Levionnois Sébastien, Kaack Lucian, Heuret Patrick, Abel Nina, Ziegler Camille, Coste Sabrina, Stahl Clément, Jansen Steven
UMR EcoFoG, AgroParisTech, CIRAD, CNRS, INRAE, Université des Antilles, Université de Guyane, Kourou 97310, France.
UMR AMAP, Univ. Montpellier, CIRAD, CNRS, INRAE, IRD, Montpellier 34000, France.
Plant Physiol. 2022 Aug 29;190(1):371-386. doi: 10.1093/plphys/kiac223.
Embolism spreading in xylem is an important component of plant drought resistance. Since embolism resistance has been shown to be mechanistically linked to pit membrane characters in stem xylem, we speculate that similar mechanisms account for leaf xylem. We conducted transmission electron microscopy to investigate pit membrane characters in leaf xylem across 18 Neotropical tree species. We also conducted gold perfusion and polar lipid detection experiments on three species covering the full range of leaf embolism resistance. We then related these observations to previously published data on embolism resistance of leaf xylem. We also incorporated previously published data on stem embolism resistance and stem xylem pit membranes to investigate the link between vulnerability segmentation (i.e. difference in embolism resistance) and leaf-stem anatomical variation. Maximum pit membrane thickness (Tpm,max) and the pit membrane thickness-to-diameter ratio (Tpm,max/Dpm) were predictive of leaf embolism resistance, especially when vestured pits were taken into account. Variation in Tpm,max/Dpm was the only trait predictive of vulnerability segmentation between leaves and stems. Gold particles of 5- and 10-nm infiltrated pit membranes in three species, while the entry of 50-nm particles was blocked. Moreover, polar lipids were associated with inner conduit walls and pits. Our results suggest that mechanisms related to embolism spreading are determined by Tpm, pore constrictions (i.e. the narrowest bottlenecks along pore pathways), and lipid surfactants, which are largely similar between leaf and stem xylem and between temperate and tropical trees. However, our mechanistic understanding of embolism propagation and the functional relevance of Tpm,max/Dpm remains elusive.
木质部中栓塞的扩展是植物抗旱性的一个重要组成部分。由于已表明栓塞抗性在机制上与茎木质部的纹孔膜特征相关，我们推测类似的机制也适用于叶木质部。我们进行了透射电子显微镜观察，以研究18种新热带树种叶木质部的纹孔膜特征。我们还对三种具有不同叶栓塞抗性的树种进行了金灌注和极性脂质检测实验。然后，我们将这些观察结果与先前发表的关于叶木质部栓塞抗性的数据相关联。我们还纳入了先前发表的关于茎栓塞抗性和茎木质部纹孔膜的数据，以研究脆弱性分割（即栓塞抗性差异）与叶 - 茎解剖结构变化之间的联系。最大纹孔膜厚度（Tpm,max）和纹孔膜厚度与直径之比（Tpm,max/Dpm）可预测叶栓塞抗性，尤其是在考虑具缘纹孔时。Tpm,max/Dpm的变化是预测叶与茎之间脆弱性分割的唯一特征。在三种树种中，5纳米和10纳米的金颗粒渗入了纹孔膜，而50纳米颗粒的进入则被阻断。此外，极性脂质与导管内壁和纹孔相关。我们的结果表明，与栓塞扩展相关的机制由Tpm、孔隙收缩（即沿孔隙通道最窄的瓶颈处）和脂质表面活性剂决定，这些在叶和茎木质部之间以及温带和热带树木之间基本相似。然而，我们对栓塞传播的机制理解以及Tpm,max/Dpm的功能相关性仍然不清楚。
