detached leaves was significantly lower than that of leaves attached to stems, except for two species, with all vessels ending in their petioles. Cutting of minor veins showed limited embolism spreading in minor veins near the cuts prior to major veins. Moreover, despite strong agreement in the overall embolism resistance of detached leaves between the optical and pneumatic method, minor differences were observed during early stages of embolism formation. We conclude that embolism resistance may represent a relative trait due to an open-xylem artefact, with embolism spreading possibly affected by the proximity and connectivity to pre-existing embolism as a gas source, while hydraulic segmentation prevents such artefact. Since embolism formation may not rely on a certain pressure difference threshold between functional and embolized conduits, we speculate that embolism is facilitated by pressure-driven gas diffusion across pit membranes.
在脱水的被子植物木质部中，栓塞的扩散是由栓塞和充满汁液的导管之间的气体运动驱动的。在这里，我们研究了预先存在的栓塞和水力分段如何影响栓塞的传播。基于光学方法，我们比较了六个物种的离体叶片和附生叶片、完整叶片和切去小脉叶片之间的木质部栓塞阻力。除了两个种以外，所有终生于叶柄的种的离体叶片栓塞阻力显著低于附生茎上的叶片。小脉的切割显示，在大脉之前，切割处附近的小脉中的栓塞传播有限。此外，尽管光学和气动方法在离体叶片的整体栓塞阻力上具有很强的一致性，但在栓塞形成的早期阶段观察到了一些细微的差异。我们得出结论，栓塞阻力可能代表一种相对的特征，因为存在开放式木质部的假象，栓塞的传播可能受到预先存在的栓塞作为气体源的接近程度和连通性的影响，而水力分段则阻止了这种假象。由于栓塞的形成可能不依赖于功能导管和栓塞导管之间的特定压力差阈值，我们推测栓塞是通过压力驱动的气体在纹孔膜上扩散来促进的。
